基本情報

所属

• 北極域研究センター

職名

• 教授

ホームページURL

http://wwwoa.ees.hokudai.ac.jp/people/yasuf/

科研費研究者番号

• 20250508

J-Global ID

• 200901037096187792

研究キーワード

• ポリニヤ   海洋大循環   南極底層水   海氷   オホーツク海   南大洋   

研究分野

• 自然科学一般 / 大気水圏科学 / 極域海洋学

担当教育組織

•  修士課程　環境科学院
•  博士課程　環境科学院

職歴

• 2018年10月 - 現在 北海道大学北極域研究センター 大気圏・水圏研究グループ 教授
• 2011年02月 - 2018年09月 北海道大学 低温科学研究所 水・物質循環部門 准教授
• 2008年10月 - 2011年01月 北海道大学 低温科学研究所 水・物質循環部門 助教
• 2007年04月 - 2008年09月 北海道大学 低温科学研究所 寒冷海洋圏科学部門 助教
• 1995年04月 - 2007年03月 北海道大学 低温科学研究所 寒冷海洋圏科学部門 助手
• 1992年11月 - 1995年03月 北海道大学 低温科学研究所 海洋学部門 助手

学歴

• 1986年10月 - 1992年10月   ノバ大学   海洋研究所
•         - 1992年   Nova University Graduate School
•         - 1986年03月   北海道大学   理学部   地球物理学科
•         - 1986年   北海道大学

所属学協会

• 日本海洋学会   The Oceanography Society   American Geophysical Union   The Oceanography Society   American Geophysical Union   The Oceanographic Society of Japan   

研究活動情報

論文

• Particle-tracking experiments of coastal-origin sea ice that could induce high biological productivity in the Sea of Okhotsk

  Mizuki Kuga, Kay I. Ohshima, Noriaki Kimura, Kazuki Nakata, Yasushi Fukamachi

  Journal of Oceanography 79 2 145 - 159 2022年11月28日 [査読有り]
  
• Dominant frazil ice production in the Cape Darnley polynya leading to Antarctic Bottom Water formation

  Kay I. Ohshima, Yasushi Fukamachi, Masato Ito, Kazuki Nakata, Daisuke Simizu, Kazuya Ono, Daiki Nomura, Gen Hashida, Takeshi Tamura

  Science Advances 8 42 2022年10月21日 [査読有り]
   

  Antarctic Bottom Water (AABW) occupies the abyssal layer of the world ocean and contributes to the global overturning circulation. It originates from dense shelf water, which forms from brine rejection during sea ice production. An important region of AABW formation has been identified off the Cape Darnley polynya. However, it remains unclear why and how high ice production leads to AABW formation. Using moored acoustic measurements and a satellite microwave algorithm, we reveal that underwater frazil ice dominates in the polynya. This underwater ice formation prevents heat-insulating surface-cover ice forming, thereby enabling efficient ice production. The high ice production in the nearshore and longer residence times create high-salinity source water for the AABW. Underwater frazil ice occurs as long as strong winds continue and occasionally penetrates depths of at least 80 m. Deep-penetrating frazil ice is particularly prominent in this polynya, while it also occurs in other Antarctic coastal polynyas.
• Effects of the glacial meltwater supply on carbonate chemistry in Bowdoin Fjord, Northwestern Greenland

  Takahito Horikawa, Daiki Nomura, Naoya Kanna, Yasushi Fukamachi, Shin Sugiyama

  Frontiers in Marine Science 9 2022年07月22日 

  To understand the effects of the glacial meltwater supply on carbonate chemistry and the air–sea CO₂ flux within the fjord, water samples were collected in Bowdoin Fjord in northwestern Greenland for dissolved inorganic carbon (DIC) concentration, total alkalinity (TA), oxygen isotopic ratio (δ¹⁸O), and chlorophyll a concentration analyses in the summers of 2016 and 2017. The partial pressure of CO₂ (pCO₂) in surface water, calculated from DIC and TA, was less than 200 µatm, and was significantly lower than that in the atmosphere (399 ± 3 µatm). Therefore, surface water of the fjord acts as sink for CO₂ in the atmosphere (–4.9 ± 0.7 mmol m^–2 d^–1). To evaluate the effects of freshwater and land-derived substances by glacial meltwater on pCO₂ in the fjord, we calculated the changes of pCO₂ in salinity and carbonate chemistry that would result from the inflow of glacial meltwater into the fjord. The calculated pCO₂ was high near the calving front, where the contribution of glacier meltwater was significant. Examination of the relationship between salinity-normalized DIC and TA, which was considered DIC and TA input from the land, suggested that the land-derived high pCO₂ freshwater affected mainly by the remineralization of the organic matter by bacterial activity was supplied to the Bowdoin Fjord.
• A neural network-based method for satellite-based mapping of sediment-laden sea ice in the Arctic

  Hisatomo Waga, Hajo Eicken, Bonnie Light, Yasushi Fukamachi

  Remote Sensing of Environment 270 112861 - 112861 2022年03月 [査読有り]
   

  Sediment-laden sea ice is a ubiquitous phenomenon in the Arctic Ocean and its marginal seas. This study presents a satellite-based approach at quantifying the distribution of sediment-laden ice that allows for more extensive observations in both time and space to monitor spatiotemporal variations in sediment-laden ice. A structural-optical model coupled with a four-stream multilayer discrete ordinates method radiative transfer model was used to examine surface spectral albedo for four surface types: clean ice, sediment-laden ice with 15 different sediment loadings from 25 to 1000 g m(-3), ponded ice, and ice-free open water. Based on the fact that the spectral characteristics of sediment-laden ice differ from those other surface types, fractions of sediment-laden ice were estimated from the remotely-sensed surface reflectance by a spectral unmixing algorithm using a least square method. Sensitivity analyses demonstrated that a combination of sediment loads of 50 and 500 g m(-3) effectively represents the areal fraction of sediment-laden ice with a wide range of sediment loads. The estimated fractions of each surface type and corresponding remotely-sensed surface reflectances were used to train an artificial neural network to speed up processing relative to the least squares method. Comparing the fractions of sediment-laden ice derived from these two approaches yielded good agreements for areal fractions of sediment-laden ice, highlighting the superior performance of the neural network for processing large datasets. Although our approach contains potential uncertainties associated with methodological limitations, spatiotemporal variations in sediment-laden ice exhibited reasonable agreement with spatial patterns and seasonal variations reported in the literature on in situ observations of sediment-laden ice. Systematic satellite-based monitoring of sediment-laden ice distribution can provide extensive, sustained, and cost-effective observations to foster our under-standing of the role of sediment-laden ice in a wide variety of research fields including sediment transport and biogeochemical cycling.
• Oceanic conditions in the Barrow Coastal Polynya revealed by a 10-year mooring time series

  Daisuke Hirano, Yasushi Fukamachi, Kay I. Ohshima, Masato Ito, Takeshi Tamura, Daisuke Simizu, Toru Takatsuka, Andrew R. Mahoney, Joshua Jones, Craig George, Billy Adams, Hajo Eicken

  Progress in Oceanography 102781 - 102781 2022年03月
• Variability in spring phytoplankton blooms associated with ice retreat timing in the Pacific Arctic from 2003–2019

  Hisatomo Waga, Hajo Eicken, Toru Hirawake, Yasushi Fukamachi

  PLOS ONE 16 12 e0261418 - e0261418 2021年12月16日 

  The Arctic is experiencing rapid changes in sea-ice seasonality and extent, with significant consequences for primary production. With the importance of accurate monitoring of spring phytoplankton dynamics in a changing Arctic, this study further examines the previously established critical relationship between spring phytoplankton bloom types and timing of the sea-ice retreat for broader temporal and spatial coverages, with a particular focus on the Pacific Arctic for 2003–2019. To this end, time-series of satellite-retrieved phytoplankton biomass were modeled using a parametric Gaussian function, as an effective approach to capture the development and decay of phytoplankton blooms. Our sensitivity analysis demonstrated accurate estimates of timing and presence/absence of peaks in phytoplankton biomass even with some missing values, suggesting the parametric Gaussian function is a powerful tool for capturing the development and decay of phytoplankton blooms. Based on the timing and presence/absence of a peak in phytoplankton biomass and following the classification developed by the previous exploratory work, spring bloom types are classified into three groups (under-ice blooms, probable under-ice blooms, and marginal ice zone blooms). Our results showed that the proportion of under-ice blooms was higher in the Chukchi Sea than in the Bering Sea. The probable under-ice blooms registered as the dominant bloom types in a wide area of the Pacific Arctic, whereas the marginal ice zone bloom was a relatively minor bloom type across the Pacific Arctic. Associated with a shift of sea-ice retreat timing toward earlier dates, we confirmed previous findings from the Chukchi Sea of recent shifts in phytoplankton bloom types from under-ice blooms to marginal ice zone blooms and demonstrated that this pattern holds for the broader Pacific Arctic sector for the time period 2003–2019. Overall, the present study provided additional evidence of the changing sea-ice retreat timing that can drive variations in phytoplankton bloom dynamics, which contributes to addressing the detection and consistent monitoring of the biophysical responses to the changing environments in the Pacific Arctic.
• Subglacial discharge controls seasonal variations in the thermal structure of a glacial lake in Patagonia

  Shin Sugiyama, Masahiro Minowa, Yasushi Fukamachi, Shuntaro Hata, Yoshihiro Yamamoto, Tobias Sauter, Christoph Schneider, Marius Schaefer

  Nature Communications 12 1 2021年12月 

  Water temperature in glacial lakes affects underwater melting and calving of glaciers terminating in lakes. Despite its importance, seasonal lake temperature variations are poorly understood because taking long-term measurements near the front of calving glaciers is challenging. To investigate the thermal structure and its seasonal variations, we performed year-around temperature and current measurement at depths of 58–392 m in Lago Grey, a 410-m-deep glacial lake in Patagonia. The measurement revealed critical impacts of subglacial discharge on the lake thermal condition. Water below a depth of ~100 m showed the coldest temperature in mid-summer, under the influence of glacial discharge, whereas temperature in the upper layer followed a seasonal variation of air temperature. The boundary of the lower and upper layers was controlled by the depth of a sill which blocks outflow of dense and cold glacial meltwater. Our data implies that subglacial discharge and bathymetry dictate mass loss and the retreat of lake-terminating glaciers. The cold lakewater hinders underwater melting and facilitates formation of a floating terminus.
• Underwater frazil ice and its suspension depth detected from ADCP backscatter data around sea ice edge in the Sea of Okhotsk

  Masato Ito, Kay I. Ohshima, Yasushi Fukamachi, Genta Mizuta, Yoshimu Kusumoto, Takashi Kikuchi

  Cold Regions Science and Technology 103382 - 103382 2021年08月
• Seasonal Evolution of Cape Darnley Bottom Water Revealed by Mooring Measurements

  Genta Mizuta, Yasushi Fukamachi, Daisuke Simizu, Yoshimasa Matsumura, Yujiro Kitade, Daisuke Hirano, Masakazu Fujii, Yoshifumi Nogi, Kay Ohshima

  FRONTIERS IN MARINE SCIENCE 8 2021年08月 

  This study examines the seasonal evolution of Cape Darnley Bottom Water (CDBW), using the results of mooring and hydrographic measurements in the slope region off Cape Darnley in 2008-2009 and 2013-2014. Newly formed CDBW began reaching the western and nearshore part of the slope region off Cape Darnley in April, spread to the offshore and eastern part in May, and reached the easternmost part in September. The potential temperature and salinity decreased and the neutral density increased when newly formed CDBW reached mooring sites. Potential temperature-salinity properties of CDBW changed over time and location. The salinity of the source water of CDBW estimated from potential temperature-salinity diagrams started to increase at a nearshore mooring in late April, which is about 2 months after the onset of sea-ice production, and continued to increase during the ice production season. It is most probable that the accumulation of brine in the Cape Darnley polynya produces the seasonal variation of potential temperature-salinity properties of CDBW. Two types of CDBW were identified. Cold and less saline CDBW and warm and saline CDBW were present in Wild and Daly Canyons, respectively. This indicates that the salinity of the source water of CDBW increased in the westward direction. CDBW exhibited short-term variability induced by baroclinic instability.
• Status and trends of Arctic Ocean environmental change and its impacts on marine biogeochemistry: Findings from the ArCS project

  Takashi Kikuchi, Shigeto Nishino, Amane Fujiwara, Jonaotaro Onodera, Michiyo Yamamoto-Kawai, Kohei Mizobata, Yasushi Fukamachi, Eiji Watanabe

  POLAR SCIENCE 27 2021年03月 

  Ocean observation research theme under ArCS project, ?Theme 4: Observational research on Arctic Ocean environmental changes?, aimed to elucidate the status and trends of ongoing Arctic Ocean environmental changes and to evaluate their impacts on Arctic marine ecosystem and the global climate system. For these purposes, we conducted field observations, mooring observations, laboratory experiments, numerical modeling, and international collaborative research focusing on the Pacific Arctic Region (PAR) and from Pan-Arctic point of views. As a result, we have published several scientific studies on environmental changes and their impact on the climate and ecosystem. In this manuscript, we compiled these results with some concluding remarks. We found physical environmental changes of water cycle, sea-ice and ocean conditions, heat transport, and ocean mixing in the Arctic Ocean and surrounding areas. We also examined chemical properties, carbon, cycle, and ocean acidification in the Arctic Ocean. In addition, new findings regarding impacts of sea-ice reduction to primary productivities were published. For public outreach of Arctic research, we were able to develop an educational tool (a board game named ?The Arctic?) in collaboration with Themes 6 and 7.
• Rapidly changing glaciers, ocean and coastal environments, and their impact on human society in the Qaanaaq region, northwestern Greenland

  Shin Sugiyama, Naoya Kanna, Daiki Sakakibara, Takuto Ando, Izumi Asaji, Ken Kondo, Yefan Wang, Yoshiki Fujishi, Shungo Fukumoto, Evgeniy Podolskiy, Yasushi Fukamachi, Minori Takahashi, Sumito Matoba, Yoshinori Iizuka, Ralf Greve, Masato Furuya, Kazutaka Tateyama, Tatsuya Watanabe, Shintaro Yamasaki, Atsushi Yamaguchi, Bungo Nishizawa, Kohei Matsuno, Daiki Nomura, Yuta Sakuragi, Yoshimasa Matsumura, Yoshihiko Ohashi, Teruo Aoki, Masashi Niwano, Naotaka Hayashi, Masahiro Minowa, Guillaume Jouvet, Eef van Dongen, Andreas Bauder, Martin Funk, Anders Anker Bjork, Toku Oshima

  POLAR SCIENCE 27 2021年03月 

  Environments along the coast of Greenland are rapidly changing under the influence of a warming climate in the Arctic. To better understand the changes in the coastal environments, we performed researches in the Qaanaaq region in northwestern Greenland as a part of the ArCS (Arctic Challenge for Sustainability) Project. Mass loss of ice caps and marine-terminating outlet glaciers were quantified by field and satellite observations. Measurements and sampling in fjords revealed the important role of glacial meltwater discharge in marine ecosystems. Flooding of a glacial stream in Qaanaaq and landslides in a nearby settlement were investigated to identify the drivers of the incidents. Our study observed rapid changes in the coastal environments, and their critical impact on the society in Qaanaaq. We organized workshops with the residents to absorb local and indigenous knowledge, as well as to share the results and data obtained in the project. Continuous effort towards obtaining long-term observations requiring involvement of local communities is crucial to contribute to a sustainable future in Greenland.
• Iron Supply by Subglacial Discharge Into a Fjord Near the Front of a Marine‐Terminating Glacier in Northwestern Greenland

  Naoya Kanna, Shin Sugiyama, Yasushi Fukamachi, Daiki Nomura, Jun Nishioka

  Global Biogeochemical Cycles 34 10 2020年10月
• Sea ice observation with ocean HF radar.

  Zhang, W., N. Ebuchi, Y. Fukamachi, F. Cheng, K. I. Ohshima, B. Emery, T. Toyota, H. Abe, K. Shirasawa

  IEEE Transactions of Geoscience and Remote Sensing 58 1 378 - 390 2020年01月 [査読有り][通常論文]
  
• Favorable Conditions for Suspension Freezing in an Arctic Coastal Polynya

  Ito Masato, Ohshima Kay I, Fukamachi Yasushi, Hirano Daisuke, Mahoney Andrew R, Jones Joshua, Takatsuka Toru, Eicken Hajo

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 124 12 8701 - 8719 2019年12月08日 [査読有り][通常論文]
   

  Arctic sea ice incorporates and transports sediment, releasing it back into the water column during the melting season. This process constitutes an important aspect of marine sediment transport and biogeochemical cycling. Sediment incorporation into sea ice is considered to occur mainly through underwater interaction between frazil ice and resuspended sediment, referred to as suspension freezing. However, harsh environmental conditions have greatly limited field observations of this phenomenon. Analysis of mooring data from a coastal polynya in the northeastern Chukchi Sea, in conjunction with coastal ice radar and meteorological data, indicates that suspension freezing is a key mechanism for sediment entrainment into sea ice. During polynya episodes, acoustic backscatter data obtained by an Acoustic Doppler Current Profiler showed the presence of frazil ice from the surface down to 20- to 25-m depth, coinciding with in situ and potential supercooling. Underwater frazil ice persisted over 1 week under windy, turbulent water column conditions. A combination of the turbidity and Acoustic Doppler Current Profiler backscatter data revealed upward sediment dispersion associated with strong currents during the polynya episodes. The fact that frazil ice and resuspended sediment were detected at the same depth and time strongly suggests the interaction between ice crystals and sediment particles, that is, suspension freezing.
• Sea Ice Observation With Oceanographic HF Radar

  Zhang, W, N. Ebuchi, Y. Fukamachi, F. Cheng, K. I. Ohshima, B. Emery, T. Toyota, H. Abe, K. Shirasawa

  IEEE Transactions on Geoscience and Remote Sensing 58 1 1 - 13 2019年09月 [査読有り][通常論文]
   

  © 1980-2012 IEEE. High-frequency (HF) ocean radar has the potential to observe sea ice, but this application has not been thoroughly investigated. In this article, we explore sea ice observation with HF radar (HFR) and develop a corresponding signal processing procedure. We derived sea ice radial velocities from raw HFR data and determined angular positions using the MUltiple SIgnal Classification (MUSIC) algorithm. Sea ice velocities were evaluated by comparison with measurements from moored acoustic Doppler current profilers (ADCPs) and a drifting buoy. The root-mean-square (rms) differences between the sea ice velocities obtained by HFR and the ADCPs decreased with increasing radar signal-to-noise ratio (SNR), implying that a high SNR was associated with accurate measurement of sea ice velocity. These results agree with previous validations of HFR ocean current observations. The sea ice pattern mapped by HFR is consistent with the simultaneous C-band microwave radar observations. In particular, the HFR captured the approach of the sea ice edge toward the coast. Sharp attenuation of the HF signal over high concentration sea ice resulted in missing and/or low-SNR data at ranges beyond the front edge of pack ice, in qualitative agreement with model estimates of attenuation.
• Evaluation of AMSR-E Thin Ice Thickness Algorithm from a Mooring-Based Observation: How Can the Satellite Observe a Sea Ice Field with Nonuniform Thickness Distribution?

  Kashiwase, H, K. I. Ohshima, Y. Fukamachi, S. Nihashi, T. Tamur

  Journal of Atmospheric and Oceanic Technology 36 8 1623 - 1641 2019年08月 [査読有り][通常論文]
   

  The quantification of sea ice production in coastal polynyas is a key issue to understand the global climate system. In this study, we directly compared Advanced Microwave Scanning Radiometer-EOS (AMSR-E) data with the sea ice thickness distribution obtained from a mooring observation during the winter of 2003 off Sakhalin in the Sea of Okhotsk to evaluate the algorithm for estimation of sea ice thickness in coastal polynyas. By using thermal ice thickness as a target physical quantity, we found that the obtained relationship between the polarization ratio (PR) and ice thickness can provide an appropriate AMSR-E algorithm to estimate thin ice thickness, irrespective of the uniform or nonuniform ice thickness field. The relationship between the PR value and thermal ice thickness is likewise consistent with the local PR–thickness relationship that is observed at individual ice floes. This is because both the PR value and thermal ice thickness are more sensitive to thinner ice. Furthermore, we evaluated the method for detection of active frazil in a coastal polynya by comparing with the mooring data, and subsequently modified it to classify the coastal polynya into three thin ice types, namely, active frazil, thin solid ice, and mixed ice (mixture of active frazil and thin solid ice). The improved algorithm successfully represents the thermal ice thickness even for a relatively small-scale polynya off Sakhalin and is expected to be useful for better quantification of sea ice production in the global ocean owing to its high versatility.
• Instantaneous sea ice drift speed from TanDEM-X interferometry

  Dyre Oliver Dammann, Leif E. B. Eriksson, Joshua M. Jones, Andrew R. Mahoney, Roland Romeiser, Franz J. Meyer, Hajo Eicken, Yasushi Fukamachi

  The Cryosphere 13 1395 - 1408 2019年04月 [査読有り][通常論文]
  
• Activities to promote industry-government-academia collaborative research on the Arctic Region supported by Japan Arctic Research Network Center (J-ARC Net)

  Tanaka, M, Y. Fukamachi, S. Tanaka, S. Saitoh

  Proceedings of the 34th International Symposium on the Okhotsk Sea & Polar Oceans 2019 167 - 170 2019年02月 [査読無し][通常論文]
  
• Study on Oil Spill Response Technology in Cold Water Condition - Lessons learned from Exxon Valdes and Deepwater Horizon -

  Nakazawa, N, H. Yamaguchi, A. Kurokawa, J. Ono, T. Terashima, G. Sagawa, S. Yano, Y. Fukamachi, K. I. Ohshima

  Proceedings of the 34th International Symposium on the Okhotsk Sea & Polar Oceans 2019 190 - 192 2019年02月 [査読無し][通常論文]
  
• Arctic Technology Research Forum to consolidate opinions form industry

  Kikuchi, T, H. Yamaguchi, H. Yoshinaga, S. Fukuba, M. Miwa, T. Kashiwagi, H. Yoshida, K. I. Ohshima, Y. Fukamachi, H. Yabuki, Y. Kodama

  Proceedings of the 34th International Symposium on the Okhotsk Sea & Polar Oceans 2019 171 - 175 2019年02月 [査読無し][通常論文]
  
• Year-round observations of sea-ice drift and near-inertial internal waves in the Northwind Abyssal Plain, Arctic Ocean

  Kawaguchi, Y, M. Itoh, Y. Fukamachi, E. Moriya, J. Onodera, T. Kikuchi, N. Harada

  Polar Science 21 212 - 223 2019年01月 [査読有り][通常論文]
  
• Winter Water Formation in Coastal Polynyas of the Eastern Chukchi Shelf: Pacific and Atlantic Influences

  Daisuke Hirano, Yasushi Fukamachi, Kay I. Ohshima, Eiji Watanabe, Andrew R. Mahoney, Hajo Eicken, Motoyo Itoh, Daisuke Simizu, Katsushi Iwamoto, Joshua Jones, Toru Takatsuka, Takashi Kikuchi, Takeshi Tamura

  Journal of Geophysical Research: Oceans 123 8 5688 - 5705 2018年08月 [査読有り][通常論文]
   

  ©2018. American Geophysical Union. All Rights Reserved. Water properties and formation processes of Alaskan Coastal Winter Water (ACWW) over the eastern Chukchi shelf along the Alaska coast, the so-called Barrow Canyon pathway, are examined using data from moorings, atmospheric reanalysis, satellite-derived sea-ice production (SIP), and a numerical tracer experiment. Along this pathway, Pacific Winter Water (PWW) can be modified to produce ACWW through SIP accompanied by production of cold, saline polynya water in the coastal polynyas, upwelling of warm Atlantic Water (AW), and mixing processes on the shelf. Three different types of ACWW are formed: (i) a mixture of AW and PWW, (ii) a mixture of AW and polynya water, and (iii) hypersaline polynya water. The northeasterly winds, correlated with the north-south atmospheric pressure gradient between Beaufort High and Aleutian Low, are common triggers of polynya SIP episodes and AW upwelling in the Barrow Coastal Polynya (BCP). Due to the dual impact of northeasterly winds, PWW modification processes in the BCP are more complicated than what occurs elsewhere in the Chukchi Polynya. The impact of AW upwelling on the ACWW formation is most prominent in the BCP, usually centered along the coast. All types of ACWW are thought to be basically transported westward or northwestward with the Chukchi slope current and/or Beaufort Gyre and finally contribute to maintenance of the lower halocline layer especially over the Chukchi Borderland, Northwind Ridge, and southern Canada Basin. Even in the Pacific sector of the Arctic Ocean, ACWW properties are strongly influenced by both Atlantic-origin and Pacific-origin waters.
• Monitoring of the Soya Warm Current by HF ocean radars since 2003.

  Ebuchi, N, Y. Fukamachi, K. I. Ohshima, T. Takatsuka, M. Ishikawa, K. Shirasawa, M. Wakatsuchi

  Proceedings of the 4th ORCA 2018年06月 [査読無し][通常論文]
  
• Upwelling of Macronutrients and Dissolved Inorganic Carbon by a Subglacial Freshwater Driven Plume in Bowdoin Fjord, Northwestern Greenland

  Naoya Kanna, Shin Sugiyama, Yoshihiko Ohashi, Daiki Sakakibara, Yasushi Fukamachi, Daiki Nomura

  Journal of Geophysical Research: Biogeosciences 123 5 1666 - 1682 2018年05月 [査読有り][通常論文]
  
• Sea-ice thickness in the coastal northeastern Chukchi Sea from moored ice-profiling sonar

  Yasushi Fukamachi, Daisuke Simizu, Kay I. Ohshima, Hajo Eicken, Andrew R. Mahoney, Katsushi Iwamoto, Erika Moriya, Sohey Nihashi

  JOURNAL OF GLACIOLOGY 63 241 888 - 898 2017年10月 [査読有り][通常論文]
   

  Time series ice-draft data were obtained from moored ice-profiling sonar (IPS), in the coastal northeastern Chukchi Sea during 2009/10. Time series data show seasonal growth of sea-ice draft, occasionally interrupted by coastal polynya. The sea-ice draft distribution indicates a slightly lower abundance of thick, deformed ice compared with the eastern Beaufort Sea. In January, a rapid increase in the abundance of thick ice coincided with a period of minimal drift indicating compaction again the coast and dynamical thickening. The overall mean draft and corresponding derived thickness are 1.27 and 1.38 m, respectively. The evolution of modal ice thickness observed can be explained mostly by thermodynamic growth. The derived ice thicknesses are used to estimate heat losses based on ERA-interim data. Heat losses from the raw, 1 s IPS data are similar to 50 and 100% greater than those calculated using IPS data averaged over spatial scales of similar to 20 and 100 km, respectively. This finding demonstrates the importance of subgrid-scale ice-thickness distribution for heat-loss calculation. The heat-loss estimate based on thin ice data derived from AMSR-E data corresponds well with that from the 1 s observed ice-thickness data, validating heat-loss estimates from the AMSR-E thin ice-thickness algorithm.
• Observations of frazil ice formation and upward sediment transport in the Sea of Okhotsk: A possible mechanism of iron supply to sea ice

  Masato Ito, Kay I. Ohshima, Yasushi Fukamachi, Genta Mizuta, Yoshimu Kusumoto, Jun Nishioka

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 122 2 788 - 802 2017年02月 [査読有り][通常論文]
   

  In the Sea of Okhotsk, sediment incorporation, transport and release by sea ice potentially plays important roles in the bio-related material (such as iron) cycle and ecosystem. The backscatter strength data of bottom-mounted Acoustic Doppler Current Profilers have suggested signals of frazil ice down to 30 m depth, and signals of upward sediment transport throughout the water column simultaneously in the region northeast of Sakhalin, with a water depth of similar to 100 m. Such events occurred under turbulent conditions with strong winds of 10-20 m s(-1). During such events, newly formed ice was present near the observational sites, shown by satellite microwave imagery. Sediment dispersion from the bottom occurred in association with strong currents of 1.0-1.5 m s(-1). During these events, the mixed layer reaches near the bottom due to wind-induced stirring, inferred from the high frequency component of vertical velocity. Thus the winter time turbulent mixing brings re-suspended sediment up to near the ocean surface. This study provides the first observational evidence of a series of processes on the incorporation of sedimentary materials into sea ice: sedimentary particles are dispersed by the strong bottom current, subsequently brought up to near the surface by winter time mixing, and finally incorporated into sea ice through underwater interaction with frazil ice and/ or flooding of sea ice floes. This wintertime incorporation of bottom sediment into sea ice is a possible mechanism of iron supply to sea ice which melts in spring, and releases bio-reactive iron into the ocean.
• Landfast sea ice breakouts: Stabilizing ice features, oceanic and atmospheric forcing at Barrow, Alaska

  Joshua Jones, Hajo Eicken, Andrew Mahoney, M. Rohith, Chandra Kambhamettu, Yasushi Fukamachi, Kay I. Ohshima, J. Craig George

  CONTINENTAL SHELF RESEARCH 126 50 - 63 2016年09月 [査読有り][通常論文]
   

  Landfast sea ice is an important seasonal feature along most Arctic coastlines, such as that of the Chukchi Sea near Barrow, Alaska. Its stability throughout the ice season is determined by many factors but grounded pressure ridges are the primary stabilizing component. Landfast ice breakouts occur when these grounded ridges fail or unground, and previously stationary ice detaches from the coast and drifts away. Using ground-based radar imagery from a coastal ice and ocean observatory at Barrow, we have developed a method to estimate the extent of grounded ridges by tracking ice motion and deformation over the course of winter and have derived ice keel depth and potential for grounding from cumulative convergent ice motion. Estimates of landfast ice grounding strength have been compared to the atmospheric and oceanic stresses acting on the landfast ice before and during breakout events to determine prevailing causes for the failure of stabilizing features. Applying this approach to two case studies in 2008 and 2010, we conclude that a combination of atmospheric and oceanic stresses may have caused the breakouts analyzed in this study, with the latter as the dominant force. Preconditioning (as weakening) of grounded ridges by sea level variations may facilitate failure of the ice sheet leading to breakout events. (C) 2016 Elsevier Ltd. All rights reserved.
• The suppression of Antarctic bottom water formation by melting ice shelves in Prydz Bay

  G. D. Williams, L. Herraiz-Borreguero, F. Roquet, T. Tamura, K. I. Ohshima, Y. Fukamachi, A. D. Fraser, L. Gao, H. Chen, C. R. McMahon, R. Harcourt, M. Hindell

  NATURE COMMUNICATIONS 7 2016年08月 [査読有り][通常論文]
   

  A fourth production region for the globally important Antarctic bottom water has been attributed to dense shelf water formation in the Cape Darnley Polynya, adjoining Prydz Bay in East Antarctica. Here we show new observations from CTD-instrumented elephant seals in 2011-2013 that provide the first complete assessment of dense shelf water formation in Prydz Bay. After a complex evolution involving opposing contributions from three polynyas (positive) and two ice shelves (negative), dense shelf water (salinity 34.65-34.7) is exported through Prydz Channel. This provides a distinct, relatively fresh contribution to Cape Darnley bottom water. Elsewhere, dense water formation is hindered by the freshwater input from the Amery and West Ice Shelves into the Prydz Bay Gyre. This study highlights the susceptibility of Antarctic bottom water to increased freshwater input from the enhanced melting of ice shelves, and ultimately the potential collapse of Antarctic bottom water formation in a warming climate.
• Sea ice observation by high frequency ocean radar in the southern Sea of Okhotsk.

  Zhang, W, H. Abe, N. Ebuchi, Y. Fukamachi, B. Emery, F. Cheng, Y. Xiao, K. Shirasawa

  Proceedings of Third Ocean Radar Conference for Asia 37 - 44 2016年04月 [査読無し][通常論文]
  
• Surface water mass composition changes captured by cores of Arctic land-fast sea ice

  I. J. Smith, H. Eicken, A. R. Mahoney, R. Van Hale, A. J. Gough, Y. Fukamachi, J. Jones

  CONTINENTAL SHELF RESEARCH 118 154 - 164 2016年04月 [査読有り][通常論文]
   

  In the Arctic, land-fast sea ice growth can be influenced by fresher water from rivers and residual summer melt. This paper examines a method to reconstruct changes in water masses using oxygen isotope measurements of sea ice cores. To determine changes in sea water isotope composition over the course of the ice growth period, the output of a sea ice thermodynamic model (driven with reanalysis data, observations of snow depth, and freeze-up dates) is used along with sea ice oxygen isotope measurements and an isotopic fractionation model. Direct measurements of sea ice growth rates are used to validate the output of the sea ice growth model. It is shown that for sea ice formed during the 2011/2012 ice growth season at Barrow, Alaska, large changes in isotopic composition of the ocean waters were captured by the sea ice isotopic composition. Salinity anomalies in the ocean were also tracked by moored instruments. These data indicate episodic advection of meteoric water, having both lower salinity and lower oxygen isotopic composition, during the winter sea ice growth season. Such advection of meteoric water during winter is surprising, as no surface meltwater and no local river discharge should be occurring at this time of year in that area. How accurately changes in water masses as indicated by oxygen isotope composition can be reconstructed using oxygen isotope analysis of sea ice cores is addressed, along with methods/strategies that could be used to further optimize the results. The method described will be useful for winter detection of meteoric water presence in Arctic fast ice regions, which is important for climate studies in a rapidly changing Arctic. Land-fast sea ice effective fractionation coefficients were derived, with a range of +1.82 parts per thousand to +2.52 parts per thousand. Those derived effective fractionation coefficients will be useful for future water mass component proportion calculations. In particular, the equations given can be used to inform choices made when engaging in end member determination for working out the component proportions of water masses. (C) 2016 Elsevier Ltd. All rights reserved.
• Estimation of wind drift current in the Soya Strait

  Wei Zhang, Naoto Ebuchi, Yasushi Fukamachi, Yutaka Yoshikawa

  JOURNAL OF OCEANOGRAPHY 72 2 299 - 311 2016年04月 [査読有り][通常論文]
   

  Three high-frequency (HF) ocean radars were deployed around the Soya (La P,rouse) Strait in 2003 to monitor the Soya Warm Current (SWC). Surface current observed by the HF radars contains a wind drift component, which must be removed in order to estimate the interior SWC. The wind drift parameters, speed factor and turning angle were derived from the surface current measured by the HF radars, the vertical current profile measured by a bottom-mounted acoustic Doppler current profiler (ADCP), and wind data from the numerical weather analysis system operated by the Japan Meteorological Agency (JMA) from October 1, 2006 to July 24, 2008. The ensemble-mean turning angle and speed factor from the entire dataset (excluding August 2007) were estimated to be 28A degrees and 0.66 %, respectively. No significant seasonal variations were discernible in the wind drift parameters. After removal of the wind drift current estimated from the wind with the ensemble-mean drift parameters, the correlation coefficient between the along-shore current speed and sea level difference between the Sea of Japan and Sea of Okhotsk improved from 0.791 to 0.825. It was revealed that the magnitude of wind drift current reaches 45 % of that of the interior current in winter and approximately 20 % in summer, indicating the importance of wind drift current estimation in this region.
• Interannual variability in sea-ice thickness in the pack-ice zone off Lutzow-Holm Bay, East Antarctica

  Fuko Sugimoto, Takeshi Tamura, Haruhito Shimoda, Shotaro Uto, Daisuke Simizu, Kazutaka Tateyama, Seita Hoshino, Toshihiro Ozeki, Yasushi Fukamachi, Shuki Ushio, Kay I. Ohshima

  POLAR SCIENCE 10 1 43 - 51 2016年03月 [査読有り][通常論文]
   

  Under the Japanese Antarctic Research Expedition (JARE) program, sea-ice thickness has been routinely monitored off Lutzow-Holm Bay (East Antarctica) during the summer (mid-December to early January) since 2000/01, using an electromagnetic induction (EM) instrument onboard the icebreaker Shirase. Analysis of these data over a 10-year period, combined with visual observations using a simplified form of the ASPeCt (Antarctic Sea ice Processes and Climate) protocol, suggests a strong interannual variability in sea-ice thickness in this region. For the repeat pack-ice observation area, where the sea-ice thickness averaged over the nine seasons is similar to 1.9 m, mean thicknesses of observed sea-ice in 2010/11 and 2011/12 are exceptionally large, at similar to 3.3 and similar to 5.8 m, respectively. This result is strongly related to regional patterns of sea ice dynamics. Ice convergence caused by anomalous northerly winds was particularly high in 2011/12, suggesting that the extremely thick ice observed in that season resulted largely from sea-ice deformation processes (including pressure ridging). Longer-term analysis of data from the past 34 years confirms that sea-ice conditions and thickness off Lutzow-Holm Bay in summer are determined mainly by the large-scale pattern of atmospheric pressure in December. (C) 2015 Elsevier B.V. and NIPR. All rights reserved.
• Observations of frazil ice formation and sediment upward transport off the northeast coast of Sakhalin

  Ito, M, K. I. Ohshima, J. Nishioka, Y. Kusumoto, Y. Fukamachi

  Proceedings of the 31th International Symposium on Okhotsk Sea & Sea Ice 124 - 127 2016年02月 [査読無し][通常論文]
  
• A wind-driven, hybrid latent and sensible heat coastal polynya off Barrow, Alaska

  Daisuke Hirano, Yasushi Fukamachi, Eiji Watanabe, Kay I. Ohshima, Katsushi Iwamoto, Andrew R. Mahoney, Hajo Eicken, Daisuke Simizu, Takeshi Tamura

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 121 1 980 - 997 2016年01月 [査読有り][通常論文]
   

  The nature of the Barrow Coastal Polynya (BCP), which forms episodically off the Alaska coast in winter, is examined using mooring data, atmospheric reanalysis data, and satellite-derived sea-ice concentration and production data. We focus on oceanographic conditions such as water mass distribution and ocean current structure beneath the BCP. Two moorings were deployed off Barrow, Alaska in the northeastern Chukchi Sea from August 2009 to July 2010. For sea-ice season from December to May, a characteristic sequence of five events associated with the BCP has been identified; (1) dominant northeasterly wind parallel to the Barrow Canyon, with an offshore component off Barrow, (2) high sea-ice production, (3) upwelling of warm and saline Atlantic Water beneath the BCP, (4) strong up-canyon shear flow associated with displaced density surfaces due to the upwelling, and (5) sudden suppression of ice growth. A baroclinic current structure, established after the upwelling, caused enhanced vertical shear and corresponding vertical mixing. The mixing event and open water formation occurred simultaneously, once sea-ice production had stopped. Thus, mixing events accompanied by ocean heat flux from the upwelled warm water into the surface layer played an important role in formation/maintenance of the open water area (i.e., sensible heat polynya). The transition from a latent to a sensible heat polynya is well reproduced by a high-resolution pan-Arctic ice-ocean model. We propose that the BCP, previously considered to be a latent heat polynya, is a wind-driven hybrid latent and sensible heat polynya, with both features caused by the same northeasterly wind.
• Water properties, heat and volume fluxes of Pacific water in Barrow Canyon during summer 2010

  Motoyo Itoh, Robert S. Pickart, Takashi Kikuchi, Yasushi Fukamachi, Kay I. Ohshima, Daisuke Simizu, Kevin R. Arrigo, Svein Vagle, Jianfeng He, Carin Ashjian, Jeremy T. Mathis, Shigeto Nishino, Carolina Nobre

  DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 102 43 - 54 2015年08月 [査読有り][通常論文]
   

  Over the past few decades, sea ice retreat during summer has been enhanced in the Pacific sector of the Arctic basin, likely due in part to increasing summertime heat flux of Pacific-origin water from the Bering Strait. Barrow Canyon, in the northeast Chukchi Sea, is a major conduit through which the Pacific-origin water enters the Arctic basin. This paper presents results from 6 repeat high-resolution shipboard hydrographic/velocity sections occupied across Barrow Canyon in summer 2010. The different Pacific water masses feeding the canyon - Alaskan coastal water (ACW), summer Bering Sea water (BSW), and Pacific winter water (PWW) - all displayed significant intra-seasonal variability. Net volume transports through the canyon were between 0.96 and 1.70 Sv poleward, consisting of 0.41-0.98 Sv of warm Pacific water (ACW and BSW) and 0.28-0.65 Sv of PWW. The poleward heat flux also varied strongly, ranging from 8.56 TW to 24.56 TW, mainly due to the change in temperature of the warm Pacific water. Using supplemental mooring data from the core of the warm water, along with wind data from the Pt. Barrow weather station, we derive and assess a proxy for estimating heat flux in the canyon for the summer time period, which is when most of the heat passes northward towards the basin. The average heat flux for 2010 was estimated to be 3.34 TW, which is as large as the previous record maximum in 2007. This amount of heat could melt 315,000 km(2) of 1-meter thick ice, which likely contributed to significant summer sea ice retreat in the Pacific sector of the Arctic Ocean. (C) 2015 The Authors. Published by Elsevier Ltd.
• The role of turbulent mixing in the modified Shelf Water overflows that produce Cape Darnley Bottom Water

  Daisuke Hirano, Yujiro Kitade, Kay I. Ohshima, Yasushi Fukamachi

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 120 2 910 - 922 2015年02月 [査読有り][通常論文]
   

  The mixing process associated with modified Shelf Water (mSW) overflows that eventually mix to form Cape Darnley Bottom Water (CDBW) was investigated by hydrographic and microstructure observations off the Cape Darnley Polynya (CDP), East Antarctica, in January 2009. Closely spaced microstructure observations revealed that mSW properties varied considerably within a distance of similar to 4 km across the shelf edge. Near the bottom, the rate of turbulent kinetic energy dissipation was enhanced to values greater than 1027 W kg(-1), and the vertical scale of the bottom boundary layer (BBL) was on the order of 10 m. The observed BBL around the shelf edge was characterized by strong vertical mixing with turbulent eddy diffusivities of similar to O(102321022) m(2) s(-1). A geostrophically balanced density current, which resulted from the presence of mSW over the continental shelf, is considered the primary energy source for the turbulent mixing in the BBL. This turbulent mixing transforms the overflowing mSW through mixing with ambient water masses, specifically with the overlying modified Circumpolar Deep Water. The BBL is also thought to partly contribute to the gradual descent of mSW down the continental slope through bottom Ekman transport. We conclude that turbulent mixing, primarily caused by a density current, plays an important role in CDBW formation, by modifying the mSW overflowing from the CDP.
• Taking a look at both sides of the ice: comparison of ice thickness and drift speed as observed from moored, airborne and shore-based instruments near Barrow, Alaska

  Andrew R. Mahoney, Hajo Eicken, Yasushi Fukamachi, Kay I. Ohshima, Daisuke Simizu, Chandra Kambhamettu, M. V. Rohith, Stefan Hendricks, Joshua Jones

  ANNALS OF GLACIOLOGY 56 69 363 - 372 2015年 [査読有り][通常論文]
   

  Data from the Seasonal Ice Zone Observing Network (SIZONet) acquired near Barrow, Alaska, during the 2009/10 ice season allow novel comparisons between measurements of ice thickness and velocity. An airborne electromagnetic survey that passed over a moored Ice Profiling Sonar (IPS) provided coincident independent measurements of total ice and snow thickness and ice draft at a scale of 10 km. Once differences in sampling footprint size are accounted for, we reconcile the respective probability distributions and estimate the thickness of level sea ice at 1.48 +/- 0.1 m, with a snow depth of 0.12 +/- 0.07 m. We also complete what we believe is the first independent validation of radar-derived ice velocities by comparing measurements from a coastal radar with those from an under-ice acoustic Doppler current profiler (ADCP). After applying a median filter to reduce high-frequency scatter in the radar-derived data, we find good agreement with the ADCP bottom-tracked ice velocities. With increasing regulatory and operational needs for sea-ice data, including the number and thickness of pressure ridges, coordinated observing networks such as SIZONet can provide the means of reducing uncertainties inherent in individual datasets.
• Observations of supercooled water and frazil ice formation in an Arctic coastal polynya from moorings and satellite imagery

  Masato Ito, Kay I. Ohshima, Yasushi Fukamachi, Daisuke Simizu, Katsushi Iwamoto, Yoshimasa Matsumura, Andrew R. Mahoney, Hajo Eicken

  ANNALS OF GLACIOLOGY 56 69 307 - 314 2015年 [査読有り][通常論文]
   

  Formation of supercooled water and frazil ice was studied in the Chukchi Sea coastal polynya off Barrow, Alaska, USA, in winter 2009/10, using moored salinity/temperature sensors and Ice Profiling Sonar (IPS) data along with satellite data. Oceanographic data from two moorings revealed episodic events of potential supercooling at 30-40 m depth, including the possibility of in situ supercooling, while the polynya was open. We identified frazil ice-like signals in the IPS data down to 5-15 m depth, associated with large heat loss and windy, turbulent conditions in an active polynya. This likely represents the first IPS observation of frazil ice in the marine environment. On the day of the maximum signal of frazil ice, spaceborne synthetic aperture radar shows streaks of high backscatter within the polynya, indicating active frazil ice formation just downwind of the mooring sites. In addition, the longer-term potential supercooling that persisted for 1-3 weeks occurred twice despite the absence of polynya activity at the mooring sites. These events occurred during periods dominated by the northeastward current. A series of coastal polynyas had formed southwest of the mooring sites prior to these events. Thus, the water masses with potential supercooling were likely advected from these polynyas.
• A Numerical Investigation of Formation and Variability of Antarctic Bottom Water off Cape Darnley, East Antarctica

  Yoshihiro Nakayama, Kay I. Ohshima, Yoshimasa Matsumura, Yasushi Fukamachi, Hiroyasu Hasumi

  JOURNAL OF PHYSICAL OCEANOGRAPHY 44 11 2921 - 2937 2014年11月 [査読有り][通常論文]
   

  At several locations around Antarctica, dense water is formed as a result of intense sea ice formation. When this dense water becomes sufficiently denser than the surrounding water, it descends the continental slope and forms Antarctic Bottom Water (AABW). This study presents the AABW formation off the coast of Cape Darnley [Cape Darnley Bottom Water (CDBW)] in East Antarctica, using a nonhydrostatic model. The model is forced for 8 months by a temporally uniform surface salt flux (because of sea ice formation) estimated from Advanced Microwave Scanning Radiometer for Earth Observing System (EOS; AMSR-E) data and a heat budget calculation. The authors reproduce AABW formation and associated periodic downslope flows of dense water. Descending pathways of dense water are largely determined by the topography; most dense water flows into depressions on the continental shelf, advects onto the continental slope, and is steered downslope to greater depths by the canyons. Intense sea ice formation is the most important factor in the formation of AABW off Cape Darnley, and the existence of depressions is of only minor importance for the flux of CDBW. The mechanism responsible for the periodic downslope flow of dense water is further analyzed using an idealized model setup. The period of dense water outflow is regulated primarily by the topographic beta effect.
• What drives the southward drift of sea ice in the Sea of Okhotsk?

  Daisuke Simizu, Kay I. Ohshima, Jun Ono, Yasushi Fukamachi, Genta Mizuta

  PROGRESS IN OCEANOGRAPHY 126 33 - 43 2014年08月 [査読有り][通常論文]
   

  The Sea of Okhotsk is the southernmost sea-ice zone with sizable ice. It is widely believed that the prevailing northwesterly wind and the southward East Sakhalin Current (ESC) are the two main factors that drive the southward drift of sea ice. However, the relative contributions of these factors have not been understood. In this paper, by using the current and ice-drift data measured with the moored Acoustic Doppler Current Profiler, a 3-D ocean model simulation, objective analysis data of the wind, and satellite sea-ice data, we examine to what degree and how the ice drift is determined by the wind and ocean current. From a linear regression of the observed ice drift, ocean current, and wind, the wind-forced component of the ice drift was best fitted when sea ice is assumed to move with a speed of 1.6% of the geostrophic wind with a turning angle of 17.6 degrees to the left of the wind. Such a relationship was adopted as the wind-drift component for all sea-ice pixels detected from Special Sensor Microwave Imager data. For the ocean-forced component of the ice drift, we adopted the current at 20 m depth from a numerical model simulation that reproduces well the ESC and its variability. We then evaluated the sea-ice drift over 46-54 degrees N during 1998-2005. For the southward drift of sea ice, the contribution of the wind component is found to be larger than the oceanic component, although the ocean contribution becomes larger, typically comparable to the wind contribution, near the coast and in the northern region where the ESC is stronger. We estimated the average annual cumulative southward ice transport to be 3.0 +/- 0.9 x 10(11) m(3) at 53 degrees N. This ice transport is comparable to the annual discharge of the Amur River. The ratio of wind to oceanic components in the transport is estimated to be similar to 1.2-1.8. We also conducted ice-drift simulations based on the modeled current velocity and the assumed wind drift of 1.5% geostrophic wind with a turning angle of 15 degrees to the left. The simulations reproduce well the ice drift north of 47 degrees N but not south of 47 degrees N, likely due to the poor representation of the current system at the latter, underevaluation of the wind factor near the ice edges, and the neglect of ice formation and melt. (C) 2014 Elsevier Ltd. All rights reserved.
• Antarctic Bottom Water production from the Vincennes Bay Polynya, East Antarctica

  Yujiro Kitade, Keishi Shimada, Takeshi Tamura, Guy D. Williams, Shigeru Aoki, Yasushi Fukamachi, Fabien Roquet, Mark Hindell, Shuki Ushio, Kay I. Ohshima

  GEOPHYSICAL RESEARCH LETTERS 41 10 3528 - 3534 2014年05月 [査読有り][通常論文]
   

  One year moorings at depths greater than 3000m on the continental slope off Vincennes Bay, East Antarctica, reveal the cold (<-0.5 degrees C) and fresh (<34.64) signals of newly formed Antarctic Bottom Water (AABW). The signal appeared in June, 3 months after the onset of active sea-ice production in the nearby Vincennes Bay Polynya (VBP). The AABW signal continued for about 5 months at two moorings, with 1 month delay at the western site further downstream. Ship-based hydrographic data are in agreement, detecting the westward spread of new AABW over the continental slope from VBP. On the continental shelf, Dense Shelf Water (DSW) formation is observed by instrumented seals, in and around the VBP during autumn, and we estimate its transport to be 0.16 +/- 0.07 (x 106m3s-1). We conclude that the DSW formed in this region, albeit from a modest amount of sea-ice production, nonetheless contributes to the upper layer of AABW in Australian-Antarctic Basin.
• Estimation of wind drift current in the Soya Strait.

  Zhang, W, N. Ebuchi, Y. Fukamachi, Y. Yoshikawa

  Proceedings of Second Ocean Radar Conference for Asia 68 - 71 2014年04月 [査読無し][通常論文]
  
• Antarctic Bottom Water production by intense sea-ice formation in the Cape Darnley polynya

  Kay I. Ohshima, Yasushi Fukamachi, Guy D. Williams, Sohey Nihashi, Fabien Roquet, Yujiro Kitade, Takeshi Tamura, Daisuke Hirano, Laura Herraiz-Borreguero, Iain Field, Mark Hindell, Shigeru Aoki, Masaaki Wakatsuchi

  Nature Geoscience 6 3 235 - 240 2013年03月 [査読有り][通常論文]
   

  The formation of Antarctic Bottom Water-the cold, dense water that occupies the abyssal layer of the global ocean-is a key process in global ocean circulation. This water mass is formed as dense shelf water sinks to depth. Three regions around Antarctica where this process takes place have been previously documented. The presence of another source has been identified in hydrographic and tracer data, although the site of formation is not well constrained. Here we document the formation of dense shelf water in the Cape Darnley polynya (65°-69°E) and its subsequent transformation into bottom water using data from moorings and instrumented elephant seals (Mirounga leonina). Unlike the previously identified sources of Antarctic Bottom Water, which require the presence of an ice shelf or a large storage volume, bottom water production at the Cape Darnley polynya is driven primarily by the flux of salt released by sea-ice formation. We estimate that about 0.3-0.7 × 106 m3 s-1 of dense shelf water produced by the Cape Darnley polynya is transformed into Antarctic Bottom Water. The transformation of this water mass, which we term Cape Darnley Bottom Water, accounts for 6-13% of the circumpolar total. Copyright © 2013 Macmillan Publishers Limited.
• A method for predicting the occurrence of paralytic shellfish poisoning along the coast of Hokkaido in the Okhotsk Sea in summer

  Hiroshi Shimada, Mayumi Sawada, Iori Tanaka, Hiroki Asami, Yasushi Fukamachi

  FISHERIES SCIENCE 78 4 865 - 877 2012年07月 [査読有り][通常論文]
   

  To design a method for predicting outbreaks of paralytic shellfish poisoning (PSP) in scallop fishing grounds, the relationship between the distribution of the toxic dinoflagellate Alexandrium tamarense and the dynamics of the Soya Warm Current (SWC) was examined in the Okhotsk Sea off Hokkaido. Surveys were conducted from May to June to clarify the transportation mechanism of A. tamarense from the oceanic area to the coastal area. The sea-level difference (SLD) between Wakkanai and Abashiri was monitored as an index of the strength of the SWC southeastward flow in an alongshore belt to examine the possible occurrence of A. tamarense in the coastal area during temporal weakening of the SWC. A bottom-mounted acoustic Doppler current profiler (ADCP) was used for direct observations of the SWC. The results indicated that PSP occurred when low-salinity water contaminated with A. tamarense extended to the coast during temporal weakening of the SWC due to a decrease of the SLD. Our results strongly indicate that predictions can be realized by monitoring the decrease of SLD as an index of temporal weakening of the SWC after surveys of the distribution of A. tamarense in the oceanic area before the period of PSP occurrence.
• A treatise on frequency spectrum of drift ice velocity

  Matti Lepparanta, Annu Oikkonen, Kunio Shirasawa, Yasushi Fukamachi

  COLD REGIONS SCIENCE AND TECHNOLOGY 76-77 83 - 91 2012年06月 [査読有り][通常論文]
   

  Sea ice dynamics is examined for the frequency spectra of ice velocity using mathematical models and ice motion data. The data are from the Baltic Sea and Sea of Okhotsk. A general spectrum for linear coupled ice-ocean free drift is derived and analysed. Interior dynamics shows singularity in the Coriolis (inertial) frequency and asymptotic high frequency power law of -2. In the presence of internal friction the spectrum is expected to evenly fall to zero with frictional resistance increasing above yield level. In the observations, the main spectral peak is wide at the synoptic time scales. The Okhotsk Sea spectra show inertial and tidal signals but they are missing from the Baltic Sea due to very weak tides and shallow depth damping inertial oscillations. Above semidiurnal frequency ice velocity spectra fall in power law of -5/3, inherited from atmospheric and oceanic dynamics, and at very high frequencies, above 0.5 cph (cycles per hour) the fall seems to slow down to power law below -1. The Eulerian ice velocity spectrum was higher than the Lagrangian spectrum throughout the entire obtained spectrum (0.1-5 cpd (cycles per day)). Theoretical spectra show general agreement with observations except that they have less kinetic energy at very high frequencies and much stronger inertial peak. Thus Eulerian observations are more variable than Lagrangian observations. (C) 2012 Elsevier B.V. All rights reserved.
• Continuous observation of the Soya Warm Current by HF ocean radar since 2003.

  Ebuchi, N, Y. Fukamachi, K. I. Ohshima, M. Wakatsuchi

  Proceedings of First Ocean Radar Conference for Asia 82 - 86 2012年05月 [査読無し][通常論文]
  
• Coastal landfast sea ice decay and breakup in northern Alaska: Key processes and seasonal prediction

  Chris Petrich, Hajo Eicken, Jing Zhang, Jeremy Krieger, Yasushi Fukamachi, Kay I. Ohshima

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 117 doi:10.1029/2011JC007339  2012年02月 [査読有り][通常論文]
   

  Seasonal breakup of landfast sea ice consists of movement and irreversible ice detachment in response to winds or oceanic forces in the late stages of ice decay. The breakup process of landfast sea ice in the Chukchi Sea at Barrow, Alaska, was analyzed for the years 2000 through 2010 on the basis of local observations of snow and ice conditions, weather records, image sequences obtained from cameras, coastal X band marine radar, and satellite imagery. We investigated the relation of breakup to winds, tides, and nearshore current measurements from a moored acoustic Doppler current profiler. Two breakup modes are distinguished at Barrow on the basis of the degree of ice decay. Mechanical breakup due to wind and oceanic forces follows ablation and weakening of the ice. Thermal breakup is the result of ice disintegration under melt ponds, requiring little force to induce dispersion. Grounded pressure ridges are pivotal in determining the breakup mode. The timing of thermal breakup of the nearshore ice cover was found to correlate with the measured downwelling solar radiation in June and July. This linkage allows for the development of an operational forecast of landfast ice breakup. Results from forecasts during 2 years demonstrate that thermal breakup can be predicted to within a couple of days 2 weeks in advance. The cumulative shortwave energy absorbed by the ice cover provides for a measure of the state of ice decay and potential for disintegration. Discriminating between the two modes of breakup bears the potential to greatly increase forecasting skill.
• Enhancement of Sea Ice Drift due to the Dynamical Interaction between Sea Ice and a Coastal Ocean

  Yoshihiro Nakayama, Kay I. Ohshima, Yasushi Fukamachi

  JOURNAL OF PHYSICAL OCEANOGRAPHY 42 1 179 - 192 2012年01月 [査読有り][通常論文]
   

  Wind factor, the ratio of sea ice drift speed to surface wind speed, is a key factor for the dynamics of sea ice and is generally about 2%. In some coastal oceans, however, the wind factor tends to be larger near the coast. This study proposes the enhancement mechanism of the sea ice drift caused by the dynamical coupling between sea ice and a coastal ocean. In a coastal ocean covered with sea ice, wind-forced sea ice drift excites coastal trapped waves (shelf waves) and generates fluctuating ocean current. This ocean current can enhance sea ice drift when the current direction is the same as that of the wind-driven drift. The authors consider a simplified setting where spatially uniform oscillating wind drifts sea ice parallel to the coast. When a barotropic long shelf wave is assumed for the ocean response, sea ice drifts driven by wind and ocean are obtained analytically. The ratio of ocean-driven to wind-driven sea ice drifts is used for the evaluation of the oceanic contribution to the enhancement of sea ice drift. The enhancement is mostly determined by the characteristics of the shelf waves, and sea ice drift is significantly enhanced close to the coast with lower-frequency wind forcing. Comparison with the observation off the Sakhalin coast shows that the degree of enhancement of sea ice drift and its characteristic such that larger enhancement occurs near the coast are mostly consistent with our theoretical solution, suggesting that this mechanism is present in the real ocean.
• Coastal landfast sea ice decay and breakup in northern Alaska: Key processes and seasonal prediction

  Chris Petrich, Hajo Eicken, Jing Zhang, Jeremy Krieger, Yasushi Fukamachi, Kay I. Ohshima

  Journal of Geophysical Research: Oceans 117 2 2012年 [査読有り][通常論文]
   

  Seasonal breakup of landfast sea ice consists of movement and irreversible ice detachment in response to winds or oceanic forces in the late stages of ice decay. The breakup process of landfast sea ice in the Chukchi Sea at Barrow, Alaska, was analyzed for the years 2000 through 2010 on the basis of local observations of snow and ice conditions, weather records, image sequences obtained from cameras, coastal X band marine radar, and satellite imagery. We investigated the relation of breakup to winds, tides, and nearshore current measurements from a moored acoustic Doppler current profiler. Two breakup modes are distinguished at Barrow on the basis of the degree of ice decay. Mechanical breakup due to wind and oceanic forces follows ablation and weakening of the ice. Thermal breakup is the result of ice disintegration under melt ponds, requiring little force to induce dispersion. Grounded pressure ridges are pivotal in determining the breakup mode. The timing of thermal breakup of the nearshore ice cover was found to correlate with the measured downwelling solar radiation in June and July. This linkage allows for the development of an operational forecast of landfast ice breakup. Results from forecasts during 2 years demonstrate that thermal breakup can be predicted to within a couple of days 2 weeks in advance. The cumulative shortwave energy absorbed by the ice cover provides for a measure of the state of ice decay and potential for disintegration. Discriminating between the two modes of breakup bears the potential to greatly increase forecasting skill. Copyright 2012 by the American Geophysical Union.
• Sea-ice drift characteristics revealed by measurement of acoustic Doppler current profiler and ice-profiling sonar off Hokkaido in the Sea of Okhotsk

  Yasushi Fukamachi, Kay I. Ohshima, Yuji Mukai, Genta Mizuta, Masaaki Wakatsuchi

  ANNALS OF GLACIOLOGY 52 57 1 - 8 2011年 [査読有り][通常論文]
   

  In the southwestern part of the Sea of Okhotsk off Hokkaido, sea-ice drift characteristics are investigated using the ice and water velocities obtained from a moored upward-looking acoustic Doppler current profiler (ADCP) during the winters of 1999-2001. Using hourly-mean values of these data along with the wind data measured at a nearby coastal station, the wind factor and turning angle of the relative velocity between the ice and water velocities with respect to the wind are calculated assuming free drift under various conditions. Since the simultaneous sea-ice draft data are also available from a moored ice-profiling sonar (IPS), we examine the dependence of drift characteristics on ice thickness for the first time. As ice thickness increases and wind decreases, the wind factor decreases and the turning angle increases, as predicted by the theory of free drift. This study clearly shows the utility of the moored ADCP measurement for studying sea-ice drift, especially with the simultaneous IPS measurement for ice thickness, which cannot be obtained by other methods.
• Characteristics of sea ice in the Okhotsk coastal polynyas revealed by satellites, ice-profiling sonar and digital camera observations

  Sohey Nihashi, Naoto Ebuchi, Yasushi Fukamachi, Shuhei Takahashi

  ANNALS OF GLACIOLOGY 52 57 133 - 139 2011年 [査読有り][通常論文]
   

  The characteristics of ice in the Okhotsk coastal polynyas are examined. A map of AMSR-E thin-ice thickness in the northwest shelf region shows that most of the coastal polynya area is covered by thin ice with a thickness of 0.1 m. The thickness increases sharply at the edge of the polynya. From comparisons with QuikSCAT backscatter, the thin-ice area corresponds well with the low-backscatter area during almost all the coastal polynya period. A comparison with ice thickness measured by an ice-profiling sonar in the coastal polynya region of northeastern Sakhalin shows a similar relationship, with the backscatter tending to be low when the ice is thin. The averaged backscatter of thin (<= 0.1 m) ice is -19.6 +/- 2.8 dB (horizontal polarization). The backscatter of thin ice is considered to be mainly determined by the surface roughness because volume scattering of thin ice is low due to the dielectric properties associated with the high salinity. The results of this study suggest that the coastal polynya is covered with grease ice/nilas whose surface is almost mirror smooth. This is confirmed by a comparison with photographs taken at the coastal polynya region near Magadan, Russia. At the outer edge of the coastal polynya, a region of relatively high backscatter (>-16 dB),exists, probably because it has a rougher ice surface than the polynya area. This suggests that ice motion in this area may be convergent.
• Occurrence of blooms of the toxic dinoflagellate Alexandrium tamarense and paralytic shellfish poisoning infestation to scallops in the Okhotsk Sea off Hokkaido

  Hiroshi Shimada, Mayumi Sawada, Iori Tanaka, Hiroki Asami, Yasushi Fukamachi

  Nippon Suisan Gakkaishi (Japanese Edition) 77 3 439  2011年 [査読有り][通常論文]
  
• Volume Transport in the Soya Strait during 2006-2008

  Yasushi Fukamachi, Kay I. Ohshima, Naoto Ebuchi, Tadao Bando, Kazuya Ono, Minoru Sano

  JOURNAL OF OCEANOGRAPHY 66 5 685 - 696 2010年10月 [査読有り][通常論文]
   

  Time-series data of the vertical structure of the Soya Warm Current (SWC) were obtained by a bottom-mounted acoustic Doppler current profiler (ADCP) in the middle of the Soya Strait from September 2006 to July 2008. The site of the ADCP measurement was within the coverage of the ocean-radar measurement around the strait. The volume transport of the SWC through the strait is estimated on the basis of both the vertical structure observed by the ADCP and the horizontal structure observed by the radars for the first time. The annual transport estimates are 0.62-0.67 Sv (1 Sv = 10(6) m(3)s(-1)). They are somewhat smaller than the difference between the previous estimates of the inflow and outflow through other straits in the Sea of Japan, and smaller than those obtained in the region downstream of the strait during 2004-05 (0.94-1.04 Sv). The difference in the two periods may be attributed to interannual variability of the SWC and/or the different measurement locations.
• Propagation of subinertial variations in the Soya Warm Current revealed by HF ocean radars

  Ebuchi, N, Y. Fukamachi, K. I. Ohshima

  Proceedings of IGARSS 2010 3051 - 3054 2010年07月 [査読無し][通常論文]
  
• Strong export of Antarctic Bottom Water east of the Kerguelen plateau

  Y. Fukamachi, S. R. Rintoul, J. A. Church, S. Aoki, S. Sokolov, M. A. Rosenberg, M. Wakatsuchi

  NATURE GEOSCIENCE 3 5 327 - 331 2010年05月 [査読有り][通常論文]
   

  The primary paths for the transport of Antarctic Bottom Water from the Southern Ocean into the global ocean are the deep western boundary currents east of the Antarctic Peninsula and the Kerguelen plateau(1). Previous ship-based observations documented distinct water properties and velocities associated with a deep western boundary current in the Kerguelen region(2-7), but the mean flow is as yet unconstrained. Here we report measurements from a coherent array of eight current-meter moorings that reveal a narrow and intense equatorward flow extending throughout the water column just east of the Kerguelen plateau. Velocities averaged over two years exceed 20 cm s(-1) at depths of about 3,500 m, the strongest mean deep western boundary current flow yet observed at similar depths. We estimate the mean equatorward transport of water colder than 0 degrees C at 12.3 +/- 1.2 x 10(6) m(3) s(-1), partially compensated by poleward flow. We also estimate the net equatorward flow of water colder than 0.2 degrees C at about 8 x 10(6) m(3) s(-1), substantially higher than the 1.9 x 10(6) m(3) s(-1) reported from the boundary current that carries dense water from the Weddell Sea into the Atlantic Ocean north of the Falkland plateau(8). We conclude that the Kerguelen deep western boundary current is a significant pathway of the global ocean's deep overturning circulation.
• Southern Ocean Observing Systems (SOOS): Rationale and Strategy for Sustained Observations of the Southern Ocean

  Rintoul, S. R, K. Speer, M. Sparrow, M. Meredith, E. Hoffmann, E. Fahrbach, C. Summerhayes, A. Worby, M. England, R. Bellerby, S. Speich, D. Costa, J. Hall, M. Hindell, G. Hosie, K. Stansfield, Y. Fukamachi, T. de Bruin, A. Naveira Garabato, K. Alberson, V. Ryabinin, H. C. Shin, S. Gladyshev

  Proceedings of OceanObs '09: Sustained Ocean Observations and Information for Society (Vol. 2) WPP-306  2010年 [査読有り][通常論文]
  
• Thickness and production of sea ice in the Okhotsk Sea coastal polynyas from AMSR-E

  Sohey Nihashi, Kay I. Ohshima, Takeshi Tamura, Yasushi Fukamachi, Sei-Ichi Saitoh

  Journal of Geophysical Research: Oceans 114 10 2009年10月08日 [査読有り][通常論文]
   

  From comparisons with thickness of sea ice from Advanced Very High Resolution Radiometer (AVHRR) and ice-profiling sonar data we have developed an Advanced Microwave Scanning Radiometer-EOS (AMSR-E) thin ice thickness algorithm for the Sea of Okhotsk. This algorithm can estimate ice thickness of < 0.2 m without snow using the polarization ratio of AMSR-E brightness temperature at a 36.5 GHz channel from a linear relationship with AVHRR ice thickness. When a snow cover exists on the thin ice surface, as occurred a few times in each winter, it is shown that the algorithm cannot detect the thin ice. Sea ice and dense shelf water (DSW) production in coastal polynya are estimated on the basis of heat flux calculation with the daily AMSR-E ice thickness for three winters (December-March) of 2002-2003 to 2004-2005. The ice production is largest in the northwest shelf (NWS) polynya which accounts for ~45% of the sum of ice production in major coastal polynyas. The ice production in major coastal polynyas would cover the maximum ice area of the Okhotsk Sea if the average ice thickness is assumed to be 1 m. Variability of the ice production is mainly modulated by air temperature. In the NWS polynya, which is the main DSW production area, the annual DSW formation rate is estimated to be ∼0.36 Sv. Copyright 2009 by the American Geophysical Union.
• Thickness and production of sea ice in the Okhotsk Sea coastal polynyas from AMSR-E

  Sohey Nihashi, Kay I. Ohshima, Takeshi Tamura, Yasushi Fukamachi, Sei-ichi Saitoh

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 114 C10 C10025  2009年10月 [査読有り][通常論文]
   

  From comparisons with thickness of sea ice from Advanced Very High Resolution Radiometer (AVHRR) and ice-profiling sonar data we have developed an Advanced Microwave Scanning Radiometer-EOS (AMSR-E) thin ice thickness algorithm for the Sea of Okhotsk. This algorithm can estimate ice thickness of <= 0.2 m without snow using the polarization ratio of AMSR-E brightness temperature at a 36.5 GHz channel from a linear relationship with AVHRR ice thickness. When a snow cover exists on the thin ice surface, as occurred a few times in each winter, it is shown that the algorithm cannot detect the thin ice. Sea ice and dense shelf water (DSW) production in coastal polynya are estimated on the basis of heat flux calculation with the daily AMSR-E ice thickness for three winters (December-March) of 2002-2003 to 2004-2005. The ice production is largest in the northwest shelf (NWS) polynya which accounts for similar to 45% of the sum of ice production in major coastal polynyas. The ice production in major coastal polynyas would cover the maximum ice area of the Okhotsk Sea if the average ice thickness is assumed to be 1 m. Variability of the ice production is mainly modulated by air temperature. In the NWS polynya, which is the main DSW production area, the annual DSW formation rate is estimated to be similar to 0.36 Sv.
• HF radar technology in the Sea of Okhotsk

  Ebuchi, N, Y. Fukamachi, K.I. Ohshima, M. Wakatsuchi

  PICES Science Report 36 197 - 202 2009年09月 [査読有り][招待有り]
  
• Direct observations of sea-ice thickness and brine rejection off Sakhalin in the Sea of Okhotsk

  Yasushi Fukamachi, Kunio Shirasawa, Anatoliy M. Polomoshnov, Kay I. Ohshima, Ervin Kalinin, Sohey Nihashi, Humfrey Melling, Genta Mizuta, Masaaki Wakatsuchi

  CONTINENTAL SHELF RESEARCH 29 11-12 1541 - 1548 2009年06月 [査読有り][通常論文]
   

  From December to June 2002-2003, sea-ice and oceanic data were obtained from moorings near Sakhalin in the west central Okhotsk Sea. Ice draft measured by sonar reveals distinct periods of thin and thick ice. Thin-ice periods in January-March corresponded to offshore ice movement and increasing seawater salinity. The measured change in salinity corresponds well with that derived from heat-flux calculations using the observed ice thickness. Brine rejection from ice growing in a coastal polynya off northern Sakhalin is responsible for much of the observed salinity increase. The simultaneous observation of dense shelf water (> 26.7 sigma(0)) suggests that this region is one possible source. The periods of thick-ice incursion are likely indicative of heavily deformed pack formed further north and drifting south with the current. The mean draft (1.95 m), thick-ice ratio, and keel frequency during these periods are close to values observed in the Beaufort Sea. Freshwater transport estimated from the observed ice thickness and velocity is larger than that of the Amur River discharge. (C) 2009 Elsevier Ltd. All rights reserved.
• Subinertial and seasonal variations in the Soya Warm Current revealed by HF ocean radars, coastal tide gauges, and bottom-mounted ADCP

  Naoto Ebuchi, Yasushi Fukamachi, Kay I. Ohshima, Masaaki Wakatsuchi

  JOURNAL OF OCEANOGRAPHY 65 1 31 - 43 2009年02月 [査読有り][通常論文]
   

  Subinertial and seasonal variations in the Soya Warm Current (SWC) are investigated using data obtained by high frequency (HF) ocean radars, coastal tide gauges, and a bottom-mounted acoustic Doppler current profiler (ADCP). The HF radars clearly captured the seasonal variations in the surface current fields of the SWC. Almost the same seasonal cycle was repeated in the period from August 2003 to March 2007, although interannual variations were also discernible. In addition to the annual and interannual variations, the SWC exhibited subinertial variations with a period of 5-20 days. The surface transport by the SWC was significantly correlated with the sea level difference between the Sea of Japan and Sea of Okhotsk for both the seasonal and subinertial variations, indicating that the SWC is driven by the sea level difference between the two seas. The generation mechanism of the subinertial variation is discussed using wind data from the European Centre for Medium-range Weather Forecasts (ECMWF) analyses. The subinertial variations in the SWC were significantly correlated with the meridional wind stress component over the region. The subinertial variations in the sea level difference and surface current delay from the meridional wind stress variations by one or two days. Sea level difference through the strait caused by wind-generated coastally trapped waves (CTWs) along the east coast of Sakhalin and west coast of Hokkaido is considered to be a possible mechanism causing the subinertial variations in the SWC.
• Seasonal and subinertial variations in the Soya Warm Current revealed by HF radars, coastal tide gauges, and bottom-mounted ADCP.

  Ebuchi, N, Y. Fukamachi, K.I. Ohshima, M. Wakatsuchi

  Proceedings of ISRS 2008 TB202  2008年10月 [査読無し][通常論文]
  
• Deep western boundary current and southern frontal systems of the Antarctic Circumpolar Current southeast of the Kerguelen Plateau

  Shigeru Aoki, Nobuhiro Fujii, Shuki Ushio, Yasushi Yoshikawa, Shuichi Watanabe, Genta Mizuta, Yasushi Fukamachi, Masaaki Wakatsuchi

  Journal of Geophysical Research: Oceans 113 8 2008年08月08日 [査読有り][通常論文]
   

  The structure of the deep western boundary current and southern frontal systems of the Antarctic Circumpolar Current (ACC) southeast of the Kerguelen Plateau were investigated. Top-to-bottom hydrography was conducted around 58°S, and two underway observations were made around 56°S and 61°S. Middepth floats were also used to describe the subsurface flow and temperature fields. Along the 58°S section, a cold dome was located just off the plateau, and northwestward and southeastward flows were found in its western and eastern sides. The observed flow structure was highly barotropic. The maximum volume transport of the bottom water was 22 Sv equatorward, including a possible cyclonic recirculation of 10 Sv. The transport of the deep recirculation can be explained by the potential vorticity homogenization in the closed isopachs formed by the bottom slope off the plateau and the overlying ACC flowing southeastward through the Fawn Trough. The spatial scale of the cold dome, which showed a signature of the southern ACC front, was around 100 km at 58°S, and the similar cold domes were also found around 56°S and 61°S, along with a signature of the southern boundary of ACC around 61°S. The sharp excursion of the southern ACC front was also confirmed by the middepth float trajectories and the distribution of temperature maximum. This indicates the equatorward excursion up to 54°S, with the warmer ACC water just east of the southern frontal systems. Copyright 2008 by the American Geophysical Union.
• Deep western boundary current and southern frontal systems of the Antarctic Circumpolar Current southeast of the Kerguelen Plateau

  Shigeru Aoki, Nobuhiro Fujii, Shuki Ushio, Yasushi Yoshikawa, Shuichi Watanabe, Genta Mizuta, Yasushi Fukamachi, Masaaki Wakatsuchi

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 113 C8 2008年08月 [査読有り][通常論文]
   

  [1] The structures of the deep western boundary current and southern frontal systems of the Antarctic Circumpolar Current (ACC) southeast of the Kerguelen Plateau were investigated. Top-to-bottom hydrography was conducted around 58 degrees S, and two underway observations were made around 56 degrees S and 61 degrees S. Middepth floats were also used to describe the subsurface flow and temperature fields. Along the 58 degrees S section, a cold dome was located just off the plateau, and northwestward and southeastward flows were found in its western and eastern sides. The observed flow structure was highly barotropic. The maximum volume transport of the bottom water was 22 Sv equatorward, including a possible cyclonic recirculation of 10 Sv. The transport of the deep recirculation can be explained by the potential vorticity homogenization in the closed isopachs formed by the bottom slope off the plateau and the overlying ACC flowing southeastward through the Fawn Trough. The spatial scale of the cold dome, which showed a signature of the southern ACC front, was around 100 km at 58 degrees S, and the similar cold domes were also found around 56 degrees S and 61 degrees S, along with a signature of the southern boundary of ACC around 61 degrees S. The sharp excursion of the southern ACC front was also confirmed by the middepth float trajectories and the distribution of temperature maximum. This indicates the equatorward excursion up to 54 degrees S, with the warmer ACC water just east of the southern frontal systems.
• Volume transport of the Soya Warm Current revealed by bottom-mounted ADCP and ocean-radar measurement

  Yasushi Fukamachi, Iori Tanaka, Kay I. Ohshima, Naoto Ebuchi, Genta Mizuta, Hideo Yoshida, Shiro Takayanagi, Masaaki Wakatsuchi

  JOURNAL OF OCEANOGRAPHY 64 3 385 - 392 2008年06月 [査読有り][通常論文]
   

  The vertical structure of the Soya Warm Current (SWC) was observed by a bottom-mounted acoustic Doppler current profiler (ADCP) in the region of the SWC axis near the Soya Strait during a I-year period from May 2004. The ADCP data revealed a marked seasonal variability in the vertical structure, with positive (negative) vertical shear in summer and fall (winter and spring). The volume transport of the SWC is estimated on the basis of both the vertical structure observed by the ADCP and horizontal structure observed by the ocean radars near the strait. The transport estimates have a minimum in winter and a maximum in fall, with the yearly-averaged values in the range of 0.94-1.04 Sv (1 Sv = 10(6) m(3) s(-1)). These lie within a reasonable range in comparison to those through other straits in the Japan Sea.
• Diurnal coastal-trapped waves on the eastern shelf of Sakhalin in the Sea of Okhotsk and their modification by sea ice

  Jun Ono, Kay I. Ishima, Genta Mizuta, Yasushi Fukamachi, Masaaki Wakatsuchi

  CONTINENTAL SHELF RESEARCH 28 6 697 - 709 2008年04月 [査読有り][通常論文]
   

  From July 1998 to June 2000, the first long-term mooring measurements were carried out off the east coast of Sakhalin. Using these data, we examined the characteristies of the tidal heights and currents. The tidal heights and currents are dominated by the diurnal variability with fortnightly modulation over the northern part of the shelf. The K, and 01 tidal current ellipses are clockwise with their major axes along the isobaths and their signal propagates with the coast on the right with phase speeds of 3.4 and 3.8 m s(-1), respectively. The diurnal tidal Currents are almost uniform in the vertical direction except for the bottom Ekman layer. The thickness of the bottom Ekman layer caused by the diurnal tidal currents is larger in the region of stronger tidal currents, reaching 20-30 in over the northern part of the shelf. The diurnal tidal Currents over the northern part of the shelf can be explained by the first-mode diurnal coastal-trapped waves (CTWs). The diurnal CTWs are almost independent of the seasonal variability of density stratification and contribute significantly to diurnal currents, but only slightly to sea-surface heights. The diurnal tidal Currents over the southern part of the shelf are significantly smaller than those over the northern part. This is because the diurnal CTWs cannot exist south of similar to 52 degrees N from the dispersion relation. The diurnal tidal currents are significantly reduced over the northern shelf, where the diurnal CTWs exist, during the high sea-ice concentration periods. From this result, we propose the scenario that the CTWs are damped by the spin-down effect due to the Ekman layer that would occur underneath the sea ice. (C) 2007 Elsevier Ltd. All rights reserved.
• Vertical material flux under seasonal sea ice in the Okhotsk Sea north of Hokkaido, Japan

  Takehiko Hiwatari, Kunio Shirasawa, Yasushi Fukamachi, Ryuichi Nagata, Tomoyoshi Koizumi, Hiroshi Koshikawa, Kunio Kohata

  Polar Science 2 1 41 - 54 2008年03月 [査読有り][通常論文]
   

  Downward material fluxes under seasonal sea ice were measured using a time-series sediment trap installed at an offshore site in the Okhotsk Sea north of Hokkaido, Japan, from 13 January to 23 March 2005. The maximum fluxes of lithogenic material (753 mg m-2 day-1) and organic matter (mainly detritus 333 mg m-2 day-1) were recorded during the period in which sea ice drifted ashore and increased in extent, from 13 January to 9 February. Organic matter as fecal pellets (81-93 mg m-2 day-1) and opal as biosilica (51-67 mg m-2 day-1), representing diatom fluxes, were abundant in sediment trap samples obtained during the period of full sea ice coverage from 10 February to 9 March. Microscopic observations revealed that fecal pellets were largely diatom frustules, suggesting that zooplankton actively grazed on ice algae during the period of full sea ice coverage. During the period of retreating sea ice, from 10 to 23 March, the phytoplankton flux showed a rapid increase (from 9.5 to 22.5 × 106 cells m-2 day-1), reflecting their release into the water column as the sea ice melted. Our results demonstrate that the quantity and quality of sinking biogenic and lithogenic materials vary with the seasonal extent of sea ice in mid-winter. © 2008 Elsevier B.V. and NIPR.
• Deep western boundary current and southern frontal systems of the Antarctic Circumpolar Current southeast of the Kerguelen Plateau

  Aoki, S, N. Fujii, S. Ushio, Y. Yoshikawa, S. Watanabe, G. Mizuta, Y. Fukamachi, M. Wakatsuchi

  Journal of Geophysical Research 113 C8 C08038  2008年 [査読有り][通常論文]
  
• Variations in the Soya Warm Current observed by HF ocean radar, coastal tide gauges and satellite altimetry.

  Ebuchi, N, Y. Fukamachi, K.I. Ohshima, K. Shirasawa, M. Wakatsuchi

  Proceedings of ISRS2008PORSEC (CD-ROM) TA1001  2006年11月 [査読無し][通常論文]
  
• Sea ice thickness in the southwestern Sea of Okhotsk revealed by a moored ice-profiling sonar

  Yasushi Fukamachi, Genta Mizuta, Kay I. Ohshima, Takenobu Toyota, Noriaki Kimura, Masaaki Wakatsuchi

  Journal of Geophysical Research: Oceans 111 9 2006年09月08日 [査読有り][通常論文]
   

  Using a moored ice-profiling sonar along with a moored acoustic Doppler current profiler, a total spatial section of draft across 3334 km of sea ice was obtained in the southwestern Sea of Okhotsk near Hokkaido in the winters of 1999-2001. Using this draft data set, the average draft and keel statistics are discussed in this sea for the first time. The mean draft was 0.60 m, which corresponds to the thickness of 0.71 m, over the three winters with the range of 0.49-0.72 m for each winter. The classification of level and deformed ice reveals a small range of the monthly mean level ice draft (0.18-0.27 m) and the dominance of the deformed ice in terms of volume (80%). The mean draft varied with the areal ratio of the deformed ice fairly well. These results suggest that dynamic processes such as ridging and rafting are important for the evolution of draft in the region of observation. The observed draft probability density distribution and keel statistics show that the thick ice ratio and keel frequency are lower than the similar data in polar regions and closer to those observed in Davis Strait west of Greenland. Along with the ice concentration and speed derived from the satellite data the southward ice transport to the southwestern Sea of Okhotsk is estimated on the basis of the observed sea ice thickness. The estimated ice transport ranged from 15 to 70 km3 in each winter. The heat and freshwater transport associated with the ice transport ranged from -3.9 × 1017 to -1.8 × 1018 J and from 12 to 57 km3, respectively. Copyright 2006 by the American Geophysical Union.
• Sea ice thickness in the southwestern Sea of Okhotsk revealed by a moored ice-profiling sonar

  Yasushi Fukamachi, Genta Mizuta, Kay I. Ohshima, Takenobu Toyota, Noriaki Kimura, Masaaki Wakatsuchi

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 111 C9 doi:10.1029/2005JC003327  2006年09月 [査読有り][通常論文]
   

  [ 1] Using a moored ice-profiling sonar along with a moored acoustic Doppler current profiler, a total spatial section of draft across 3334 km of sea ice was obtained in the southwestern Sea of Okhotsk near Hokkaido in the winters of 1999 - 2001. Using this draft data set, the average draft and keel statistics are discussed in this sea for the first time. The mean draft was 0.60 m, which corresponds to the thickness of 0.71 m, over the three winters with the range of 0.49 - 0.72 m for each winter. The classification of level and deformed ice reveals a small range of the monthly mean level ice draft (0.18 - 0.27 m) and the dominance of the deformed ice in terms of volume (80%). The mean draft varied with the areal ratio of the deformed ice fairly well. These results suggest that dynamic processes such as ridging and rafting are important for the evolution of draft in the region of observation. The observed draft probability density distribution and keel statistics show that the thick ice ratio and keel frequency are lower than the similar data in polar regions and closer to those observed in Davis Strait west of Greenland. Along with the ice concentration and speed derived from the satellite data the southward ice transport to the southwestern Sea of Okhotsk is estimated on the basis of the observed sea ice thickness. The estimated ice transport ranged from 15 to 70 km 3 in each winter. The heat and freshwater transport associated with the ice transport ranged from - 3.9 x 10(17) to - 1.8 x 10(18) J and from 12 to 57 km(3), respectively.
• Observation of the Soya Warm Current combining HF ocean radar with coastal tide gauges and satellite altimetry.

  Ebuchi, N, Y. Fukamachi, K.I. Ohshima, K. Shirasawa, M. Wakatsuchi

  Proceedings of IGARSS 2006 1860 - 1863 2006年07月 [査読無し][通常論文]
  
• Amplification of diurnal tides over Kashevarov Bank in the Sea of Okhotsk and its impact on water mixing and sea ice

  J Ono, KI Ohshima, G Mizuta, Y Fukamachi, M Wakatsuchi

  DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 53 3 409 - 424 2006年03月 [査読有り][通常論文]
   

  To clarify the characteristics of tidal currents and heights over Kashevarov Bank (KB) in the Sea of Okhotsk, continuous mooring observation with ADCP and CT sensors was carried out near the summit of KB from 20 September 1999 to 20 June 2000. The velocity, sea-surface height, and bottom-water temperature were dominated by the diurnal signal with fortnightly modulation. The velocity amplitude reached similar to 1.4 in s(-1) during the spring tide. The K-1 and O-1 tidal current ellipses are clockwise with a nearly circular shape and nearly barotropic. To interpret the physical mechanism of the amplified diurnal currents over KB, a seamount-trapped wave (SMTW) model was applied to KB. The frequency of SMTW approximated to KB is close to the diurnal tidal frequencies for the first-gravest mode of first azimuthal wavenumber. The structure and properties of the SMTW mode are consistent with the observations. It is proposed that the amplified diurnal currents over KB are caused by the resonance with SMTW. The observed fortnightly variability in tidal currents and bottom- and surface-temperatures suggests that both the cold spot in summer and the low sea-ice concentration in winter over KB are due to the horizontal and vertical mixing with the surrounding subsurface water, caused by strong tidal currents. (c) 2005 Elsevier Ltd. All rights reserved.
• Observation of the Soya Warm Current using HF ocean radar

  N Ebuchi, Y Fukamachi, KI Ohshima, K Shirasawa, M Ishikawa, T Takatsuka, T Daibo, M Wakatsuchi

  JOURNAL OF OCEANOGRAPHY 62 1 47 - 61 2006年02月 [査読有り][通常論文]
   

  Three High Frequency (HF) ocean radar stations were installed around the Soya/La Perouse Strait in the Sea of Okhotsk in order to monitor the Soya Warm Current (SWC). The frequency of the HF radar is 13.9 MHz, and the range and azimuth resolutions are 3 km and 5 deg., respectively. The radar covers a range of approximately 70 km from the coast. The surface current velocity observed by the HF radars was compared with data from drifting buoys and shipboard Acoustic Doppler Current Profilers (ADCPs). The current velocity derived from the HF radars shows good agreement with that observed using the drifting buoys. The root-mean-square (rms) differences were found to be less than 20 cm s(-1) for the zonal and meridional components in the buoy comparison. The observed current velocity was also found to exhibit reasonable agreement with the shipboard ADCP data. It was shown that the HF radars clearly capture seasonal and short-term variations of the SWC. The velocity of the Soya Warm Current reaches its maximum, approximately 1 m s(-1), in summer and weakens in winter. The velocity core is located 20 to 30 km from the coast, and its width is approximately 40 km. The surface transport by the SWC shows a significant correlation with the sea level difference along the strait, as derived from coastal tide gauge records at Wakkanai and Abashiri.
• The variability of the East Sakhalin Current induced by winds over the continental shelf and slope

  G Mizuta, KI Ohshima, Y Fukamachi, M Wakatsuchi

  JOURNAL OF MARINE RESEARCH 63 6 1017 - 1039 2005年11月 [査読有り][通常論文]
   

  Long-term current measurements of the East Sakhalin Current (ESC) in the Sea of Okhotsk are analyzed using the technique of empirical orthogonal functions (EOFs) in the frequency domain. The first and second EOFs at subtidal frequencies represent motions over the continental shelf and slope, respectively, corresponding to the variability of the two cores of the intense ESC. The first EOF can be explained by the first-mode coastal trapped wave (CTW). The structure of the second EOF is similar to that of the second-mode CTW to the first approximation. According to the distribution of the cross-spectra between EOFs and the wind stress over the whole area of the Sea of Okhotsk, the first EOF is correlated with the alongshore component of the wind stress over the northern and western shelves. The distribution of the phase of the wind stress, which is correlated with the first EOF, indicates that a resonance between the CTW and wind stress drives the motion represented by the first EOF at lower frequencies. At higher frequencies the phase of the wind stress correlated with the first EOF is almost uniform in space, being consistent with the greater speed of phase propagation of the EOF compared with that for the free CTW at these frequencies. The second EOF is correlated with the wind stress curl in the central part of the Sea of Okhotsk. The motion by the second EOF is confined over the slope at lower frequencies and becomes large over the shelf at higher frequencies. This change in the structure of the second EOF is consistent with the results of the numerical experiment of the flow induced by the offshore forcing by Chapman and Brink (1987). The phase of the wind stress curl which is correlated with the second EOF changes clearly in space at some frequencies, suggesting that the motion represented by the second EOF propagates along the isobath with the coast to the fight. The wind stress curl contains the wavenumber resonant with the lowest two or three modes of CTWs.
• A generation mechanism for mesoscale eddies in the Kuril Basin of the Okhotsk Sea: Baroclinic instability caused by enhanced tidal mixing

  KI Ohshima, Y Fukamachi, T Mutoh, M Wakatsuchi

  JOURNAL OF OCEANOGRAPHY 61 2 247 - 260 2005年04月 [査読有り][通常論文]
   

  Mesoscale eddies, particularly anticyclonic ones, are dominant features in the Kuril Basin of the Okhotsk Sea. In 1999, both surface drifter and hydrographic observations caught the same anticyclonic eddy northwest of Bussol' Strait, which has a diameter of similar to100 km, typical surface velocity of 0.2-0.3 m s(-1), and less dense core extending to a depth of similar to1200 m. Based on an idea that the generation of mesoscale eddies is caused by strong tidal mixing in and around Kuril Straits, we have conducted a series of three-dimensional numerical model experiments, in which strong tidal mixing is simply parameterized by increasing coefficients of vertical eddy viscosity and diffusivity along the eastern boundary. Initially, a regular series of disturbances with a wavelength of similar to70 km starts to develop. The disturbances can be clearly explained by a linear instability theory and regarded as the baroclinic instability associated with the near-surface front formed in the region between the enhanced mixing and offshore regions. In the mature phase, the disturbances grow large enough that some eddies pinch off and advect offshore (westward), with the scale of disturbances increasing gradually. Typical eddy scale and its westward propagation speed are similar to100 krn and similar to0.6 km day(-1), respectively, which are consistent with the observations by satellites. The westward propagation can be explained partly due to nonlinear effect of self-offshore advection and partly due to the beta-effect. With the inclusion of the upper ocean restoring, the dominance of anticyclonic eddy, extending from surface to a depth of similar to1200 m, can be reproduced.
• Seasonal variation of the Soya Warm Current observed by HF ocean radar.

  Ebuchi, N, Y. Fukamachi, K.I. Ohshima, K. Shirasawa, M. Ishikawa, T. Takatsuka, T. Daibo, M. Wakatsuchi

  Proceedings of ISRS 2004 183 - 187 2004年10月 [査読無し][通常論文]
  
• Transport and modification processes of dense shelf water revealed by long-term moorings off Sakhalin in the Sea of Okhotsk

  Yasushi Fukamachi, Genta Mizuta, Kay I. Ohshima, Lynne D. Talley, Stephen C. Riser, Masaaki Wakatsuchi

  Journal of Geophysical Research C: Oceans 109 9 1 - 16 2004年09月15日 [査読有り][通常論文]
   

  The region off the east coast of Sakhalin is thought of as an important pathway of dense shelf water (DSW) from its production region in the northwestern Okhotsk Sea to the southern Okhotsk Sea. From July 1998 to June 2000, the first long-term mooring experiment was carried out in this region to observe the southward flowing East Sakhalin Current (ESC) and DSW. Moored and associated hydrographic data show considerable modification of cold dense water via mixing with warm offshore water in the slope region off northern Sakhalin. Significant onshore eddy heat flux was observed at the northernmost mooring (54.9°N), which suggests the occurrence of baroclinic instability. The eddy heat flux was not significant farther south. At moorings along 53°N, cold anticyclonic eddies were identified that were consistent with isolated eddies seen in the hydrographic data. The three years of hydrographic data also showed large differences in extent and properties of DSW. Furthermore, the mooring data show that seasonal variability of DSW was quite different in the two years. The average DSW transport for σ θ > 26.7 evaluated using the moored data at 53°N for 1 year (1998-1999) was ∼0.21 Sv (= 106 m3 s-1). This value is at the lower end of the previous indirect estimates. Along with the DSW modification, this transport estimate indicates that DSW was not only carried southward by the ESC but was spread offshore by eddies off northern Sakhalin. Copyright 2004 by the American Geophysical Union.
• Biogenic and lithogenic particle fluxes in the western region of the Sea of Okhotsk: Implications for lateral material transport and biological productivity

  Takeshi Nakatsuka, Tomoaki Fujimune, Chisato Yoshikawa, Shinichiro Noriki, Kimitaka Kawamura, Yasushi Fukamachi, Genta Mizuta, Masaaki Wakatsuchi

  Journal of Geophysical Research C: Oceans 109 9 1 - 15 2004年09月15日 [査読有り][通常論文]
   

  Sinking particles collected at two depths at two sites off Sakhalin Island in the western region of the Sea of Okhotsk were analyzed to determine their major chemical components (lithogenic material, biogenic opal, calcium carbonate (CaCO3), and total organic carbon (TOC)). The lithogenic and opal fluxes increased downward, indicating the lateral input of resuspended sedimentary particles into the lower traps, while the CaCO3 or TOC fluxes did not change greatly between the upper and lower traps. The lithogenic particle flux in the lower traps showed intermittent increase events frequently during periods when cold water masses penetrated into the intermediate layer at the mooring sites. This coincidence between the flux increase and the cooling of the intermediate layer clearly indicates that the cold and turbid Dense Shelf Water (DSW) is discharged from the bottom of the northwestern continental shelf to the pelagic intermediate layer, supplying large amounts of particulate matter onto the bottom of the slope and deep basin. After removing the effect of the lateral input, the time series of the opal export from the surface water at the mooring sites were reconstructed using the upper trap data. There were two predominant characteristics in the seasonal variations of the opal export, which is nearly equal to the diatom production, in the area off Sakhalin. One is the relatively large opal flux in autumn, and the other is the southward propagation of the spring diatom bloom, although the sea ice retreats northward every spring. Both of these characteristics suggest that the river water discharged from the Amur, together with the seasonal sea ice cover, regulates primary production in this area. Copyright 2004 by the American Geophysical Union.
• Observation of the Soya Warm Current using HF ocean radar.

  Ebuchi, N, Y. Fukamachi, K.I. Ohshima, K. Shirasawa, M. Ishikawa, T. Takatsuka, T. Daibo, M. Wakatsuchi

  Proceedings of IGARSS 2004 1175 - 1178 2004年09月 [査読無し][通常論文]
  
• Biogenic and lithogenic particle fluxes in the western region of the Sea of Okhotsk: Implications for lateral material transport and biological productivity

  T Nakatsuka, T Fujimune, C Yoshikawa, S Noriki, K Kawamura, Y Fukamachi, G Mizuta, M Wakatsuchi

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 109 C9 doi:10.1029/2003JC001908  2004年08月 [査読有り][通常論文]
   

  Sinking particles collected at two depths at two sites off Sakhalin Island in the western region of the Sea of Okhotsk were analyzed to determine their major chemical components (lithogenic material, biogenic opal, calcium carbonate (CaCO3), and total organic carbon (TOC)). The lithogenic and opal fluxes increased downward, indicating the lateral input of resuspended sedimentary particles into the lower traps, while the CaCO3 or TOC fluxes did not change greatly between the upper and lower traps. The lithogenic particle flux in the lower traps showed intermittent increase events frequently during periods when cold water masses penetrated into the intermediate layer at the mooring sites. This coincidence between the flux increase and the cooling of the intermediate layer clearly indicates that the cold and turbid Dense Shelf Water (DSW) is discharged from the bottom of the northwestern continental shelf to the pelagic intermediate layer, supplying large amounts of particulate matter onto the bottom of the slope and deep basin. After removing the effect of the lateral input, the time series of the opal export from the surface water at the mooring sites were reconstructed using the upper trap data. There were two predominant characteristics in the seasonal variations of the opal export, which is nearly equal to the diatom production, in the area off Sakhalin. One is the relatively large opal flux in autumn, and the other is the southward propagation of the spring diatom bloom, although the sea ice retreats northward every spring. Both of these characteristics suggest that the river water discharged from the Amur, together with the seasonal sea ice cover, regulates primary production in this area.
• Transport and modification processes of dense shelf water revealed by long-term moorings off Sakhalin in the Sea of Okhotsk

  Y Fukamachi, G Mizuta, KI Ohshima, LD Talley, SC Riser, M Wakatsuchi

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 109 C9 doi:10.1029/2003JC001906  2004年07月 [査読有り][通常論文]
   

  The region off the east coast of Sakhalin is thought of as an important pathway of dense shelf water (DSW) from its production region in the northwestern Okhotsk Sea to the southern Okhotsk Sea. From July 1998 to June 2000, the first long-term mooring experiment was carried out in this region to observe the southward flowing East Sakhalin Current (ESC) and DSW. Moored and associated hydrographic data show considerable modification of cold dense water via mixing with warm offshore water in the slope region off northern Sakhalin. Significant onshore eddy heat flux was observed at the northernmost mooring (54.9degreesN), which suggests the occurrence of baroclinic instability. The eddy heat flux was not significant farther south. At moorings along 53degreesN, cold anticyclonic eddies were identified that were consistent with isolated eddies seen in the hydrographic data. The three years of hydrographic data also showed large differences in extent and properties of DSW. Furthermore, the mooring data show that seasonal variability of DSW was quite different in the two years. The average DSW transport for sigma(theta) > 26.7 evaluated using the moored data at 53degreesN for 1 year (1998-1999) was similar to0.21 Sv (= 10(6) m(3) s(-1)). This value is at the lower end of the previous indirect estimates. Along with the DSW modification, this transport estimate indicates that DSW was not only carried southward by the ESC but was spread offshore by eddies off northern Sakhalin.
• Winter mixed layer and its yearly variability under sea ice in the southwestern part of the Sea of Okhotsk

  G Mizuta, KI Ohshima, Y Fukamachi, M Itoh, M Wakatsuchi

  CONTINENTAL SHELF RESEARCH 24 6 643 - 657 2004年04月 [査読無し][通常論文]
   

  Hydrographic observations under sea ice were conducted in the southwestern part of the Sea of Okhotsk for 4 years from 1996 to 1999. Every year a cold mixed layer with near-freezing temperature was distributed from the sea surface to a depth of 150-300 m near the shelf break under sea ice. The thicknesses of the mixed layer and sea ice were largest in 1997. While the depth of the mixed layer was considerably deeper than that of dichothermal water, which is identified as a temperature minimum from spring to fall in this region, the density of water in the mixed layer was equal to or less than that of dichothermal water. It is shown that deepening of isopycnals due to the alongshore component of the wind stress is essential for thickening of the mixed layer. In 1997 the nearly northerly winds, which are usually directed offshore, were more parallel to the coast than those in the other years. Thickening of the mixed layer in 1997 is attributed to this wind condition. The air temperature and wind indicate that the sea-ice production rate was low in 1997, whereas the wind direction was favorable for rafting and ridging. Thus the change in wind direction is proposed As an important factor in determining the thickness of both the mixed layer and the sea ice in this region. (C) 2004 Elsevier Ltd. All rights reserved.
• Sverdrup balance and the cyclonic gyre in the Sea of Okhotsk

  KI Ohshima, D Simizu, M Itoh, G Mizuta, Y Fukamachi, SC Riser, M Wakatsuchi

  JOURNAL OF PHYSICAL OCEANOGRAPHY 34 2 513 - 525 2004年02月 [査読有り][通常論文]
   

  It is proposed that the cyclonic gyre over the northern half-basin of the Okhotsk Sea is driven by the wind stress curl and that a major part of the East Sakhalin Current (ESC) can be regarded as its western boundary current. Both from the high-resolution ECMWF and Comprehensive Ocean-Atmosphere Dataset (COADS) data, the annual mean wind stress curl is positive over the sea. When the Sverdrup streamfunction is calculated by excluding the shallow shelves, the streamfunction shows a cyclonic pattern over the central basin, which is roughly consistent with the geopotential anomaly distribution from all the available hydrographic data. Profiling floats suggest that the cyclonic gyre extends to at least a depth of 500 m: a relatively intense southward flow (ESC) with an average speed of approximately 10 cm s(-1) near the western boundary and slow northward flow with an average speed of approximately 2 cm s(-1) in the east. Climatological data show that along zonal sections at 50degrees-53degreesN isopycnal surfaces gradually rise from the east to west and sharply drop near the western boundary, suggesting the Sverdrup balance. This feature persists throughout the year. The integrated northward baroclinic transport of 3.5 Sv along 53degreesN is comparable to the Sverdrup transport of 3.7 Sv, calculated from the annual mean wind stress. Sverdrup balance appears to hold roughly in the baroclinic field in 50degrees-53degreesN. A flat-bottom numerical model forced by realistic wind stress reproduces well the cyclonic gyre, with the observed baroclinic features. In the south, the anticyclonic circulation in the Kuril Basin cannot be explained by the wind stress curl inside the Okhotsk Sea in this simplified model.
• Structure and seasonal variability of the East Sakhalin Current

  G Mizuta, Y Fukamachi, KI Ohshima, M Wakatsuchi

  JOURNAL OF PHYSICAL OCEANOGRAPHY 33 11 2430 - 2445 2003年11月 [査読有り][通常論文]
   

  In order to clarify the structure and seasonal variability of the flow field near the western boundary of the Sea of Okhotsk, long-term mooring measurements were carried out from 1998 to 2000 in this region. In most of the mooring period a persistent southward flow (the East Sakhalin Current) was observed, which extends from the surface to a depth around 1000 m. The speed of this southward flow clearly changed seasonally. The peak monthly mean speed along 53degreesN at a depth of 200 m attained a maximum of 37 6 9 cm s(-1) in January and a minimum of 10 +/- 8 cm s(-1) in July. Three different cores of intense flow were identified in the southward flow. The first core was centered over the continental slope and had rather large vertical extent, reaching the bottom on the slope. The second core was trapped over the shelf near the surface and was observed from October to November. This core was associated with less saline surface water affected by the Amur River discharge. The third core was intensified toward the bottom on the slope. The spatial and temporal distribution of this bottom-intensified core coincided with that of dense shelf water, which is formed over the broad shelf in the north. The intensity of this core damped within a few hundred kilometers from the northern end of Sakhalin probably because of strong mixing of dense shelf water with surrounding waters. The total transport of the southward flow at 53degreesN was 6.7 x 10(6) m(3) s(-1) in the annual average, varying from a maximum of 12.3 x 10(6) m(3) s(-1) in February and a minimum of 1.2 x 10(6) m(3) s(-1) in October. Most of the transport was maintained by the first core of the southward flow.
• Variability of sea-ice draft off Hokkaido in the Sea of Okhotsk revealed by a moored ice-profiling sonar in winter of 1999

  Y Fukamachi, G Mizuta, KI Ohshima, H Melling, D Fissel, M Wakatsuchi

  GEOPHYSICAL RESEARCH LETTERS 30 7 doi:10.1029/2002GL016197  2003年04月 [査読有り][通常論文]
   

  [1] Using a moored ice-profiling sonar along with an ADCP, a spatial section of draft across 855 km of sea ice was obtained for the first time in the southwestern part of the Okhotsk Sea near Hokkaido in winter of 1999. The draft evolved from 0.20 m in mid-February to 1.45 m in late March with the overall value of 0.72 m. The draft characteristics were quite different between February and March before and after the period of strong winds. The increase of the mean draft from February to March was associated with the increase of deformed ice. The maximum draft observed was similar to17 m. Ice volume was dominated by the contribution from portions of deformed ice especially in March. These results suggest that deformed ice dominated in the region of observation and dynamical processes were mainly responsible for the evolution of draft.
• Near-surface circulation and tidal currents of the Okhotsk Sea observed with satellite-tracked drifters

  KI Ohshima, M Wakatsuchi, Y Fukamachi, G Mizuta

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 107 C11 doi:10/1029/2001JC001005  2002年11月 [査読有り][通常論文]
   

  [1] Near-surface circulation of the Okhotsk Sea was observed with ARGOS drifters from August 1999 to February 2000. The drifters clearly revealed the existence of the southward boundary current (the East Sakhalin Current) off the east Sakhalin. This current is strongly controlled by bottom topography and confined to the region shallower than 1000 m. The volume transport of this current is estimated to be in the range of 4-9 Sv (1 Sv = 10(6) m(3) s(-1)), with the increase from summer to winter. The current appears to consist of two cores: one exists near the coast (50-150 m depths) with typical speeds of 0.3-0.4 m s(-1) and the other exists over the shelf slope (300-900 m depths) with typical speeds of 0.2-0.3 m s(-1). A part of this southward current continues as far as the southern tip of Sakhalin Island, while another part turns to the east around Terpeniya Bay (similar to48degreesN) flowing eastward as far as Bussol' Strait. Most of the drifters that survived in the Okhotsk Sea went out to the Pacific through Bussol' Strait by less than a half year, suggesting that Bussol' Strait is the main pathway for the surface water to flow out from the Okhotsk Sea. Mesoscale anticyclonic eddies with diameters of 100-200 km are dominant in the Kuril Basin. Diurnal shelf waves were identified over the shelf in the northern part of the east Sakhalin shelf. Large amplification of diurnal tidal currents (order of 1.0 m s(-1)) was observed over Kashevarov Bank along with the residual anticyclonic circulation. Both diurnal and semidiurnal tidal currents were found to be enhanced in and around Bussol' Strait.
• Deriving sea-ice thickness and ice types in the Sea of Okhotsk using dual-frequency airborne SAR (Pi-SAR) data

  T Matsuoka, S Uratsuka, M Satake, A Nadai, T Umehara, H Maeno, H Wakabayashi, F Nishio, Y Fukamachi

  ANNALS OF GLACIOLOGY, VOL 34, 2002 34 429 - 434 2002年 [査読有り][通常論文]
   

  Dual-frequency, multi-polarization airborne synthetic aperture radar (Pi-SAR; developed by the Communications Research Laboratory and National Space Development Agency of Japan) observations of the seasonal sea-ice region off Okhotsk coast of Hokkaido Japan, were carried out in February 1999 using X- and L-band radar frequencies with a resolution of 1.5 and 3.0 in. In conjunction with the SAR observations, the sea-ice thickness (draft) and velocity were Measured by a moored Ice Profiling Sonar (IPS) and an Acoustic Doppler Current Profiler (ADCP). Tracks of the sea Ice passing over the IPS were estimated front the time series of the ADCP ice-velocity and -direction data. Along these tracks, the SAR backscattering coefficient profiles were compared with the IPS ice-draft profiles. The results showed that the L-band SAR backscattering profiles correlated well with the IPS ice-draft data, particularly in the thicker part (a few meters thick) of the rim of first-year ice, which had a large backscattering coefficient. Although the X-band SAR backscattering profiles did not correlate well with the IPS data, thin ice (<10 cm thick) showed a large backscattering coefficient. The L-band SAR and IPS data did not distinguish thin ice front open water.
• Winter oceanographic conditions in the southwestern part of the Okhotsk sea and their relation to sea ice

  Kay I. Ohshima, Genta Mizuta, Motoyo Itoh, Yasushi Fukamachi, Tatsuro Watanabe, Yasushi Nabae, Koukichi Suehiro, Masaaki Wakatsuchi

  Journal of Oceanography 57 4 451 - 460 2001年 [査読有り][通常論文]
   

  In the southwestern part of the Okhotsk Sea, oceanographic and sea-ice observations on board the icebreaker Soya were carried out in February 1997. A mixed layer of uniform temperature nearly at the freezing point extending down to a depth of about 300 m was observed. This is much deeper than has previously been reported. It is suggested that this deep mixed layer originated from the north (off East Sakhalin), being advected along the shelf slope via the East Sakhalin Current, accompanied with the thick first-year ice (average thickness 0.6 m). This vertically uniform winter water, through mixing with the surrounding water, makes the surface water more saline (losing a characteristic of East Sakhalin Current Water) and the water in the 100-300 m depth zone less saline, colder, and richer in oxygen (a characteristic of the intermediate Okhotsk Sea water). The oceanographic structure and a heat budget analysis suggest that new ice zone, which often appears at ice edges, can be formed through preconditioning of thick ice advection and subsequent cooling by the latent heat release due to its melting.
• Seasonal variability of bottom water properties off Adelie Land, Antarctica

  Y Fukamachi, M Wakatsuchi, K Taira, S Kitagawa, S Ushio, A Takahashi, K Oikawa, T Furukawa, H Yoritaka, M Fukuchi, T Yamanouchi

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 105 C3 6531 - 6540 2000年03月 [査読有り][通常論文]
   

  The region off Adelie Land is considered as one of the sources of Antarctic Bottom Water. Hydrographic observations were carried out during two cruises in December 1994 and January 1995 and January and February 1996 in this region. Vertical sections along 140 degrees E show that bottom water is colder and fresher than the water above. This bottom water also has higher dissolved oxygen and lower silicate concentrations. The saline bottom water that originated from Ross Sea is not found in these hydrographic data obtained west of 142 degrees E. Current meter moorings were also carried out at three locations on the continental slope in this region, At one of these moorings (139 degrees 59'E, 65 degrees 10'S: 2665 m deep), data were successfully obtained from January 1995 to March 1996. Three current meters were deployed at 1075, 1778, and 2632 m deep in this mooring. The data show that the average current speed at the lower current meter is 16.2 cm s(-1); and it is about 3 times larger than those at the upper two current meters. Also, variability of speed and temperature is largest at the lower current meter. In addition, seasonal variability of speed and temperature is evident only at this current meter. From August to December? speed is larger by 5.7 cm s(-1) and temperature is lower by 0.27 degrees C. Also, their variability is larger during the same period. This seasonal variability observed near the bottom suggests seasonal variability of bottom water formation in this region.
• Mesoscale ice features in the summer marginal ice zone off East Queen Maud Land observed in NOAA AVHRR imagery

  Fukamachi, Y, K. I. Ohshima, T. Ishikawa

  Antarctic Research Series 74 317 - 324 1998年 [査読有り][通常論文]
  
• INSTABILITY OF DENSITY FRONTS IN LAYER AND CONTINUOUSLY STRATIFIED MODELS

  Y FUKAMACHI, JP MCCREARY, JA PROEHL

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 100 C2 2559 - 2577 1995年02月 [査読有り][通常論文]
   

  The instability of density fronts is investigated as a possible generation mechanism for the small-scale, wavelike patterns that are commonly observed along upwelling fronts and filaments. Unstable-wave solutions are obtained in two linearized models: a 1 1/2-layer model, and a continuously stratified model confined to the surface region of the ocean. In both systems the thickness of the upper region is held constant for the background state, the front being specified by allowing the temperature field T within the region to vary zonally. The background state in the layer model consists of vertically oriented isotherms associated with a depth-independent current, whereas in the continuously stratified model it consists of steeply tilted isotherms and a vertically sheared current. Solutions are found both when the background velocity field V is zonally uniform and when it is zonally sheared. When V is weak and zonally uniform, approximate solutions are derived analytically for both models that are valid for low-frequency, low-wavenumber waves. These solutions demonstrate that the unstable waves in the two systems are dynamically related, both being representations of ageostrophic baroclinic instability. Numerical solutions corroborate the analytic results and extend their range of validity. Energetics analyses confirm that the energy source for the waves is the background potential energy associated with the zonally varying T field. When V is a zonally sheared jet, the models still exhibit a band of instability, which is identifiable with ageostrophic baroclinic instability. The most unstable wave in this band has a short wavelength, a frequency near f/2, and a rapid growth rate consistent with observed features. The layer model also has a band of larger-scale waves that is a mixed, baroclinic-barotropic instability; however, for a typical frontal structure this band is weaker than the baroclinic band.
• A NONLINEAR MECHANISM FOR MAINTAINING COASTALLY TRAPPED EASTERN BOUNDARY CURRENTS

  JP MCCREARY, Y FUKAMACHI, P LU

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 97 C4 5677 - 5692 1992年04月 [査読有り][通常論文]
   

  Several versions of a 2 1/2-layer model are used to investigate a nonlinear mechanism for maintaining wind-driven currents trapped to an eastern ocean boundary. All the models neglect the advection terms in the momentum equations, retaining advection only in the continuity equations. Solutions are forced by a band of upwelling-favorable wind without curl. A possible solution to this system is a state of rest in which the upper layer pressure gradient everywhere balances the wind stress (the Sverdrup balance). As expected, solutions to a linearized version of the model adjust to this equilibrium state by the westward radiation of both mode-1 and mode-2 Rossby waves. In contrast, when the wind is sufficiently strong, the nonlinear solutions retain a reasonable coastal circulation (with an equatorward surface jet and a poleward undercurrent) even after 40 years of integration. The basic nonlinear process that causes this marked difference in response is the following: an onshore geostrophic flow, which compensates for offshore Ekman drift, is established by the radiation of mode-1 Rossby waves. and this current can be strong enough to reverse the propagation direction of mode-2 Rossby waves. As a consequence, the resulting eastern boundary currents are dynamically similar to the frictional, western boundary currents that occur in other models. The equilibrium state of the nonlinear solutions is presumably also a state of rest, but the diffusive adjustment occurs at such a slow rate that we have not been able to confirm this conclusion numerically.
• A NUMERICAL INVESTIGATION OF JETS AND EDDIES NEAR AN EASTERN OCEAN BOUNDARY

  JP MCCREARY, Y FUKAMACHI, PK KUNDU

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 96 C2 2515 - 2534 1991年02月 [査読有り][通常論文]
   

  The dynamics of the circulation near an eastern-ocean boundary are investigated using a 2 1/2-layer numerical model that includes entrainment of cool water into the upper layer. Solutions are found in a regional ocean basin and are forced by an upwelling-favorable, alongshore wind field without curl. Dynamically simpler versions of the model are also utilized in order to isolate the effects of various physical processes; in particular, a lineaized instability model is used to study the unstable waves associated with various background coastal circulations. The model is quite successful in simulating many features of the observed flow and SST fields. Initially, the "main run" solution spins up as in a linear model, generating a surface jet, an undercurrent, and an upwelling front. Subsequently, small-scale, "fingerlike" disturbances appear along the coast and grow rapidly in amplitude and scale. The growth in scale has two causes: the slower development of larger-scale disturbances, and eddy coalescence via nonlinear interactions. Eventually, the solution adjusts to a realistic equilibrium state that contains upwelling filaments, squirts, eddies, dipole eddy pairs, and a realistic mean circulation. Entrainment is a crucial process in the dynamics of the mean flow. In particular, entrainment damps the westward propagation of Rossby waves, thereby ensuring that the currents remain coastally trapped. (In this aspect entrainment plays a dynamical role similar to vertical mixing in continuously stratified models.) Eddies influence the mean flow primarily by providing a strong heat source near the coast, but they have very little effect on the mean momentum field. The small-scale, fingerlike disturbances are caused by a frontal instability that requires the existence of an upper-layer temperature gradient. Some dynamically simpler solutions indicate that the larger-scale disturbances are caused by baroclinic instability. On the other hand, unstable-wave solutions to the linearized instability model suggest that their cause is frontal instability, becoming pure baroclinic instability only when there is no temperature gradient.
• A numerical investigation of jets and eddies near an eastern ocean boundary

  McCreary, J. P, Y. Fukamachi, P. K. Kundu

  Journal of Geophysical Research 96 C2 2515 - 2534 1991年 [査読有り][通常論文]
  

講演・口頭発表等

• サハリン沖係留観測に基づく高精度なAMSR-E薄氷厚アルゴリズムの開発  [通常講演]

  柏瀬陽彦, 大島慶一郎, 深町康, 二橋創平, 田村岳史

  海洋学会秋季大会 富山 2019年09月 口頭発表（一般）
• カービング氷河の融解に伴う海洋への鉄供給過程  [通常講演]

  漢那直也, 杉山慎, 深町康, 野村大樹, 西岡純

  海洋学会秋季大会 富山 2019年09月 口頭発表（一般）
• グリーンランド北西部ボードインフィヨルドにおける氷河近傍での係留観測  [通常講演]

  藤支良貴, 深町康, 漢那直也, 杉山慎

  海洋学会秋季大会 富山 2019年09月 口頭発表（一般）
• グリーンランド北西部ボードイン氷河近傍の海洋における水温，塩分，流速の長期観測  [通常講演]

  藤支 良貴, 深町 康, 漢那 直也, 杉山 慎

  雪氷学会北海道支部研究発表会 2019年05月 口頭発表（一般）
• Interactions between sea-ice drift and near-inertial internal waves in the Northwind Abyssal Plain, Arctic Ocean: year-round mooring observations  [通常講演]

  Yusuke Kawaguchi

  EGU General Assembly 2019 2019年04月 口頭発表（一般）
• Mooring measurement of sea ice and ocean in the northeastern coastal Chukchi Sea from 2009  [招待講演]

  Fukamachi, Y

  Japan-U.S. Arctic Science Collaboration “Reflections on the Past Two Decades and Future Opportunities” 2019年03月 口頭発表（招待・特別）
• HU-UAF collaboration over the past 20 years in the Arctic and Sub-Arctic  [通常講演]

  Saitoh, S, Y. Fukamachi

  Japan-U.S. Arctic Science Collaboration “Reflections on the Past Two Decades and Future Opportunities” 2019年03月 口頭発表（一般）
• Bio-related material cycle in a coastal polynya observed with moored acoustic and optical instruments in the northeastern Chukchi Sea  [通常講演]

  Masato Ito, Kay I. Ohshima, Yasushi Fukamachi, Hajo Eicken, Andrew R. Mahoney, Joshua Jones, Toru Takatsuka

  The Ninth Symposium on Polar Science 2018年12月 口頭発表（一般）
• チュクチ海ポリニヤ域における音響・光学測器による物質循環過程の観測  [通常講演]

  伊藤優人, 大島慶一郎, 深町康, Hajo Eicken,Andrew, R. Mahoney, Joshua Jones

  2018年度日本海洋学会秋季大会 2018年09月 口頭発表（一般） 東京
• グリーンランド北西部におけるカービング氷河前縁フィヨルドの海水特性  [通常講演]

  漢那直也, 杉山慎, 榊原大貴, 深町康, 野村大樹

  2018年度日本海洋学会秋季大会 2018年09月 口頭発表（一般） 東京
• グリーンランド北西部ボードウィンフィヨルドにおける海洋観測  [通常講演]

  藤支良貴, 杉山慎, 漢那直也, 深町康

  雪氷研究大会 2018年09月 ポスター発表 札幌
   

  地震の影響で中止
• 北海道と海氷：海氷の減少とその影響  [通常講演]

  深町康

  バイオミメティクス市民セミナー（第79回）「北海道とバイオミメティクスを考える その3 寒冷地とバイオミメティクス」 2018年07月 公開講演，セミナー，チュートリアル，講習，講義等 札幌
• Effects of glacial meltwater discharge on surface water pCO2 and air–sea CO2 flux in Bowdoin Fjord in northwestern Greenland  [通常講演]

  Daiki Nomura, N. Kanna, S. Yunoki, D. Sakakibara, Y. Fukamachi, T. Hirawake, S. Sugiyama

  Polar 2018 2018年06月 ポスター発表 Davos, Switzerland
• Monitoring of the Soya Warm Current by HF Ocean Radars since 2003  [通常講演]

  Naoto Ebuchi, Yasushi Fukamachi, Kay I. Ohshima, Toru Takatsuka, Masao Ishikawa, Kunio Shirasawa, Masaaki Wakatsuchi

  The 4th Ocean Radar Conference for Asia-Pacific 2018年06月 口頭発表（一般） Naha, Japan
• An evidence of a subglacial freshwater discharge into a fjord at the boundary of Bowdoin Glacier, northwestern Greenland  [通常講演]

  KANNA, Naoya, SUGIYAMA, Shin, SAKAKIBARA, Daiki, FUKAMACHI, Yasushi, NOMURA Daiki, FUKUMOTO, Sungo, PODOLSKIY, Evgeniy

  JpGU Meeting 2018 2018年05月 ポスター発表 Chiba, Japan
• チュクチ海北東部沿岸域における海氷厚の経年変動  [通常講演]

  深町康, 大島慶一郎, Andrew, R. Mahoney, Hajo Eicken, 清水大輔, 岩本勉之, 守家衣利加, 高塚徹, Joshua Jones

  ArCS全体会合 2018年05月 ポスター発表 横浜
• George, Alaska coastal sea ice in the new millennium: Findings from the Seasonal Ice Zone Observing Network and implications for sustained autonomous observations of a rapidly changing Arctic  [通常講演]

  Eicken, Mahoney, Lee, Johnson, Jones, Ohshima, Fukamachi

  2018 Ocean Sciences Meeting 2018年02月 ポスター発表 Portland, USA
• Transports of macronutrient and inorganic carbon to surface waters by subglacial meltwater plume in Bowdoin Fjord in northwest Greenland  [通常講演]

  N. Kanna, S. Sugiyama, Y. Ohashi, D. Sakakibara, B. Nishizawa, I. Asaji, Y. Fukamachi, D. Nomura

  2018 Ocean Sciences Meeting 2018年02月 口頭発表（一般） Portland, USA
• High Ice Production in Antarctic Coastal Polynyas and Its Possible Linkage to Material Cycle and Biological Productivity (Invited)  [通常講演]

  Kay I. Ohshima, Masato Ito, Sohey Nihashi, Yasushi Fukamachi, Kazuki Nakata, Daisuke Simizu

  2018 Ocean Sciences Meeting 2018年02月 ポスター発表 Portland, USA
• Seasonal variability of near-inertial internal waves in the Northwind Abyssal Plain, Arctic Ocean  [通常講演]

  Y. Kawaguchi, M. Itoh, Y. Fukamachi, E. Moriya, N. Onodera, T. Kikuchi

  Fifth International Symposium on Arctic Research (ISAR-5) 2018年01月 口頭発表（一般） Tokyo
• Sea-ice thickness from moored ice-profiling sonar in the Canada Basin, Arctic Ocean  [通常講演]

  Motoyo Itoh, Yasushi Fukamachi, Noriaki Kimura, Richar, A. Krishfield, Takashi Kikuchi, Erika Moriya, Jonaotaro Onodera, Naomi Harada

  Fifth International Symposium on Arctic Research (ISAR-5) 2018年01月 ポスター発表 Tokyo
• Continuous Sea-ice Thickness Measurement in the Northeastern Coastal Chukchi Sea from 2009  [通常講演]

  Y. Fukamachi, K. I. Ohshima, A. R. Mahoney, H. Eicken, D. Simizu, K. Iwamoto, E. Moriya, T. Takatsuka, J. Jones

  Fifth International Symposium on Arctic Research (ISAR-5) 2018年01月 口頭発表（一般） Tokyo
• Sea-ice thickness from moored ice-profiling sonar in the Canada Basin, Arctic Ocean  [通常講演]

  Motoyo Itoh, Yasushi Fukamachi, Noriaki Kimura, Richar, A. Krishfield, Takashi Kikuchi, Erika Moriya, Jonaotaro Onodera, Naomi Harada

  Arctic Change 2017 2017年12月 口頭発表（一般） Québec, Canada
• Mooring measurement in Bowdoin Fjord in northwestern Greenland  [通常講演]

  Yasushi Fukamachi, Naoya Kanna, Shin Sugiyama, Yoshihiko Ohashi, Daiki Sakakibara, Daiki Nomura

  The 8th Symposium on Polar Science 2017年12月 ポスター発表 Tachikawa, Japan
• 急激に変化する北極海の環境とその社会への影響  [通常講演]

  深町康

  北海道大学低温科学研究所公開講座 2017年11月 公開講演，セミナー，チュートリアル，講習，講義等 札幌
• 係留観測による北極海カナダ海盆の海氷厚の季節変動  [通常講演]

  伊東素代, 深町康, 木村詞明, R.A. Krishfield, 菊地隆, 守家衣利加, 小野寺丈尚太郎, 原田尚美

  日本海洋学会2017年度秋季大会 2017年10月 口頭発表（一般） 仙台
• グリーンランド北西部Bowdoinフィヨルドにおける氷河流出水の挙動の時間発展  [通常講演]

  大橋良彦, 青木茂, 松村義正, 杉山慎, 漢那直也, 榊原大貴, 深町康

  日本海洋学会2017年度秋季大会 2017年10月 口頭発表（一般） 仙台
• 氷河融氷水の流出が駆動するグリーンランドフィヨルドにおける栄養塩輸送過程  [通常講演]

  漢那直也, 杉山慎, 大橋良彦, 榊原大貴, 西沢文吾, 浅地泉, 深町康

  日本海洋学会2017年度秋季大会 2017年10月 ポスター発表 仙台
• カービング氷河の高濁度融解水流出がフィヨルド生態系へ与える影響  [通常講演]

  漢那直也, 杉山慎, 大橋良彦, 榊原大貴, 西沢文吾, 浅地泉, 深町康, 阿部義之, 山口篤

  日本雪氷学会 雪氷研究大会2017 2017年09月 ポスター発表 十日町
• Sea Ice Velocity Observation by HF Ocean Radar  [通常講演]

  W. Zhang, N. Ebuchi, Y. Fukamachi, B. Emery

  International Radiowave Oceanography Workshop 2017年09月 口頭発表（一般） Lüneburg, Germany
• グリーンランド北西部ボードイン氷河前縁部における海洋観測  [通常講演]

  漢那直也, 杉山慎, 榊原大貴, 深町康, 野村大樹, 福本俊吾, 山崎新太郎, E. Podolskiy

  北海道大学低温科学研究所共同利用集会 2017年08月 口頭発表（一般） 札幌
• The Suppression Of Antarctic Bottom Water Formation By Melting Ice Shelves In Prydz Bay  [通常講演]

  Guy WILLIAMS, Laura HERRAIZ-BORREGUERO, Fabien ROQUET, Takeshi TAMURA, Kay OHSHIMA, Yasushi FUKAMACHI, Alexander FRASER, Libao GAO, Hongxia CHEN, Clive MCMAHON, Robert HARCOURT, Mark HINDELL

  14th Annual Meeting of Asia Oceania Geosciences Society 2017年08月 ポスター発表 Singapore
• easonal variability of near-inertial internal waves and its kinetic energy in the ice-diminishing Arctic Ocean  [通常講演]

  Yusuke Kawaguchi, Motoyo Itoh, Takashi Kikuchi, Jonaotaro Onodera, Naomi Harada, Yasushi Fukamachi, Erika Moriya

  JpGU-AGU Joint Meeting 2017 2017年05月 ポスター発表 Chiba, Japan
• Effect of subglacial meltwater plume formation on phytoplankton growth in the fjord of Bowdoin Glacier in northwest Greenland  [通常講演]

  Naoya Kanna, Shin Sugiyama, Yoshihiko Ohashi, Daiki Sakakibara, Bungo Nishizawa, Izumi Asaji, Yasushi Fukamachi

  JpGU-AGU Joint Meeting 2017 2017年05月 ポスター発表 Chiba, Japan
• Abrupt changes and interactions of polar oceans and ice sheets as a research subject in Master Plan 2020  [通常講演]

  Shin Sugiyama, Yasushi Fukamachi, Kay I. Ohshima, Shigeru Aoki, Teruo Aoki, Michiyo Yamamoto-Kawai, Takashi Kikuchi, Daisuke Hirano

  JpGU-AGU Joint Meeting 2017 2017年05月 口頭発表（一般） Chiba, Japan
• Subglacial meltwater discharge and its impact on water properties in Bowdoin Fjord, northwestern Greenland  [通常講演]

  Yoshihiko Ohashi, Shigeru Aoki, Yoshimasa Matsumura, Shin Sugiyama, Naoya Kanna, Daiki Sakakibara, Yasushi Fukamachi

  JpGU-AGU Joint Meeting 2017 2017年05月 口頭発表（一般） Chiba, Japan
• Variability of sea-ice thickness in the northeastern coastal Chukchi Sea revealed by a moored ice-profiling sonar  [招待講演]

  Fukamachi Yasushi, Simizu Daisuke, Ohshima Kay, Eicken Hajo, Mahoney Andrew, Iwamoto Katsushi, Moriya Erika, Nihashi Sohey

  JpGU-AGU Joint Meeting 2017 2017年05月 口頭発表（一般） Chiba, Japan
• 北極海の海氷消失が及ぼす北極海の乱流化について – ノースウインド深海平原における係留系データの解析 －  [通常講演]

  川口悠介, 伊東素代, 菊地隆, 小野寺丈尚太郎, 原田尚美, 深町康, 守家衣利加

  ブルーアース2017 2017年03月 ポスター発表 東京
• Sea ice field course at Saroma Lagoon and Okhotsk Sea by International Antarctic Institute  [通常講演]

  Aoki, S, Fukamachi, Y, Toyota, T, Hirawake, T, Mizuta, G, Matsumura, Y, Ohshima, K. I

  The 32nd International Symposium on the Okhotsk Sea & Polar Oceans 2017年02月 口頭発表（一般） Monbetsu, Japan
• Underwater frazil ice formation in the Sakhalin polynya  [通常講演]

  Ito, M, Ohshima, K. I, Fukamachi, Y, Shirasawa, K

  The 32nd International Symposium on the Okhotsk Sea & Polar Oceans 2017年02月 口頭発表（一般） Monbetsu, Japan
• Variability of sea-ice thickness in the northeastern coastal Chukchi Sea revealed by a moored ice-profiling sonar  [通常講演]

  Fukamachi, Y, Simizu, D, Ohshima, K. I, Eicken, H, Mahoney, A. R, Iwamoto, K, Moriya, E, Nihashi, S

  The 32nd International Symposium on the Okhotsk Sea & Polar Oceans 2017年02月 口頭発表（一般） Monbetsu, Japan
• Turbid meltwater discharge and its impact on phytoplankton growth in the fjord of Bowdoin Glacier in northwest Greenland  [通常講演]

  Kanna, N, Sugiyama, S, Ohashi, Y, Sakakibara, D, Nishizawa, B, Asaji, I, Fukamachi, Y

  Workshop on the Dynamics and Mass Budget of Arctic Glaciers & the IASC Network on Arctic Glaciology Annual Meeting 2017年01月 口頭発表（一般） Bethel, USA
• Variability of sea-ice thickness in the northeastern coastal Chukchi Sea revealed by a moored ice-profiling sonar  [通常講演]

  Fukamachi, Y

  Workshop on Sea Ice Remote Sensing and Modeling 2017年01月 口頭発表（一般） Tokyo
• Landfast Sea Ice Breakouts: Stabilizing Ice Features, Oceanic and Atmospheric Forcing at Barrow, Alaska  [通常講演]

  Jones, J, Eicken, H, Manoney, A. R, Kambhamettu, R. MV, C, Fukamachi, Y, Ohshima, K. I, George, C

  2016 AGU Fall Meeting 2016年12月 ポスター発表 San Francisco, USA
• The observation of underwater frazil ice formation and upward sediment transport in an Arctic polynya in the Chukchi Sea  [通常講演]

  Ito, M, Ohshima, K. I, Fukamachi, Y, Simizu D, Mahoney, A. R, Eicken, H

  2016 AGU Fall Meeting 2016年12月 口頭発表（一般） San Francisco, USA
• Modeling glacial meltwater runoff process in Bowdoin Fjord, northwestern Greenland  [通常講演]

  Ohashi Yoshihiko, Aoki Shigeru, Matsumura Yoshimasa, Sugiyama Shin, Kanna Naoya, Sakakibara Daiki, Fukamachi Yasushi

  The Seventh Symposium on Polar Science 2016年12月 ポスター発表 Tachikawa, Japan
• Changes in seabird density relative to oceanographic gradients in the glacial fjord in northwestern Greenland  [通常講演]

  Nishizawa Bungo, Kanna Naoya, Ohashi Yoshihiko, Sakakibara Daiki, Asaji Izumi, Sugiyama Shin, Fukamachi Yasushi, Watanuki Yutaka

  The Seventh Symposium on Polar Science 2016年12月 ポスター発表 Tachikawa, Japan
• Turbid water and chlorophyll a distributions near the interface of the ocean and a tidewater glacier in northwest Greenland  [通常講演]

  Kanna Naoya, Sugiyama Shin, Ohashi Yoshihiko, Sakakibara Daiki, Nishizawa Bungo, Asaji Izumi, Fukamachi Yasushi

  The Seventh Symposium on Polar Science 2016年12月 ポスター発表 Tachikawa, Japan
• Interannual variabilties of fluxes in Barrow Canyon from 2010-2014 : results from the DBO-5 repeat section  [通常講演]

  Itoh Motoyo, Kikuchi Takashi, Fukamachi Yasushi, Pickart Robert, collaborators

  2016 PAG Fall Meeting 2016年10月 口頭発表（一般） Qingdao, China
• サハリンポリニヤにおける過冷却水とフラジルアイスの生成  [通常講演]

  伊藤優人, 大島慶一郎, 深町康

  2016年度日本海洋学会秋季大会 2016年09月 口頭発表（一般） 鹿児島
• 係留観測に基づくAMSR-E薄氷厚アルゴリズムの開発とオホーツク海の海氷生産量マッピング  [通常講演]

  柏瀬陽彦, 大島慶一郎, 深町康, 二橋創平

  2016年度日本海洋学会秋季大会 2016年09月 口頭発表（一般） 鹿児島
• Sea Ice Velocity Observation by HF Ocean Radar  [通常講演]

  張偉, 江淵直人, 深町康, Emery Brian, 程豊, 阿部泰人, 豊田威信, 白澤邦男

  2016年度日本海洋学会春季大会 2016年03月 口頭発表（一般） 東京
• 南極海氷コアから推定される昭和基地周辺の定着氷の発達・崩壊過程  [通常講演]

  豊田威信, 牛尾収輝, 田村岳史, 野村大樹, 清水大輔, 深町康, 松村義正, Fraser Alexander

  2016年度日本海洋学会春季大会 2016年03月 ポスター発表 東京
• アラスカ沖バロー沿岸ポリニヤにおける海氷生産量の経年変動  [通常講演]

  平野大輔, 深町康, 渡邉英嗣, 大島慶一郎, 岩本勉之, Mahoney Andrew, Eicken Hajo, 清水大輔, 田村岳史

  2016年度日本海洋学会春季大会 2016年03月 口頭発表（一般） 東京
• ケープダンレー底層水形成に関わる乱流混合の役割  [通常講演]

  平野大輔, 北出裕二郎, 大島慶一郎, 深町康

  2016年度日本海洋学会春季大会 2016年03月 ポスター発表 東京
• 海氷結氷期における海底堆積物の上方輸送の観測  [通常講演]

  伊藤優人, 大島慶一郎, 西岡純, 楠本仁麦, 水田元太, 深町康

  2016年度日本海洋学会春季大会 2016年03月 口頭発表（一般） 東京
• Formation and Variability of Antarctic Bottom Water off Cape Darnley: the Fourth Antarctic Bottom Water  [通常講演]

  Ohshima, K. I, Nakayama, Y, Fukamachi, Y, Matsumura, Y, Nihashi, S, Tamura, T, Kitade, Y, Hirano, D, Shimizu, D, Aoki S

  2016 AGU Ocean Sciences Meeting 2016年02月 口頭発表（一般） New Orleans, USA
• Observations of frazil ice formation and sediment upward transport off the northeast coast of Sakhalin  [通常講演]

  Ito M, Ohshima, K. I, Nishioka, J, Kusumoto, Y, Mizuta, G, Fukamachi, Y

  The 31th International Symposium on Okhotsk Sea & Sea Ice 2016年02月 口頭発表（一般） Monbetsu, Japan
• Validation of AMSR-E thin ice algorithm based on moored ice profiling sonar measurement  [通常講演]

  Fukamachi, Y, Ohshima, K. I, Iwamoto, K, Tamura, T, Nihashi, S

  Workshop on satellite data for Arctic research and applications, Side event during Arctic Frontiers 2016 2016年01月 口頭発表（一般） Tromsø, Norway
• Sea ice velocity observation by HF radar: Comparison with ADCP and buoy drifter measurements  [通常講演]

  Zhang, W, Ebuchi, N, Emery, B, Fukamachi, Y, Abe, H.. Shirasawa, K.. Toyota,T

  研究集会「海洋レーダーを用いた海況監視システムの開発と応用」 2015年12月 口頭発表（一般） 春日
• ハイブリッド特性を有するバロー沿岸ポリニヤにおける海氷生産量の経年変動  [通常講演]

  平野大輔, 深町康, 渡邉英嗣, 岩本勉之, Andrew Mahoney, Hajo Eicken, 清水大輔, 大島慶一郎, 田村岳史

  第6回極域科学シンポジウム 2015年11月 ポスター発表 立川
• 南極底層水を起点とする熱塩循環・物質循環のダイナミクス  [通常講演]

  大島慶一郎, 川合美千代, 北出裕二郎, 勝又勝郎, 深町康, 田村岳史, 青木茂

  第6回極域科学シンポジウム 2015年11月 口頭発表（一般） 立川
• チャクチ海バロー沖におけるフラジルアイス生成と海底堆積物の上方輸送の観測  [通常講演]

  伊藤優人, 大島慶一郎, 深町康, 清水大輔, Andrew R. Mahoney, Hajo Eicken

  第6回極域科学シンポジウム 2015年11月 口頭発表（一般） 立川
• 北極バロー沖沿岸ポリニヤにおけるフラジルアイスの生成・沈降と堆積物粒子の上方輸送の観測  [通常講演]

  伊藤優人, 大島慶一郎, 深町康, 清水大輔, A. R. Mahoney, H. Eicken

  2015年度日本海洋学会秋季大会 2015年09月 口頭発表（一般） 愛媛
• Sea ice formation on continental shelves: a comparison of water mass signals near an Antarctic ice shelf and off the Alaskan coast  [通常講演]

  Inga J. Smith, Alex J. Gough, Patricia J. Langhorne, Hajo Eicken, Andrew R. Mahoney, Gregory H. Leonard, Robert Van Hale, Yasushi Fukamachi, Stefan Jendersie, Joshua Jones, Timothy G. Haskell

  IGS International Symposium on Contemporary Ice-Sheet Dynamics 2015年08月 口頭発表（一般） Cambridge, UK
• Numerical Investigation of Formation and Variability of Antarctic Bottom Water off Cape Darnley  [通常講演]

  Nakayama, Y, Ohshima, K. I, Matsumura, Y, Fukamachi, Y, Hiroyasu, H

  26th IUGG General Assembly 2015 2015年07月 口頭発表（一般） Prague, Czech Republic
• The fourth Antarctic Bottom Water: Cape Darnley Bottom Water  [通常講演]

  Ohshima, K. I, Fukamachi, Williams, G. D, Nihashi, S, Tamura, T, Kitade, Y, Hirano, D, Aoki, S, Wakatsuchi, M

  26th IUGG General Assembly 2015 2015年07月 口頭発表（一般） Prague, Czech Republic
• A wind-driven, hybrid latent and sensible heat coastal polynya at Barrow, Alaska  [通常講演]

  Hirano, D, Y. Fukamachi, E. Watanabe, K. Iwamoto, A. R. Mahoney, H. Eicken, D. Simizu, K. I. Ohshima, T. Tamura

  26th IUGG General Assembly 2015 2015年06月 口頭発表（一般） Prague, Czech Republic
• Sediment upward dispersion and frail ice formation by strong wnd events -A possible mechanism of iron supply to sea ice  [通常講演]

  Ito, M, K. I. Ohshima, J. Nishioka, Y. Kusumoto, G. Mizuta, Y. Fukamachi

  ESSAS Annual Science Meeting 2015年06月 口頭発表（一般） Seattle, USA
• Characteristics of sea-ice draft revealed by a moored ice-profiling sonar in the Chukchi Sea off Barrow, Alaska  [通常講演]

  Fukamachi. Y, Simizu, D, Ohshima, K. I, Iwamoto, K, Eicken, H, Mahoney, A. R

  Fourth International Symposium on the Arctic Research (ISAR-4) 2015年04月 ポスター発表 Toyama
• SIZONet: Multi-purpose, multi-platform observations to inform responses to an Arctic sea ice cover in transformation  [通常講演]

  Eicken, H, Mahoney, A. R, Dammann, D. O, Jones, J, Hendricks, S, Fukamachi, Y, Ohshima, K. I, Haas, C, Gerland, S, Makshtas, A

  Fourth International Symposium on the Arctic Research (ISAR-4) 2015年04月 ポスター発表 Toyama
• A wind-driven, hybrid latent and sensible heat coastal polynya at Barrow, Alaska  [通常講演]

  Hirano, D, Y. Fukamachi, E. Watanabe, K. Iwamoto, A. R. Mahoney, H. Eicken, D. Simizu, K. I. Ohshima, T. Tamura

  Forth International Symposium on the Arctic Research (ISAR-4) 2015年04月 口頭発表（一般） Toyama
• 強風イベントによる海底堆積物の上方輸送とフラジルアイス生成-海氷への鉄供給メカニズム-  [通常講演]

  伊藤優人, 大島慶一郎, 西岡純, 楠本仁麦, 水田元太, 深町康

  2015年度日本海洋学会春季大会 2015年03月 口頭発表（一般） 東京
• 係留観測による北極チャクチ海沿岸域の海氷厚に関する研究  [通常講演]

  守家衣利加, 深町康, 清水大輔, 大島慶一郎, 高塚徹, 岩本勉之, Mahoney Andrew R, Jones Joshua, Eicken Hajo

  2015年度日本海洋学会春季大会 2015年03月 口頭発表（一般） 東京
• ビンセネス湾沖における南極底層水の特性  [通常講演]

  北出裕二郎, 嶋田啓資, 白井優, 青木茂, 深町康, 田村岳史, 牛尾収輝, 大島慶一郎

  2015年度日本海洋学会春季大会 2015年03月 口頭発表（一般） 東京
• アラスカ沖バロー沿岸ポリニヤの特徴（Ⅱ）  [通常講演]

  平野大輔, 深町康, 渡邉英嗣, 岩本勉之, MahoneAndrew, Eicken Hajo, 清水大輔, 大島慶一郎, 田村岳史

  2015年度日本海洋学会春季大会 2015年03月 口頭発表（一般） 東京
• リュツォ・ホルム湾定着氷域での海氷厚の分布と変動  [通常講演]

  杉本風子, 大島慶一郎, 田村岳史, 宇都正太郎, 下田春人, 清水大輔, 舘山一孝, 星野聖太, 深町康, 尾関俊浩, 牛尾収輝

  2015年度日本海洋学会春季大会 2015年03月 ポスター発表 東京
• Sediment upward dispersion and frazil ice formation by strong windy events in the Sea of Okhotsk observed with ADCP. －A possible mechanism of iron supply to sea ice－  [通常講演]

  Ito, M, Ohshima, K. I, Nishioka, J, Kusumoto, Y, Mizuta, G, Fukamachi, Y

  The 30th International Symposium on Okhotsk Sea & Sea Ice 2015年02月 ポスター発表 Monbetsu, Japan
• チャクチ海アラスカバロー沖における海氷厚の係留観測  [通常講演]

  守家衣利加, 深町康, 清水大輔, 大島慶一郎, 高塚徹, 岩本勉之, Mahoney Andrew R, Jones Joshua, Eicken Hajo

  第5回極域科学シンポジウム 2014年12月 ポスター発表 立川
• アラスカ沖バロー沿岸ポリニヤの特徴  [通常講演]

  平野大輔, 深町康, 渡邉英嗣, 岩本勉之, Andrew Mahoney, Hajo Eicken, 清水大輔, 大島慶一郎, 田村岳史

  第5回極域科学シンポジウム 2014年12月 ポスター発表 立川
• ビンセネス湾沖南極底層水の特性  [通常講演]

  北出裕二郎, 嶋田啓資, 白井優, 青木茂, 田村岳史, 深町康, 牛尾収輝, 大島慶一郎

  第5回極域科学シンポジウム 2014年12月 口頭発表（一般） 立川
• A wind-driven, hybrid latent and sensible heat coastal polynya at Barrow, Alaska  [通常講演]

  Hirano, D, Y. Fukamachi, E. Watanabe, K. Iwamoto, A. Mahoney, H. Eicken, D. Shimizu, K. I. Ohshima, T. Tamura

  AGU Fall Meeting 2014 2014年11月 ポスター発表 San Francisco, USA
• アラスカ沖バロー沿岸ポリニヤの特徴（Ⅰ）  [通常講演]

  平野大輔, 深町康, 渡邉英嗣, 岩本勉之, Andrew Mahoney, Hajo Eicken, 清水大輔, 大島慶一郎, 田村岳史

  2014年度日本海洋学会秋季大会 2014年09月 口頭発表（一般） 長崎
• Antarctic Bottom Water production from intense sea-ice formation in the Cape Darnley Polynya  [招待講演]

  Ohshima, K. I, Y. Fukamachi, G. D. Williams, S. Nihashi, T. Tamura, Y. Kitade, D. Hirano, S. Aoki, M. Wakatsuchi

  11th Annual Meeting, Asia Oceania Geosciences Society 2014年08月 口頭発表（招待・特別） Sapporo, Japan
• 第4の南極底層水：ケープダンレー底層水  [通常講演]

  大島慶一郎, 深町康, Williams, G. D, 二橋創平, 田村岳史, 北出裕二郎, 平野大輔, 青木茂, 若土正曉

  日本地球惑星科学連合2014年大会 2014年05月 口頭発表（一般） 横浜
• ビンセネス湾沖南極底層水の流動特性について  [通常講演]

  白井優, 北出裕二郎, 嶋田啓資, 青木茂, 深町康, 大島慶一郎

  2014年度日本海洋学会春季大会 2014年03月 口頭発表（一般） 東京
• アラスカバロー沖チャクチ海ポリニヤにおける海氷・海洋の係留観測  [通常講演]

  深町康, 大島慶一郎, 清水大輔, 伊藤優人, 岩本勉之, 松村義正, Eicken, H, Mahoney, A. R

  2014年度日本海洋学会春季大会 2014年03月 口頭発表（一般） 東京
• Antarctic and Arctic land-fast sea ice: deriving parent water mass properties changes from sea ice cores  [通常講演]

  I. J. Smith, A. J. Gough, P. J. Langhorne, H. Eicken, A. R. Mahoney, G. H. Leonard, R. J. Van Hale, Y. Fukamachi, S. Jendersie, J. M. Jones, T. G. Haskell

  IGS International Symposium on Sea Ice in a Changing Environment 2014年03月 口頭発表（一般） Hobart, Australia
• Taking a look at both sides of the ice: comparing ice thickness and drift speed as observed from above and below sea ice near Barrow, Alaska  [通常講演]

  A. R. Mahoney, H. Eicken, Y. Fukamachi, K. I. Ohshima, D. Simizu, C. Kambhamettu, R. MV, S. Hendricks, J. Jones

  IGS International Symposium on Sea Ice in a Changing Environment 2014年03月 口頭発表（一般） Hobart, Australia
• Characteristics of sea-ice draft revealed by a moored ice-profiling sonar in the Chukchi Sea off Barrow, Alaska  [通常講演]

  Y. Fukamachi, D. Simizu, K. I. Ohshima, K. Iwamoto, H. Eicken, A. R. Mahoney

  IGS International Symposium on Sea Ice in a Changing Environment 2014年03月 口頭発表（一般） Hobart, Australia
• Distribution and interannual variability of sea-ice thickness in the pack-ice zone off Lützow-Holm Bay, Antarctica  [通常講演]

  F. Sugimoto, H. Shimoda, D. Simizu, S. Uto, K. Tateyama, S. Hoshino, T. Ozeki, T. Tamura, Y. Fukamachi, S. Ushio, K. I. Ohshima

  IGS International Symposium on Sea Ice in a Changing Environment, 2014年03月 ポスター発表 Hobart, Australia
• A study of formation processes of supercooled water and frazil ice in a coastal polynya  [通常講演]

  Ito M, K. I. Ohshima, Y. Fukamachi, D. Simizu, K. Iwamoto, Y. Matsumura, A. R. Mahoney, H. Eicken

  IGS International Symposium on Sea Ice in a Changing Environment 2014年03月 口頭発表（一般） Hobart, Australia
• A study of formation processes of supercooled water and frazil ice in a coastal polynya  [通常講演]

  Ito M, K. I. Ohshima, Y. Fukamachi, D. Simizu, K. Iwamoto, Y. Matsumura, A. R. Mahoney, H. Eicken

  The 29th International Symposium on Okhotsk Sea & Sea Ice 2014年02月 口頭発表（一般） 紋別
• 沿岸ポリニヤにおける過冷却水およびフラジルアイス生成過程についての研究  [通常講演]

  伊藤優人, 大島慶一郎, 深町康, 清水大輔, 岩本勉之, 松村義正, Mahoney, A. R, Eicken,H

  第4回極域科学シンポジウム 2013年11月 ポスター発表
• 2010年夏季北極海バロー海底谷における熱輸送  [通常講演]

  伊東素代, 菊地隆, 深町康, Pickart, R, 大島慶一郎, 清水大輔, Arrigo, K, Vagle, S, He, J, Ashjian, C

  2013年度日本海洋学会秋季大会 2013年09月 口頭発表（一般）
• 沿岸ポリニヤにおける過冷却水およびフラジルアイス生成過程についての研究  [通常講演]

  伊藤優人, 大島慶一郎, 深町康, 清水大輔, 岩本勉之, 松村義正, Mahoney, A. R, Eicken,H

  2013年度日本海洋学会秋季大会 2013年09月 口頭発表（一般）
• 昭和基地沖流氷域での海氷厚観測  [通常講演]

  杉本風子, 下田春人, 清水大輔, 宇都正太郎, 舘山一孝, 星野聖太, 尾関俊浩, 田村岳史, 深町康, 牛尾収輝, 大島慶一郎

  2013年度日本海洋学会秋季大会 2013年09月 口頭発表（一般）
• ビンセネス湾ポリニヤにおける高密度陸棚水の生成について  [通常講演]

  北出裕二郎, 嶋田啓資, 田村岳史, 深町 康, 青木 茂, 牛尾 収輝, 大島 慶一郎

  2013年度日本海洋学会秋季大会 2013年09月 口頭発表（一般）
• 第4の南極底層水: Cape Danley Bottom Water  [通常講演]

  大島慶一郎, 深町康, Williams, G. D, 二橋創平, 北出裕二郎, 平野大輔, 田村岳史, 青木茂, 若土正

  2013年度日本海洋学会秋季大会 2013年09月 口頭発表（一般）
• 急激に変わりゆく北極海  [招待講演]

  菊地隆, 原田尚美, 深町康

  2013年度日本海洋学会秋季大会 2013年09月 口頭発表（一般） 札幌
• ビンセネス湾沖南極底層水の流動特性について  [通常講演]

  白井優, 北出裕二郎, 嶋田啓資, 青木茂, 深町康, 大島慶一郎

  2014年度日本海洋学会春季大会 2013年03月 口頭発表（一般） 東京
• 北極海バロー沖における海氷厚直接観測  [通常講演]

  清水大輔, 深町康, 大島慶一郎, 岩本勉之

  2013年度日本海洋学会春季大会 2013年03月 口頭発表（一般）
• ビンセネス湾沖での係留観測により捉えられた南極底層水の特性  [通常講演]

  北出裕二郎, 嶋田啓資, 田村岳史, 深町 康, 青木 茂, 牛尾収輝, 大島慶一郎

  第35回極域気水圏シンポジウム 2012年11月 口頭発表（一般）
• サハリン沖での係留系氷厚データとの直接比較によるAMSR-E薄氷厚アルゴリズムの作成  [通常講演]

  柏瀬陽彦, 大島慶一郎, 深町康, 二橋創平

  2012年度日本海洋学会秋季大会 2012年09月 口頭発表（一般）
• ビンセネス湾沖で係留観測によって捉えた南極底層水の特性  [通常講演]

  北出裕二郎, 嶋田啓資, 田村岳史, 深町康, 青木茂, 大島慶一郎, 牛尾収輝

  日仏海洋学会学術研究発表会 2012年06月 口頭発表（一般）
• ケープダンレープロジェクト～第4の南極底層水起源域の同定  [通常講演]

  深町康, 清水大輔, 大島慶一郎, 小野数也, 田村岳史, 青木茂, 北出裕一郎, 平野大輔, 牛尾収輝, 橋田元

  2012年度日本海洋学会春季大会 2012年03月 口頭発表（一般）
• 南極海ケープダンレーポリニヤにおける海氷・海洋の係留観測  [通常講演]

  深町康, 清水大輔, 大島慶一郎, 小野数也, 田村岳史, 青木茂, 牛尾収輝, 橋田元

  第34回極域気水圏シンポジウム 2011年11月 口頭発表（一般）
• 南極海ケープダンレーポリニヤにおける海氷・海洋の係留観測  [通常講演]

  深町康, 清水大輔, 大島慶一郎, 小野数也, 田村岳史, 青木茂, 牛尾収輝, 橋田元

  第2回極域科学シンポジウム 2011年11月 口頭発表（一般）
• 南極昭和基地における験潮儀とGPSブイで観測された潮位変化の比較  [通常講演]

  青山雄一, 深町康, 土井浩一郎, 青木茂, 渋谷和雄

  日本測地学会第116回講演会 2011年10月 口頭発表（一般）
• 南極海ケープダンレーポリニヤにおける海氷・海洋の係留観測  [通常講演]

  深町康, 清水大輔, 大島慶一郎, 小野数也, 田村岳史, 青木茂, 牛尾収輝, 橋田元

  2011年度日本海洋学会秋季大会 2011年09月 口頭発表（一般）
• ケープダンレー沖における南極底層水の形成と流動に関する数値的研究  [通常講演]

  中山佳洋, 大島慶一郎, 松村義正, 羽角博康, 深町康

  2011年度日本海洋学会春季大会 2011年03月 口頭発表（一般）
• Polynya formation and sea ice production off Cape Darnley Antarctica, revealed by ALOS PALSAR and AMSR-E data  [通常講演]

  Ohshima, K. I, S. Nihashi, T. Tamura, Y. Fukamachi

  4th ALOS Joint PI Symposium 2010年11月 口頭発表（一般）
• 海氷厚・南極底層水の係留系観測 －温暖化で氷厚・底層水は変化しているか？－  [通常講演]

  大島慶一郎, 深町康, 牛尾収輝, 橋田元, 青木茂, 清水大輔, 小野数也

  南極観測シンポジウム 2010年09月 口頭発表（一般）
• オホーツク海の海氷が水塊形成・熱塩収支及びその変動に与えるインパクト  [通常講演]

  大島慶一郎, 中野渡拓也, 深町 康, 若土正曉, 二橋創平, S. C. Riser

  2010年度日本海洋学会秋季大会 2010年09月 口頭発表（一般） 網走
• 海氷と沿岸海洋の相互作用による海氷漂流強化機構  [通常講演]

  中山佳洋, 大島慶一郎, 深町康

  2010年度日本海洋学会秋季大会 2010年09月 口頭発表（一般） 網走
• 宗谷暖流の流速の短周期変動の下流方向への伝播  [通常講演]

  江淵直人, 深町 康, 大島慶一郎

  2010年度日本海洋学会秋季大会 2010年09月 口頭発表（一般） 網走
• Antarctic Bottom Water revealed by mooring measurements off Cape Darnley, Antarctica  [通常講演]

  Fukamachi, Y, K. I. Ohshima, S. Aoki, Y. Kitade, T. Tamura, M. Wakatsuchi

  International Polar Year Oslo Science Conference 2010年06月 口頭発表（一般） Oslo (Norway)
• Characteristics of ice in the Okhotsk coastal polynyas  [通常講演]

  Sohey Nihashi, Naoto Ebuchi, Shuhei Takahashi, Yasushi Fukamachi

  INTERNATIONAL SYMPOSIUM ON SEA ICE IN THE PHYSICAL AND BIOGEOCHEMICAL SYSTEM 2010年06月 ポスター発表 Tromoso, Norway
• ケープダンレー沖で観測された南極底層水の特性と分布  [通常講演]

  北出裕二郎, 平野大輔, 大島慶一郎, 深町康

  2010年度日本海洋学会春季大会 2010年03月 口頭発表（一般） 東京
• 係留観測による南極海ケープダンレー沖における南極底層水について  [通常講演]

  深町康, 大島慶一郎, 青木茂, 北出裕二郎, 田村岳史, 若土正曉

  2010年度日本海洋学会春季大会 2010年03月 口頭発表（一般） 東京
• 新たに発見された南極底層水とそれに関わる海氷生産の直接観測－ケープダンレープロジェクト－  [通常講演]

  大島慶一郎, 深町康

  2010年度日本海洋学会春季大会 2010年03月 口頭発表（一般） 東京
• 枝幸沖水温の十数日変動  [通常講演]

  西田芳則, 田中伊織, 深町康, 大島慶一郎

  2010年度日本海洋学会春季大会 2010年03月 口頭発表（一般） 東京
• Creation of heat/salt flux data set in the Okhotsk Sea using AMSR-E sea ice data.  [通常講演]

  Ohshima, K. I, T. Tamura, S. Nihashi, K. Iwamoto, D. Simizu, Y. Fukamachi

  US CLIVAR/SeaFlux Workshop, Surface Fluxes: Challenges for High Latitudes 2010年03月 ポスター発表 アメリカ・ボルダー
• 海鷹丸によりダンレー沖で観測された深底層水の特性と海洋微細構造  [通常講演]

  北出裕二郎, 平野大輔, 大島慶一郎, 深町康

  第32回極域気水圏シンポジウム 2009年11月 口頭発表（一般） 立川
• 係留観測による南極海ケープダンレー沖における南極底層水の変動について  [通常講演]

  深町康, 大島慶一郎, 青木茂, 北出裕二郎, 田村岳史

  第32回極域気水圏シンポジウム 2009年11月 口頭発表（一般） 立川
• ケープダンレープロジェクト －新たに発見された南極底層水とそれに関わるか海氷生産の直接観測  [通常講演]

  大島慶一郎, 深町康

  第32回極域気水圏シンポジウム 2009年11月 口頭発表（一般） 立川
• 宗谷暖流の構造・流量の季節・経年変動  [通常講演]

  大島慶一郎, 森島秀太, 清水大輔, 江淵直人, 深町康, 若土正曉, Y. Volkov

  2009年度日本海洋学会秋季大会 2009年09月 口頭発表（一般） 京都
• 南極海インド洋セクターのケルゲレン海台東側斜面域における南極底層水流量の時間変動  [通常講演]

  深町康, Stephen R. Rintoul・John, A. Church, 青木茂, Serguei Sokolov, Mark A. Rosenberg, 若土正曉

  2009年度日本海洋学会秋季大会 2009年09月 口頭発表（一般） 京都
• GSOP report, The 5th meeting of the CLIVAR Southern Ocean Panel  [通常講演]

  Fukamachi, Y

  2009年02月 口頭発表（一般） University of New South Wales, Sydney, Australia
• A trial of prediction of paralytic shellfish poisoning along the coast of Hokkaido in the Okhotosk Sea  [通常講演]

  Shimada, H, M. Sawada, I. Tanaka, H. Asami, Y. Fukamachi

  The 24th International Symposium on Okhotsk Sea and Sea Ice 2009年02月 口頭発表（一般） Shimada, H., M. Sawada, I. Tanaka, H. Asami, and Y. Fukamachi: A trial of prediction of paralytic shellfish poisoning along the coast of Hokkaido in the Okhotosk Sea, The 24th International Symposium on Okhotsk Sea and Sea Ice, Mombetsu Arts & Culture Cen
• Mooring measurement of the deep western boundary current over the eastern flank of the Kerguelen Plateau in the Indian Sector of the Antarctic  [通常講演]

  Fukamachi, Y, S. Aoki, J. A. Church, S. R. Rintoul, M. Rosenberg, M. Wakatsuchi

  9th International Conference of the Southern Hemisphere Meteorology 2009年02月 口頭発表（一般） Melbourne Convention Center, Melbourne
• Sea ice production in the polynya and the associated bottom water formation off the Cape Darnley, East Antarctica  [通常講演]

  Ohshima, K. I, T. Tamura, Y. Fukamachi, S. Aoki

  9th International Conference of the Southern Hemisphere Meteorology and Oceanography 2009年02月 口頭発表（一般） Melbourne Convention Center, Melbourne
• 南極海インド洋セクターのケルゲレン海台東側斜面域における南極底層水の流量  [通常講演]

  深町康, 青木茂・John A. Church, Stephen R. Rintoul, Mark Rosenberg, 若土正曉

  第31回極域気水圏・生物圏合同シンポジウム 2008年12月 口頭発表（一般） 東京
• HF-radar technology in the Sea of Okhotsk  [通常講演]

  Ebuchi, N, Y. Fukamachi, K. I. Ohshima, M. Wakatsuchi

  Fourth PICES (North Pacific Marine Science Organization) Workshop on the Okhotsk and adjacent areas 2008年08月 口頭発表（一般） Abashiri
• Interannual material fluxes under seasonal sea ice in the Okhotsk Sea north of Hokkaido, Japan  [通常講演]

  Hiwatari, T, H. Koshikawa, K. Kohata, Y. Fukamachi, K. Shirasawa

  Fourth PICES (North Pacific Marine Science Organization) Workshop on the Okhotsk and adjacent areas 2008年08月 口頭発表（一般） Abashiri
• Downslope Mixing of Antarctic Bottom Water from East Antarctic Polynyas  [通常講演]

  G. Williams, S. Aoki, S. Marsland, Y. Fukamachi, B. Galton-Fenzi, S. Rintoul, N. Bindoff

  SCAR/IASC 2008年07月 口頭発表（一般） St. Petersburg, Russia
• オホーツク海サハリン北部沖における海氷厚の係留観測  [通常講演]

  深町康, 白澤邦男, 大島慶一郎, 水田元太, 若土正曉

  2008年度日本海洋学会春季大会 2008年03月 口頭発表（一般） 東京
• 夏季北海道オホーツク海沿岸における麻痺性貝毒発生予測の試み  [通常講演]

  嶋田宏, 澤田真由美, 田中伊織, 浅見大樹, 深町康

  2008年度日本海洋学会春季大会 2008年03月 ポスター発表 東京
• HFレーダによる宗谷暖流の観測  [通常講演]

  江淵 直人, 深町康, 大島慶一郎, 白澤邦男, 石川正雄, 高塚徹, 若土正曉

  九州大学応用力学研究所研究集会 2007年12月 口頭発表（一般） 春日、福岡
• Impact of sea-ice variability on physical and biological processes in the Sea of Okhotsk  [通常講演]

  Ohshima, K. I, Y. Fukamachi, T. Nakanowatari, T. Nakatsuka, J. Nishioka, M. Wakatsuchi

  The Second Annual Meeting of the GLOBEC 2007年06月 口頭発表（一般） 函館
• Short-term variation in the Soya Warm Current observed by HF ocean radars and coastal tide gauges  [通常講演]

  Ebuchi, N, Y. Fukamachi, K. I. Ohshima, M. Wakatsuchi

  Radiowave Oceanography The 8th International Workshop 2007年05月 口頭発表（一般） Cancun, Mexico
• 短波海洋レーダおよび沿岸潮位計で観測された宗谷暖流の短周期変動について  [通常講演]

  江淵直人, 深町康, 大島慶一郎, 若土正曉

  海洋理工学会平成19年度春季大会 2007年05月 口頭発表（一般） 東京
• 海底設置ADCPと海洋レーダを用いた宗谷暖流流量の見積り  [通常講演]

  深町康, 田中伊織, 大島慶一郎, 江淵直人, 水田元太, 吉田英雄, 若土正曉

  九州大学応用力学研究所研究集会 2006年12月 口頭発表（一般） 春日、福岡
• HFレーダによる宗谷暖流の観測  [通常講演]

  江淵直人, 深町康, 大島慶一郎, 白澤邦男, 石川正雄, 高塚徹, 若土正曉

  九州大学応用力学研究所研究集会 2006年12月 口頭発表（一般） 春日、福岡
• OOPC (Ocean Observations Panel for Climate) updates and links to panel  [通常講演]

  Fukamachi, Y

  The 4th CLIVAR (Climate Variability and Predictability) Southern Ocean Panel Meeting 2006年11月 口頭発表（一般） Buenos Aires, Argentina
• Variations in the Soya Warm Current observed by HF ocean radar, coastal tide gauges and satellite altimetry  [通常講演]

  Ebuchi, N, Y. Fukamachi, K. I. Ohshima, K. Shirasawa, M. Wakatsuchi

  International Symposium on Remote Sensing 2006年11月 口頭発表（一般） Busan, Korea
• 海底設置ADCPによる宗谷暖流の長期連続観測  [通常講演]

  深町康, 大島慶一郎, 江淵直人, 水田元太, 若土正曉

  2006年度日本海洋学会秋季大会 2006年09月 口頭発表（一般） 名古屋
• Observation of the Soya Warm Current combining HF ocean radar with coastal tide gauges and satellite altimetry  [通常講演]

  Ebuchi, N, Y. Fukamachi, K. I. Ohshima, K. Shirasawa, M. Wakatsuchi

  IEEE International Geoscience and Remote Sensing 2006年07月 口頭発表（一般） Denver, U.S.A.
• Japanese mooring plan in the Cape Darnley polynya during the International Polar Year  [通常講演]

  Fukamachi, Y, K. I. Ohshima, S. Aoki, S. Ushio, M. Wakatsuchi

  International Workshop on Antarctic Sea Ice Thickness 2006年07月 口頭発表（一般） Hobart, Australia
• Observation of the Soya Warm Current using HF ocean radars  [通常講演]

  Ebuchi, N, Y. Fukamachi, K. I. Ohshima, K. Shirasawa, M. Wakatsuchi

  Radiowave Oceanography The 7th International Workshop 2006年05月 口頭発表（一般） Hamburg, Germany
• 南極海インド洋セクターのケルゲレン海台東側斜面における深層西岸境界流の係留観測  [通常講演]

  深町康, 青木茂, 若土正曉

  2006年度日本海洋学会春季大会 2006年03月 口頭発表（一般） 横浜
• 短波海洋レーダ・沿岸潮位記録・衛星高度計などを用いた宗谷暖流のモニタリング  [通常講演]

  江淵直人, 深町康, 大島慶一郎, 白澤邦男, 若土正曉

  2006年度日本海洋学会春季大会 2006年03月 口頭発表（一般） 横浜
• Diurnal Coastal-Trapped Waves on the Eastern Shelf of Sakhalin in the Okhotsk Sea  [通常講演]

  Ono, J, K. I. Ohshima, G. Mizuta, Y. Fukamachi, M. Wakatsuchi

  American Geophysical Union (AGU) Ocean Sciences Meeting 2006年02月 ポスター発表 Honolulu, Hawaii, U.S.A.
• 南極海インド洋セクターのケルゲレン海台東側斜面における深層西岸境界流の係留観測  [通常講演]

  深町康, 青木茂, 若土正曉

  第28回極域気水圏シンポジウム 2005年11月 口頭発表（一般） 東京
• 短波海洋レーダ・沿岸潮位記録・衛星高度計などを用いた宗谷暖流のモニタリング  [通常講演]

  江淵直人, 深町康, 大島慶一郎, 白澤邦男, 若土正曉

  海洋理工学会平成17年度秋季大会 2005年10月 口頭発表（一般） 京都
• 北海道オホーツク海沿岸域で発達する季節海氷はなにをもたらすのか？ -セジメントトラップフラックスデータから-  [通常講演]

  樋渡武彦, 深町康, 白澤邦男, 永田隆一, 越川海, 木幡邦男, 渡辺正孝

  日本プランクトン学会 2005年09月 口頭発表（一般）
• Observation of the Soya Warm Current using HF Ocean Radar  [通常講演]

  Ebuchi, N, Y. Fukamachi, K. I. Ohshima, K. Shirasawa, M. Wakatsuchi

  Radiowave Oceanography 6th International Workshop 2005年05月 口頭発表（一般） Santa Cruz, U.S.A.
• カラフト東岸沖における潮流特性と日周潮陸棚波  [通常講演]

  小野純, 大島慶一郎, 水田元太, 深町康, 若土正曉

  2005年度日本海洋学会春季大会 2005年03月 口頭発表（一般） 東京
• Seasonal variation of the Soya Warm Current observed by HF ocean radar  [通常講演]

  Ebuchi, N, Y. Fukamachi, K. I. Ohshima, K. Shirasawa, M. Ishikawa, T. Takatsuka, T. Daibo, M. Wakatsuchi

  International Symposium on Remote Sensing (ISRS) 2004年10月 Jeju, Korea
• Observations of the Soya Warm Current using HF Ocean Radar  [通常講演]

  Ebuchi, N, Y. Fukamachi, K. I. Ohshima, K. Shirasawa, M. Ishikawa, T. Takatsuka, T. Daibo, M. Wakatsuchi

  IEEE International Geoscience and Remote Sensing Symposium (IGARSS) 2004年09月 Anchorage, Alaska
• 短波海洋レーダによる宗谷暖流の観測  [通常講演]

  江淵直人, 深町康, 大島慶一郎, 白澤邦男, 若土正曉

  2004年日本海洋学会春季大会 2004年03月 口頭発表（一般） つくば

作品等

• 海洋研究開発機構学術研究船「白鳳丸」KH-07-4次航海

  2008年
• 江淵 直人・深町 康・大島 慶一郎・白澤 邦男・石川 正雄・高塚 徹・若土正曉：短波海洋レーダ・沿岸潮位記録・衛星高度計などを用いた宗谷暖流のモニタリング

  2006年
• Fukamachi, Y. on behalf of Southern Ocean panel: Southern Ocean CLIVAR/CliC/SCAR panel, The 11th Session of Ocean Observations Panel for Climate (OOPC-11), Tokyo, Japan

  2006年

その他活動・業績

• 北極海ノースウィンド深海平原における海氷厚の季節変動

  上野威, 上野洋路, 上野洋路, 伊東素代, 渡邉英嗣, 小野寺丈尚太郎, 川口悠介, 藤尾伸三, 守家衣利加, 深町康 日本海洋学会大会講演要旨集(Web) 2022 2022年
• グリーンランド北西部ボードイン氷河前縁フィヨルドにおける水温・塩分・流速の長期係留観測

  藤支良貴, 深町康, 漢那 直也, 杉山 慎 北海道の雪氷 38 15 -18 2019年09月 [査読無し][通常論文]
  
• 極域海洋モニタリングブイの開発‐オホーツク海における試験観測

  青木茂, 市川雅明, 市川雅明, 小野数也, 深町康, 深町康, 深町康, 大島慶一郎, 大島慶一郎, 中川敏彦, 小林研吾, 小竹正人, 小竹正人, 小澤知史 海洋理工学会誌(Web) 25 (1) 29‐34(J‐STAGE) 2019年 [査読無し][通常論文]
  
• 氷河融氷水の流出が駆動するグリーンランドフィヨルドにおける栄養塩輸送過程

  漢那直也, 杉山慎, 杉山慎, 大橋良彦, 榊原大貴, 西沢文吾, 浅地泉, 深町康, 深町康 日本海洋学会大会講演要旨集 2017 274 2017年09月 [査読無し][通常論文]
  
• カービング氷河の高濁度融解水流出がフィヨルド生態系へ与える影響

  漢那直也, 杉山慎, 杉山慎, 大橋良彦, 榊原大貴, 西沢文吾, 浅地泉, 深町康, 深町康, 阿部義之, 山口篤 雪氷研究大会講演要旨集(Web) 2017 (0) 286(J‐STAGE) -286 2017年 [査読無し][通常論文]
  
• 南大洋の深層水形成と海氷過程 海鷹丸により観測されたケープダンレー沖の南極底層水と海洋微細構造の特徴

  北出裕二郎, 平野大輔, 大島慶一郎, 深町康 月刊海洋 29 -36 2010年06月01日 [査読無し][通常論文]
  
• 未知の南極底層水生成域の発見と今後の観測に向けて―ケープダンレープロジェクト―

  大島慶一郎, 深町康, 青木茂, 清水大輔, 田村岳史, 牛尾収輝, 橋田元, 北出裕二郎, 若土正暁 月刊海洋 総特集「南大洋の深層水形成と海氷過程」 54、12-20 2010年 [査読無し][通常論文]
  
• サハリン東岸沖での長期係留観測結果 : 高密度陸棚水の流量見積もり

  深町 康, 水田 元太, 大島 慶一, 若土 正暁 Otsuchi marine science = 東京大学海洋研究所大槌臨海研究センター研究報告 27 (27) 70 -71 2002年03月29日 [査読無し][通常論文]
   

  平成13年度共同利用研究集会「北太平洋北西部とその縁辺海の水塊変動と循環」（2001年8月21日, 研究代表者：岩坂直人）講演要旨
• オホーツク海南西部の冬季の海洋構造とその海氷との関係

  大島 慶一郎, 水田 元太, 伊東 素代, 深町 康, 渡辺 達郎, 難波 江靖, 末広 孝吉, 若土 正暁, Kay I. Ohshima, Genta Mizuta, Motoyo Itoh, Yasushi Fukamachi, Tatsuro Watanabe, Yasushi Nabae, Koukichi Suehiro, Masaaki Wakatsuchi 海の研究 = Umi no Kenkyu (Oceanography in Japan) 11 (2) 368 -368 2002年03月05日 

  オホーツク海南西部において,1997年2月砕氷船「そうや」により,海洋と海氷の観測を行った。この観測によって,ほぼ結氷温度にある海洋混合層が300mの深さにまで達しているのが見つかった。これは,今まで考えられていたよりもずっと深い。この深い海洋混合層はこの海域で形成されたのではなく,サハリン東岸沖で形成され,それが東サハリン海流によって陸棚斜面に沿って移流されたものであると考えられる。また,これらと一緒に平均0.6mの厚い一年氷も運ばれていた。この鉛直に一様な冬季水は,周りの水と混合し,この海域の表層水をより高塩化し東サハリン海流水の性質を失わせる。一方,100～300m深の水は逆に,オホーツク海中層に特徴的な低塩,低温,高酸素の海水に変質される。海洋構造と熱収支解析から,氷縁域によく見られる新生氷帯は,まず厚い海氷が移流され,それが融解することによって潜熱を奪って表面水が冷却される,という事前の条件があった上で作られることが示唆された。
• アルゴス海洋漂流ブイによるオホーツク海と親潮域の循環と潮流特性

  大島 慶一郎, 若土 正暁, 深町 康, 水田 元太 Otsuchi marine science = 東京大学海洋研究所大槌臨海研究センター研究報告 26 (26) 92 -92 2001年03月29日 [査読無し][通常論文]
   

  平成12年度共同利用研究集会「北太平洋北西部とその縁辺海の水塊変動と循環」（2000年8月24日～25日, 研究代表者：岩坂直人）講演要旨
• ブッソル海峡を通りオホーツク海を横切る断面でみた体積・塩分・溶存酸素輸送量収支 1998年8月クロモフ号観測結果から

  河野時広, 水田元太, 大島慶一郎, 深町康, 伊東素代, GLADYSHEV S V, 滝沢隆俊, 若土正暁 日本海洋学会大会講演要旨集 1999 1999年
• MESOSCALE ICE-OCEAN FEATURES IN THE MARGINAL ICE ZONE OFF SYOWA STATION OBSERVED IN NOAA AVHRR IMAGERY

  FUKAMACHI Yasushi, OHSHIMA Kay I., ISHIKAWA Takayuki Proceedings of the NIPR Symposium on Polar Meteorology and Glaciology 11 266 -266 1997年11月 

  Mesoscale ice-ocean features off Syowa Station are examined using NOAA advanced very high resolution radiometer (AVHRR) data during the summers of 1987 and 1988. Visible-band (channel 2) and infrared-band (channel 4) images are used to examine ice and sea surface temperature distributions, respectively. As the melting season progresses, mesoscale ice tongues and eddies are found in the marginal ice zone. The growth of these features is not correlated with the wind field in this area. Comparison between visible and infrared images reveals that the mesoscale ice features are accompanied by corresponding patterns of cold water off the ice edge. Namely, regions of cold water extend off the ice tongues and eddies. This suggests that advection of ice by ocean currents generates the mesoscale features.

特許

• Methods of observing sea ice

  US 7,095,359 B2

共同研究・競争的資金等の研究課題

• 海氷が導く熱・塩・物質のグローバル輸送

  日本学術振興会：科学研究費助成事業

  研究期間 : 2020年08月 -2025年03月 

  代表者 : 大島 慶一郎, 深町 康, 西岡 純, 二橋 創平, 三谷 曜子, 羽角 博康, 田村 岳史, 真壁 竜介, 木村 詞明

   

  高海氷生産域であるフラジルアイス域を検知できるマイクロ波放射計AMSRのアルゴリズムを開発し、南大洋全域で初めてフラジルアイス域のマッピングを行った。フラジルアイス域を検知できたことで、今まで過小評価されていた沿岸ポリニヤでの海氷生産量をより高精度で見積もることができ、従来のアルゴリズムより、20－50％高い海氷生産量が示された。30年あまり継続してあるマイクロ波放射計SSM/I-SSMISデータに対し、薄氷タイプを識別することでより高精度の薄氷厚が推定できるアルゴリズムを開発した。南大洋をベースに開発したこのアルゴリズムは北極海でも適用可能であることも示され、全球に汎用性のあるアルゴリズムであることが示された。この開発により、長期間での全球での沿岸ポリニヤの海氷生産量の見積もりに道が開けた。プロファイリングフロートの溶存酸素量の変動から、初めてオホーツク海の広範囲で正味の生物生産量（純群集生産量）を見積もることに成功し、春の植物プランクトンの大増殖（春季ブルーム）は海氷融解によってもたらされていることを定量的指標をもって明らかにした。さらに、海氷融解時に放出される物質（鉄分）がブルームを誘起していることを示唆し、海氷による物質輸送の重要性を示した。観測としては、2021年3月に小型砕氷船ガリンコ号を傭船し、海氷サンプリングや氷縁での観測を実施し、海氷による物質輸送の観測研究に着手した。この他、CTDタグを購入し、データ通信用のアルゴスシステムに登録するなど、アザラシ、トドによるバイオロギング観測を行う準備を整えた。
• ADCPによる海中浮遊物の識別手法開発と物質循環研究への応用

  日本学術振興会：科学研究費助成事業

  研究期間 : 2020年07月 -2023年03月 

  代表者 : 大島 慶一郎, 深町 康, 伊藤 優人

   

  超音波流速計ADCPの体積後方散乱強度データから、生物(主に動物プランクトン)活動、堆積物の巻き上がり、海中内部で生成される海氷(フラジルアイス)、等の海中浮遊物を検知・識別する手法を開発した。識別手法としては、複素EOF(CEOF)解析とバンドパスフィルタリングを主として用いた。中心周波数24時間のバンドパスフィルタをかけ、CEOF解析を施すことで、動物プランクトンの日周活動を明瞭に抽出する汎用性の高い手法を開発した。この方法では、潮流の強い海域では堆積物巻き上がりも抽出されるが、位相差の違いから両者は識別可能となる。フラジルアイス及び海底堆積物の巻き上がりに関しては、上層(フラジルアイスの場合)、下層(巻き上がりの場合)に重みをつけたCEOF解析、風速(フラジルアイスの場合)・海底流速(巻き上がりの場合)との結合EOF解析等を組み合わせることで、抽出はある程度可能となることもわかった。以上の識別手法を、オホーツク海、北極チュクチ海、南極ケープダンレーポリニヤ域で取得された係留系ADCPデータに適用した。南極ケープダンレー沖沿岸の係留データからは、日が昇らない冬季に動物プランクトンの日周鉛直活動が月の満ち欠けに呼応する1か月周期の変動を示すことを、南極域では初めて明らかにした。また、南極域及びオホーツク海の係留データからは、冬季海氷期は、海氷のない時期とは逆に、沿岸域より沖合域の方が動物プランクトンの日周鉛直活動が活発となることが示された。一方、過去にサンプリングした海氷の粒度粒径分布の解析を継続して行い、フラジルアイスによる堆積物取り込み過程の検討を行った。オホーツク海では2022年2月、砕氷巡視船そうやにより、新たな海氷サンプリングも行った。
• 冬季の海氷厚変動から見た北極海太平洋側海域における夏季の海氷量減少

  文部科学省：科学研究費補助金（基盤研究（B))

  研究期間 : 2019年 -2022年 

  代表者 : 深町 康

   

  北極海の太平洋側海域では夏季の海氷域の減少が近年になって特に顕著に見られているが、その要因は未だに良く解明されていない。その理由の一つは人工衛星データから正確に把握できる海氷の面積に較べて、その厚さの実態把握が不十分なことである。本研究ではこの海域における10 年以上の長期に渡る海氷・海洋の現場観測による海氷厚などのデータと衛星マイクロ波放射計データから見積られる海氷生産量のデータなどを用いて、海氷の力学過程（海氷同士の衝突と重なりによる氷厚の増加）と熱力学過程から決まる冬季の海氷厚分布の実態を明らかにし、それが夏季の海氷分布とどのように関係しているかを調べ、この海氷減少の要因を明らかにする。
• ポリニヤを起点とする熱塩／物質循環 研究課題

  文部科学省：科学研究費補助金（基盤研究（A))

  研究期間 : 2017年 -2019年 

  代表者 : 大島 慶一郎

   

  南極底層水の起源水を生成しているケープダンレーポリニヤにおいて、過去に取得した係留系ADCPの後方散乱強度データから、海中でのフラジルアイスの生成だけでなく、生物活動のシグナルも捉えることにも成功した。最大の発見は、2月後半から3月にかけての海氷（フラジルアイス）生成開始に同期して、最大の生物シグナルが観測されたことである。これはごく最近報告された、フラジル・ブルーミングに相当すると考えられる。第59次南極地域観測隊では、ちょうどこのタイミングで海氷サンプリングを行うことに成功し、今後の解析により、大きな生物基礎生産が生じている可能性のあるフラジル・ブルーミングのメカニズム解明が期待される。また、2018年2月、第59次隊の協力のもと、ポリニヤ内において、海底堆積物の巻き上がりが生ずると推定される海域にADCPと濁度計等を取り付けた係留系を設置することにも成功した。さらに、2018年度実施予定のケープダンレー沖の係留系設置の準備として、係留系に設置される測器の購入とそのテスト・キャリブレーションなども行った。一方、衛星マイクロ波放射計データからフラジルアイスを検知できるアルゴリズムを完成させ、係留系ADCPによる海中フラジルアイス検知ともよく対応することが示された。今後、衛星海氷データと係留系データの組み合わせによる解析から、ポリニヤでの高海氷生産システムや物質循環の理解が深まることが期待される。北極チャクチ海ポリニヤにおいても、2017年8月アラスカ大学と共同して、ADCP・氷厚計・濁度計等からなる3系の係留系を設置することに成功した。また、前年度設置していた2系の係留系の回収にも成功し、ここのポリニヤを起点とする物質循環解明に資するデータを取得できた。オホーツク海に関しては、過去に蓄積されたフロートデータの解析を開始し、中層水等の季節変動を抽出する研究を行った。
• 北極海の海氷変動の鍵を握るアラスカ北部沿岸域での海氷・海洋変動の実態解明

  文部科学省：科学研究費補助金(基盤研究(B))

  研究期間 : 2015年 -2018年 

  代表者 : 深町 康

   

  フィールド観測については、8月に研究分担者の大島らがアラスカ北部に出向き、アラスカ大学フェアバンクス校の研究協力者と共同で、2015年に設置した3系の係留系の回収作業を実施した。また、国際協力によって行われているアラスカ北部沖における船舶観測についても、海洋研究開発機構の「みらい」を含む複数の研究船によって実施された。 アラスカ北部の沿岸域に係留されていた超音波氷厚計の生データから海氷厚の導出処理を終えて昨年度までに整備したアラスカ北部沿岸域における2009年から2015年までの6年分の時系列データを用いて、その経年変動についての解析を行った。その結果として、海氷厚の特徴（平均値、頻度分布など）に大きな経年変動が存在することを示し、その要因がこの海域の風速場に支配される海氷の漂流パターンの変動にあることを明らかにした。 これまでにアラスカ北部沿岸域に設置した係留系から得られた海洋の時系列データ（水温・塩分と海流流速）を周辺海域で得られた同様のデータ、人工衛星搭載のマイクロ波放射計データから推定される海氷厚に気象観測データを合わせて計算される海氷生産量データ、現実的で高解像度の海氷・海洋結合モデルの結果と合わせて解析した。その結果として、この海域における海水特性の変質過程に大きな経年変動が存在し、その要因がこの海域において岸沿いに吹く北東風の変動にあることを明らかにした。この北東風は北極海中層に広く分布する大西洋を起源とする海水の湧昇をもたらすため、太平洋側北極海でありながら、アラスカ北部沿岸域における海水特性の変質には大西洋水の影響が顕著であることも示した。
• 南極海オーバーターニングにおける淡水量変化の量的把握と原因究明

  文部科学省：科学研究費補助金(基盤研究(B))

  研究期間 : 2013年 -2016年 

  代表者 : 青木 茂

   

  地球規模の海洋オーバーターンをになう底層の南極起源の海水は、近年、淡水化しつつあると指摘される。南極大陸沿岸で生まれる海水が全大洋底層の水のもとの一つとなるので、この沿岸海洋の変質の実態を把握して淡水化の原因を探るために、酸素の同位体をつかった特殊なトレーサーを含む観測研究を推進した。オーバーターンの起点となる海域の一つであるロス海沿岸部は淡水化しているが、これは西南極海洋の暖水化と同期していた。もう一つの起点であるアデリーランド沿岸では、海氷生産の減少に加えて氷床融解成分の増加がみられた。これらより、大規模とローカルな氷況変化の両方が淡水含有量に大きな影響を与える可能性が明らかになった。
• 海氷生成とリンクする南極底層水・深層循環の再描像

  文部科学省：科学研究費補助金(基盤研究(A))

  研究期間 : 2013年 -2016年 

  代表者 : 大島 慶一郎

   

  東南極を中心として、沿岸ポリニヤでの高海氷生成による底層水形成の詳細を明らかにした。南大洋第2の海氷生産域であるケープダンレーポリニヤでは、係留系観測等から、海中フラジルアイス生成による高海氷生産過程や、高密度水が混合・変質して底層水に至る過程を明らかにした。第3の海氷生産域であったメルツポリニヤでは、氷河舌の崩壊によって海氷生産量が半減し、底層水生成が大きく減少していることが示された。これら以外に、東南極ではプリッツ湾及びビンセネス湾でも小規模ではあるが高海氷生産による底層水形成が示され、ポリニヤ高海氷生産（正）と棚氷融解（負）の効果の兼ね合いで底層水形成が決まることも示唆された。
• ケープダンレー沖は南極底層水の主要な生成域か?

  文部科学省：科学研究費補助金(基盤研究(B))

  研究期間 : 2011年 -2013年 

  代表者 : 深町 康

   

  2008-09年に南極海インド洋セクターのケープダンレー沖の斜面域で取得した係留観測による海洋の時系列データを、人工衛星による海氷データ、測器を取り付けたアザラシによる海洋データと合わせて、この海域で沿岸ポリニヤでの高い海氷生産に起因したローカルな南極底層水の生成が起こっており、ウェッデル海、ロス海、アデリーランド沖に続く、第4の主要な南極底層水の生成域であること示した。特に、この海域が他の3つの生成域とは異なり、広い大陸棚、棚氷、大きな窪地の全てが存在しないにも関わらず、高い海氷生産のみによって主要な生成域となっていることは特筆に値する。
• 超音波ドップラー流速計を用いた海氷の厚さの計測手法の開発

  文部科学省：学術研究助成基金助成金(挑戦的萌芽研究)

  研究期間 : 2011年 -2013年 

  代表者 : 深町 康

   

  一般に、海氷厚の係留観測には特殊な測器である超音波氷厚計が用いられる。海洋観測に広く用いられている超音波ドップラー流速計を用いた海氷厚の計測手法の開発を行うために、アラスカ北部の沖合で、これらの両方の測器を含む係留系による観測を実施した。3年間に延べ4箇所で両方の測器で良好なデータを取得することに成功し、一部のデータについて超音波氷厚計の生データから海氷厚を算出した。 本研究の観測で取得された海氷・海洋のデータを用いて、沿岸定着氷の崩壊、ポリニヤにおける過冷却水とフラジルアイスの生成、電磁誘導センサーによる海氷厚計測とレーダーによる海氷漂流速度の計測との比較研究についての成果をまとめた。
• 国際観測ネットワークによる南極底層水淡水化の量的把握と氷河融解の影響検証

  文部科学省：科学研究費補助金(基盤研究(B))

  研究期間 : 2009年 -2012年 

  代表者 : 青木 茂, 深町 康

   

  本研究は、酸素安定同位体比測定という新しい手法を標準化した国際共同海洋観測ネットワークによりオーストラリア-南極海盆における南極底層水のここ20年間の淡水化の全体像を把握し、人工衛星や数値実験の結果とも組み合わせてその原因を明らかにすることを目的としている。本年度は、同海盆において低塩化(淡水化)が顕著に報告されている源流域・分岐域・西岸境界域での同期観測を日本とオーストラリアが共同で実施し、低塩化傾向がさらに進行していることが確認された。また同観測において、日豪あわせて約1800個の酸素同位体比用サンプルを取得した。質量分析計による酸素同位体比の継続的な分析をすすめ、南極表層水に氷山融解の影響が特定できることを示した。また、1990年代のWHP観測と2000年代に実施された観測との比較から、本海盆での淡水化率は25GGt/yr程度と見積もられた。これはロス海陸棚域で観測されている淡水化率と同程度にのぼる。水温・塩分変化に基づく評価から、この変化の原因の一つとして、幾つかの仮定の元で、ロス海から流入する底層水の低塩化が大きな割合を占める可能性が示された。もう一つの可能性として、底層水の母海水のひとつであるアデリー海谷における陸棚高密度水の変質が考えられる。陸棚水に対する氷床融解や海氷生産の時間的な変化による変質の可能性を調べるため、メルツ氷河の変動の実態を調べた。人工衛星画像...
• 海氷生産量のグローバルマッピングとモニタリング構築

  文部科学省：科学研究費補助金(基盤研究(S))

  研究期間 : 2008年 -2012年 

  代表者 : 大島 慶一郎, 江淵 直人, 青木 茂, 深町 康, 豊田 威信, 北出 裕二郎

   

  海洋の大規模な中深層循環は極域・海氷域から重い水が沈み込み、それが徐々に湧き上がってくるという密度(熱塩)循環である。海氷生成の際にはき出される高塩分水が重い水の生成源になっている。本研究の目的は、海洋中深層循環及びその変動を決めうる重要な因子である海氷生産量を、現場観測に基づいて衛星データ等から見積もるアルゴリズムを開発し、そのグローバルマッピングを行うことである。さらに海氷生産量と中深層水形成の関係をその変動を含めて理解することもめざす。
• 南極沿岸域における海氷生産量とそれに伴う南極底層水流量の直接的評価

  文部科学省：科学研究費補助金(基盤研究(C))

  研究期間 : 2008年 -2010年 

  代表者 : 深町 康

   

  南極底層水の流出経路であるケルゲレン海台東側斜面域における係留観測データから、この海域における赤道向きの流量がウェッデル海からの流量に匹敵する海洋大循環の重要な割合を占めるものであることを明らかにした。また、海氷生産が盛んなケープダンレーポリニヤ周辺の係留観測から、この海域においてローカルに南極底層水が生成されていることを確かめた。更に、ケープダンレーポリニヤでの海氷厚の係留観測に成功し、南極海の沿岸ポリニヤ内では初となる高精度のデータを取得した。
• 氷厚の現場観測データを用いたオホーツク海における海氷生産量の直接的評価

  文部科学省：科学研究費補助金(基盤研究(C))

  研究期間 : 2005年 -2007年 

  代表者 : 深町 康, 木村 詞明

   

  北海道沿岸域の湧別沖で1999-2001年の冬季に得られた氷厚の係留観測データの解析結果から、draft(水面下の海氷厚)の平均値が0.60mであること、力学的な変形を受けた海氷の割合が80%と非常に高いことなどを明らかにし、これらの結果をFukamachi et al.(2006, Journal of Geophysical Research)にまとめて発表した。また,国立環境研のセジメントトラップ観測と共同で、2005-06年に紋別沖で実施した係留観測の結果から、生物起源や岩石起源の沈降物質の質や量が海氷の有無とともに変動していることを示し、これらの結果をHiwatari et al.(2008, Polar Science)にまとめて発表した。サハリン北部沿岸域で2002-03年の冬季に得られた氷厚データの解析結果から、draftの平均値は1.05mで、北海道沿岸域に較べて顕著に大きいこと、0.2m程度の薄い海氷と数mを超える厚い海氷が卓越する時期が有り、それぞれ沖向きと岸向きの漂流速度に対応していること、薄い海氷の時期には海水中の塩分の上昇が見られ、ポテンシャル密度が26.7を超える高密度陸棚水が存在すること、観測された塩分の上昇が、大気と海氷・海洋間の熱収支から計算される海氷生産量から求められるものでよく説明されることなどについて明らかにし、これらの結果をFuka...
• オホーツク海における、海水・海氷・油の流動予測システムの開発

  文部科学省：科学研究費補助金(基盤研究(B))

  研究期間 : 2005年 -2007年 

  代表者 : 大島 慶一郎, 若土 正曉, 江淵 直人, 三寺 史夫, 深町 康

   

  海水・海氷・油の流動予測の基盤となる3次元海洋モデルを開発・高精度化した。最終的には、分解能1/12度で、日本海と太平洋の海水交換も含み、日々の風応力と月平均の海面熱フラックスによって駆動されるモデルを開発した。係留系及び海洋レーダーより取得した測流データとモデルとの比較・検討により、東樺太海流・宗谷暖流に関しては非常に再現性のよいモデルを開発することができた。このモデルに粒子追跡法を取り入れて、サハリン油田起源の海水の漂流拡散を調べた。水平拡散の効果は、Markov-chain modelを仮定したランダムウォークを用いて取り入れた。表面下15mでは粒子の漂流はほとんど海流(東樺太海流)で決まり、粒子は東樺太海流に乗って樺太東を南下しあまり拡散せずに北海道沖に達する。表層(0m)では、風による漂流効果も受けるので、サハリン沖の粒子の漂流は卓越風の風向に大きく依存する。沖向き成分の風が強い年は、表面の粒子は東樺太海流の主流からはずれ、北海道沖まで到達する粒子の割合は大きく減じる。アムール川起源の汚染物質の流動予測も同様に行い、東樺太海流による輸送効果の重要性が示された。2006年2・3月に起こった知床沿岸への油まみれ海鳥の漂着問題に、後方粒子追跡実験を適用し、死骸は11-12月のサハリン沿岸から流れてきた可能性が高いことを示した。潮流による拡散効果を正しく評価するために、主要...
• 南極海インド洋セクターにおける海洋循環と南北熱塩輸送の量的把握

  文部科学省：科学研究費補助金(基盤研究(B))

  研究期間 : 2005年 -2007年 

  代表者 : 若土 正暁, 木村 詞明, 大島 慶一郎, 青木 茂, 深町 康, 牛尾 収輝

   

  本研究の最重要課題は、南極海インド洋セクターで生成する南極底層水の北上流の季節変動を初めて捉えることに成功した現地観測データを解析することにある。我々は、ウエッデル海やロス海とともに南極底層水の主要な生成域の一つであり、これまで南北輸送流量のデータの全く無いアデリーランド沖をターゲットとして、冬季沿岸ポリニア域で生成する南極底層水が陸棚斜面を下降し、やがて西岸境界流としてケルゲレン海台東岸沖の海底近くを北上する海流量の季節変動を直接捉えるための流速計を中心とする係留観測を実施した。これは豪州CSIROとの共同研究として実施したものであり、2003年2月から2005年1月までの2年間にわたる、合計8観測点での流向、流速、水温、塩分、溶存酸素量のデータ取得に初めて成功した。極めて貴重な、そして膨大なデータの解析を現在精力的に進めている。これまでの解析から、特徴的なのは、どこの観測点でも流向が一様であり、ケルゲレン海台東岸沖斜面域では北西流が、遥か沖合の深海域では全く逆向きの南東流が卓越していることである。つまり、この海域では、ケルゲレン海台東岸沖の南極底層流の西岸境界流としての北上流と、その沖合での再循環による南下流の二つの卓越する循環系から構成されていることが分かった。本研究ではまた、南極底層水生成域である沿岸ポリニア域で形成する海氷の氷厚分布を人工衛星データから検出して、熱収...
• オホーツク海における環堺変動と海氷気候及び動態の機構解析

  文部科学省：科学研究費補助金(基盤研究(B))

  研究期間 : 2003年 -2005年 

  代表者 : 白澤 邦男, 高橋 正征, 深町 康, 兒玉 裕二, 河村 俊行, 池田 元美, 舘山 一孝

   

  (1)サハリン北東部の気象、海洋、海氷の現場観測:通年の気象、海象、海氷観測を実施し、季節内変動、年々変動を調べ、海氷成長モデルの検証を行った。電磁誘導式氷厚計による海氷厚の計測、係留型氷厚計とADCP(流速プロファイラー)による海氷厚と流氷漂流速度の季節内変動を調べた。(2)北海道オホーック海沿岸域での現場観測及びリモートセンシングによる気象、海洋、海氷観測:巡視船「そうや」に電磁誘導式氷厚計を搭載し南部オホーツク海の広域氷厚分布の計測、ブイによる流氷漂流動態の観測を実施した。サロマ湖では、海氷成長モデル検証のための気象、海洋、海氷の現場観測、海氷生態系過程を把握するためにアイスアルジーの分布や発達過程の実験観測を行った。係留型氷厚計、ADCP、セジメントトラップを係留し、海氷厚、流氷漂流速度の連続観測、流氷下の沈降物質と流氷分布との関係を調べた。流氷レーダーによる流氷分布や移動速度の観測、宗谷海峡とオホーツク海沿岸域に設置した短波海洋レーダーによる表面海流速度の連続観測を行った。(3)オホーツク海とバルト海の海氷気候、海洋環境の比較研究:季節海氷域であるバルト海において、気象、海氷、海洋環境、海洋生態系の現場観測を行い、季節内変動、年々変動を調べ、オホーツク海の海氷気候や海洋環境との比較研究を行った。(4)南極海、北極海の海氷厚計測:船舶搭載型電磁誘導式氷厚計を用いて、南...
• 海氷の厚さの係留観測データを用いたオホーツク海における海氷量の評価

  文部科学省：科学研究費補助金(奨励研究(A))

  研究期間 : 2000年 -2001年 

  代表者 : 深町 康

   

  1.係留観測データの解析2001年の冬季に、過去2年間と同じように、北海道沿岸域湧別沖6マイルの地点で得られたIce Profiling Sonar(IPS)のデータの解析を行った。この年は、オホーツク海全体における最大海氷面積が1979年以来の最大であったことからも推測されるように、1月上旬から係留観測点において海氷が観測されていたが、氷厚については、過去2年間に見られたような極端に大きいice keelはあまり見られなかった。この理由としては、海氷の密接度が高かったために、raftingやridgingのような変形プロセスが起きにくかったことが考えられる。2001年を含めたこれまでの3年間の氷厚データの特徴は、各年について大きく異なっている。このことは、北海道沿岸域に存在する海氷は、海氷面積のみならず、氷厚についても、大きな年々変動があることを示唆しており、海氷量の見積もりに対しての氷厚の重要性をも示している。2.更なる観測の実施2001年11月には、過去3年間と同様に、湧別沖にIPSとAcoustic Doppler Current Profilerを設置しており、近日中に回収の予定である。また、海氷域における氷厚観測の可能性を広げるために、自律走行型海中ロボットAUV(Autonomous Underwater Vehicle)にIPSを搭載して、紋別港周辺の海域にお...
• 季節海氷域における融解期の海氷・海洋結合システム

  文部科学省：科学研究費補助金(基盤研究(C))

  研究期間 : 1997年 -1999年 

  代表者 : 大島 慶一郎, 浮田 甚郎, 深町 康

   

  夏季南極海海氷域の熱収支から、大気からの熱のインプットはアルベドの違いから海氷面より開水面からのほうがずっと大きく、海氷融解は開水面からの熱が海氷を側面と底面から融かしていく過程が重要であることが定量的に確かめられた。海氷の融解が大気から開水面に入る熱によってのみで行われると成り立つ、(海氷融解率)=(開水面の割合)*(大気からの熱的外力)という単純な関係が、現実のデータ(マイクロ波放射計による海氷密接度データ)からも示唆された。人工衛星による海氷データを用いて調べたところ、ほとんどの年で融解最盛期の12月と結氷期の4月における海氷密接度のアノマリーの空間分布はよく一致していた。12月は海氷分布の年々変動が最も大きい月でもあるので、この時期に大気から海洋上層中に与えられる熱は、年により大きく異なることになる。解析の結果、融解期における海氷の多少が、海洋上層へ与えられる熱の多寡を生み、それが海に記憶されて、海氷が一度消滅した後、結氷期にも反映されることが示唆された。海氷の融解は開水面から海洋混合層に入った熱によってのみ起こるとする簡略な海氷・海洋結合モデルを提出した。モデルから、海氷密接度と混合層の水温との関係は、あるカーブに収束することが示され、昭和基地沖やロス海での観測をよく説明している。また、このモデルは南極の子午面方向の海氷後退をある程度説明しえ、第0近似的には海氷融解...
• 第3世代の化学トレーサーを用いた高緯度海洋における水塊混合の履歴の解析

  文部科学省：科学研究費補助金(基盤研究(B))

  研究期間 : 1997年 -1998年 

  代表者 : 中塚 武, 深町 康, 大島 慶一郎

   

  本科研費を用いた研究は、主に次の2つの部分からなる。一つは、硝酸塩の窒素同位体比を用いた海洋表層における生物活動と水塊混合の履歴の解析であり、もう一つは、栄養塩の精密濃度測定に基づく中・深層水の移流混合過程の解析である。前者には、主にべーリング海やアラスカ湾で日本・カナダ間の往復貨物船により周年的に採取された表層水試料を用い、後者には、オホーツク海南部海盆域でロシア船を使って行われたCTD/RMS観測の試料を用いた。当科研費の大部分は、それぞれ窒素同位体比、栄養塩濃度の測定用の真空ラインの製作、栄養塩自動分析計の購入に充てられた。硝酸塩の窒素同位体比を用いた表層水の混合過程の解析では、硝酸塩の濃度-同位体比プロットにより、ベーリング海においては、アラスカ湾中央部よりも夏季の表層水の鉛直混合が活発である可能性が示唆された。栄養塩の精密測定による中・深層水の移流混合過程の解析では、特に硝酸塩とリン酸塩の濃度を用いた新たな化学量であるN^*(=([NO_<3->]-16・[PO_4^<3->]+2.9)・0.87)が、水塊の起源と混合過程の追跡に極めて有効であることを見いだした。このN^*は、通常は海中では変化せず一部の海域や海底泥中のみでおこる脱窒や窒素固定によってそれぞれ減少・増加する「準保存量」である。このN^*の分布をオホーツク海南部全体で詳細に求めたところ、海底・大陸斜面...
• 衛星と現場観測による、オホーツク海の海氷変動とそれに伴なう熱塩収支過程の研究

  文部科学省：科学研究費補助金(重点領域研究)

  研究期間 : 1997年 -1997年 

  代表者 : 大島 慶一郎, 水田 元太, 深町 康, 竹内 謙介, 若土 正曉

   

  オホーツク海冬季の現場での海氷・海洋データは今までほとんど得られていなかった。1996,1997,1998年2月の3年にわたって海上保安庁の砕氷船「そうや」により、オホーツク海南西部において、海氷の諸量及び海洋構造の観測を行った。海氷の厚さは1996,1998年は平均20〜30cm程度であったが、1997年は60cmあり、年によって大きく異なることがわかった。従って、衛星データから得られる密接度のデータから海氷の量的な評価を行うことは大きな問題がある。また、この氷厚の違いが何によるのかは今後の興味深い課題である。海氷アルベド(日射に対する反射率)は1996,1997年の観測から、オホーツク海では氷状によらずほぼ0.6〜0.65程度であることがわかった。1997年2月の海氷域での海氷観測データから以下のことが明らかになった。オホーツク海では冬季、結氷温度で一様な海洋混合層が300m以上に及ぶ場合がある。これは、海氷生成による鉛直対流だけでなく、南風による岸でのエクマン収束のようなmechanicalな効果によることも示唆される。このような厚い混合層を持つ水塊は東カラフト海流として海底斜面に沿ってカラフト沿岸沿いを南下し、それに伴って厚い海氷も南へ運ばれる。移流された海氷の一部は風で周辺の暖水域へ運ばれ、初めはそこで融解され表層を低塩化するが潜熱を奪うことによって、やがてそこを結...
• 南極ポリニアの形成機構の研究

  文部科学省：科学研究費補助金(一般研究(B), 基盤研究(B))

  研究期間 : 1995年 -1997年 

  代表者 : 若土 正暁, 日比谷 紀之, 深町 康, 大島 慶一郎, 河村 俊行

   

  ポリニヤ(Polynya)とは、広大な海氷原の内部(外洋ポリニヤ)や沿岸付近(沿岸ポリニヤ)に定常的に依存する大規模な開水面或いは疎氷域のことをいう。そこでは、大気と海洋の間で熱や各種ガスの交換が活発に行われる。厳冬期になると本来なら海氷で広く覆われてしまうはずの極域海洋において、何故特定の海域だけに開水面が形成し、そのまま維持されるのか、またそれらポリニヤが大気や海洋に果たしている役割は何か、という問題に対する理解を深める事が本研究の目的である。我々は、研究海域として南極昭和基地周辺とオーストラリア南方の南極沿岸域(アデリーランド沖)を取り上げた。前者では、ポリニヤの成因として海洋よりも大気の影響の方が大きいこと、それも大陸からの斜面下降風(カタバ風)野影響を強く受けるところと、もっと広くシノプテイックな大気場が支配的なところと場所によって異なる事がわかった(Ishikawa et al.,1996)。一方、後者のアデリーランド沖では、1995年1月と1996年1月の2回の海洋観測とその間(1995年1月から1996年3月まで)の大陸棚斜面での流速計係留観測を行った。この海域は、南極周辺で海氷密接度の最も低いところとして、よく知られている。我々の観測結果から、以下の事が明らかになった。(1)底層付近に低温、低塩、高酸素、低珪素、高フロンの性質をもつ水塊が2年とも存在した。こ...
• 海氷消長過程における大気-海氷-海洋-生態系システムモデル化のため実験研究

  文部科学省：科学研究費補助金(一般研究(B), 基盤研究(B))

  研究期間 : 1995年 -1997年 

  代表者 : 白澤 邦男, 深町 康, 田口 哲, 児玉 裕二, 石川 信敬, 青田 昌秋, 河村 俊行

   

  冬季に海氷が生成され発達する北海道のサロマ湖を、氷縁域、薄い海氷域のモデル実験フィールドとして、海氷が生成する12月から融解が始まる3月まで現場実験観測を集中的に実施した。1997年12月から1998年3月の冬は3箇年の研究計画の3年度であり、初年度、2年度にできなかった実験観測を集中的に実施した。またモデル作成に必要な基礎データを収集した。(1)海氷の生成から融解に至る過程での大気-海氷間の気象パラメータの収集、(2)海氷消長過程における海氷内部構造、特にブライン・チャンネルを中心にした物理構造の変遷、温度センサーによる海氷中、海氷下海洋境界層の温度分布の季節変動の測定、照度センサーによる海氷上、中、下の光環境の季節変動の測定、(3)温度・塩分センサー付3次元電磁流速計を繋留しての海氷生成前から融解後までの海氷消長過程における海洋構造の季節変動、海氷-海洋間の運動量、熱、塩フラックスの交換過程の把握、(4)海氷の消長とブラインの排出機構、(5)アイス・アルジ-の分布や離脱量の消長とその生物・化学組成の把握、(6)セジメント・トラップを用いてのアイス・アルジ-、動物プランクトン、沈降粒子物質フラックスの日周、潮汐、季節変化を把握するための現場実験観測を行なった。今冬のサロマ湖海氷上の現場実験観測は修了したが、データ解析は現在進行中である。また、セジメント・トラップと3次元電磁...
• 衛星と現場観測による、オホーツク海の海氷変動とそれに伴なう熱塩収支過程

  文部科学省：科学研究費補助金(重点領域研究)

  研究期間 : 1996年 -1996年 

  代表者 : 大島 慶一郎, 深町 康, 河村 俊行, 若土 正曉

   

  オホーツク海では冬季海氷が覆われる時期での海氷及び海洋の観測は過去にほとんど行なわれていない。1996年2月と1997年2月に海上保安庁の砕氷船「そうや」により、オホーツク海南西部において海氷域での海氷・海洋観測を行なった。特に海氷に関しては今まで計られていない海氷の厚さ、アルベド(日射に対する反射率)の観測を行った。海氷の厚さは1996年では5〜30cmで平均20cm程度、1997年では20〜80cmで両年で大きな違いがあった。今後、この違いは何によるのかを衛星データと組み合わせた解析を行なう予定である。オホーツク海の海氷のアルベドは平均して0.59と推定された。ただし、ダ-クニラスのアルベドは約0.1という値となり、この低い値はニラスの結晶構造によることも示唆された。海洋構造の観測から、冬季のオホーツク海南西域では北方より水が流れていること、またその冬季の鉛直混合対流は300m以上にも及ぶことが観測された。また、氷縁域ではまず海氷が移流され融解して海水が低温低塩化し、それが現場結氷を生じさせる状況をつくっていることが明らかになった。マイクロ波放射計データ(DMSP SSM/I)から海氷の密接度だけでなく海氷の種類(Ice Type)の情報を用いて、海氷の結氷域に注目することによって海氷の特徴的な変動過程を調べた。氷縁域での広範囲に及ぶ結氷は、大気場の擾乱により海氷域が急速...
• 氷縁域におけるメソスケール渦の研究

  文部科学省：科学研究費補助金(奨励研究(A))

  研究期間 : 1995年 -1995年 

  代表者 : 深町 康

   

  夏季の氷縁域において特徴的に見られるメソスケール渦などの中規模現象の形成機構を調べるために、力学・熱力学の両過程を含む水平2次元の海氷・海洋結合モデルを作成した。このモデルにおいて南極海で観測されたパラメーターを用い、外力としては熱力学過程の重要性を理解するために大気からの熱フラックスのみを与えて計算を行なった。大気からの熱フラックスに対する応答として、氷縁付近で海氷の融解が最も盛んとなり、塩分フロントが形成された。この塩分フロントと地衡流バランスで釣り合っている氷縁に沿う流れは、その流速が増加するにつれて蛇行するようになった。この蛇行は、海氷域の低温・低塩水と開水域の高温・高塩水の交換を促進すると共に、海氷を開水域に移流し舌状の海氷分布を形成した。結果として、蛇行の成長につれて、海氷の融解が更に促進されることとなった。この蛇行の形成機構を解明するために、海洋モデルの線形不安定解析を行なったところ、水平密度フロントに起因する傾圧不安定がその成因であることが明らかになった。氷縁域で見られる様々なメソスケール現象の形成には、風による力学的な効果が重要な役割を果たしていることは間違い無い。しかしながら、この研究によって、海氷が融解する夏季においては、熱力学的な効果も重要な役割を果たしていることが示された。現時点では、南極海等で夏季に海氷の分布によって可視化されるメソスケール渦そのも...
• 極域海洋における氷山融解過程の研究

  文部科学省：科学研究費補助金(重点領域研究)

  研究期間 : 1993年 -1993年 

  代表者 : 若土 正暁, 若土 正曉, 長島 秀樹, 深町 康, 大島 慶一郎

   

  本研究では、時間的にも空間的にも最もグローバルな水循環系の一部を占める極域海洋における氷山融解過程を明らかにするために現場観測と水槽実験を試みた。(1)現場観測;研究分担者大島は第32次日本南極地域観測隊(1990〜1992)に参加し、ACR(南極気候研究)の一貫として、昭和基地周辺の海洋・海氷観測を実施した。そのうち、リュツォ・ホルム湾の定着氷に捕捉された氷山近傍で実施したCTD観測において、水温・塩分の鉛直プロファイルがステップ(階段)構造を示していることを見い出した(Ohshima et al.,1994)。これらT,Sのステップ構造は氷山が喫水している範囲内の深さにおいてのみ見られた。典型的なステップの厚さは20〜30m、その水温差、塩分差はそれぞれ0.05℃、0.05〜0.10%_0であった。このステップ構造は、海洋に対する氷山の何らかの影響を示しており、塩分成層した海洋中での氷山の側壁融解過程に伴って誘起された可能性がある。氷山に限らず、棚氷や海氷などの融解は、夏季の極域海洋における支配的な海洋現象として、その物理過程を調べることは重要である。(2)水槽実験:海洋中における氷山融解過程の研究は、今までにも極端に単純化した形の水槽実験が試みられている。それらは、密度成層か密度一様か、側壁融解か底面融解かに大きく分類される。そのうち、本研究では、今まで全くなされていな...
• 日本海底層水形成に関わる間宮海峡の海洋・海氷研究

  文部科学省：科学研究費補助金(一般研究(C))

  研究期間 : 1993年 -1993年 

  代表者 : 若土 正暁, 若土 正曉, 深町 康, 大島 慶一郎

   

  本研究の目的は、海象データの解析、人工衛星からの画像データによる氷状観測、さらには数値実験などによって、日本海底層水の形成機構を明らかにすることである。特に今回初めて得られたヨーロッパの地球資源衛星(ERS-1)からの合成開口レーダ(SAR)画像をはじめ、AVHRRの可視・赤外画像などを解析することによって、日本海底層水形成に本質的な役割を果たしていると考えられている、間宮海峡やシベリヤ沿岸沖の海氷生成過程についての定量的な情報を得る。幸いにも、今回解析したデータの中には、明らかに気象条件の異なる場合(強風と微風)が含まれていたので、両者を比較検討することによって、以下のような風による海氷過程の違いを観測することが出来た。まず、北風の強い時には、シベリヤ沿岸沖に形成した沿岸ポリニヤ域で、急速なフラジルアイスの生成と風による風下への吹き流しが大規模に起こっていることが観測された。一方、風がほとんど無かった時には、漂流ベクトルを求めた画像解析によって、氷が5〜15km/dayの速度で北向きに移動していることが観測された。この微風条件下にもかかわらず北向きの漂流は、連続性から、その補償流として、やや深い層を南向きに流れるプリュームが存在してるはずであることを示唆している。このプリュームは海氷生成にともなって排出されるブライン(高塩分水)によってもたらされていると考えられる。2層モデ...

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