基本情報

所属

• 北方生物圏フィールド科学センター

職名

• 准教授

学位

• 博士 (環境科学)（2008年03月 北海道大学）

ホームページURL

https://sites.google.com/view/daikinomura/home

科研費研究者番号

• 70550739

J-Global ID

• 201101097953619342

研究キーワード

• 海氷   二酸化炭素   気体交換   融解水   海洋   極域   

研究分野

• 環境・農学 / 環境動態解析

担当教育組織

•  学士課程　水産学部
•  修士課程　水産科学院
•  博士課程　水産科学院

職歴

• 2024年01月 - 現在 SOLAS SSC member
• 2021年09月 - 現在 SCOR WG163 Full member
• 2021年04月 - 現在 国立極地研究所 客員准教授
• 2020年04月 - 現在 北海道大学 北方生物圏フィールド科学センター 准教授
• 2018年01月 - 現在 CATCH SSC member
• 2016年04月 - 現在 北海道大学北極域研究センター 兼任
• 2016年06月 - 2023年12月 SCOR WG152 Co-chair
• 2015年10月 - 2020年03月 北海道大学大学院水産科学研究院 助教
• 2015年04月 - 2015年09月 北海道大学低温科学研究所 非常勤研究員
• 2013年04月 - 2015年03月 日本学術振興会 特別研究員PD（北海道大学低温科学研究所）
• 2012年04月 - 2013年03月 日本学術振興会 特別研究員PD（ノルウェー極地研究所）
• 2011年04月 - 2012年03月 日本学術振興会 海外特別研究員（ノルウェー極地研究所）
• 2009年04月 - 2011年03月 国立極地研究所 特任研究員
• 2008年04月 - 2009年03月 日本学術振興会 特別研究員PD（北海道大学低温科学研究所） （DC2採用後PDに変更）
• 2007年04月 - 2008年03月 日本学術振興会 特別研究員DC2（北海道大学大学院環境科学院）

研究活動情報

論文

• Classification of optical water groups in the subarctic Pacific and adjacent seas using satellite-derived light absorption spectra of chromophoric dissolved organic matter

  Joji Oida, Toru Hirawake, Youhei Yamashita, Hiroto Abe, Jun Nishioka, Hisatomo Waga, Daiki Nomura, Shigeho Kakehi

  Deep Sea Research Part I: Oceanographic Research Papers 104313 - 104313 2024年04月 [査読有り]
  
• Oceanographic factors determining the distribution of nutrients and primary production in the subpolar Southern Ocean

  Manami Tozawa, Daiki Nomura, Kaihe Yamazaki, Masaaki Kiuchi, Daisuke Hirano, Shigeru Aoki, Hiroko Sasaki, Hiroto Murase

  Progress in Oceanography 103266 - 103266 2024年04月 [査読有り]
  
• Isotopic signatures of snow, sea ice, and surface seawater in the central Arctic Ocean during the MOSAiC expedition

  Moein Mella, Camilla F. Brunello, Martin Werner, Dorothea Bauch, Ellen Damm, Michael Angelopoulos, Daiki Nomura, Jeffrey M. Welker, Martin Schneebeli, Mats A. Granskog, Maria Hoerhold, Amy R. Macfarlane, Stefanie Arnd, Hanno Meyer

  Elem Sci Anth 12 1 2024年02月22日 [査読有り][通常論文]
   

  The Arctic Ocean is an exceptional environment where hydrosphere, cryosphere, and atmosphere are closely interconnected. Changes in sea-ice extent and thickness affect ocean currents, as well as moisture and heat exchange with the atmosphere. Energy and water fluxes impact the formation and melting of sea ice and snow cover. Here, we present a comprehensive statistical analysis of the stable water isotopes of various hydrological components in the central Arctic obtained during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition in 2019–2020, including the understudied Arctic winter. Our dataset comprises >2200 water, snow, and ice samples. Snow had the most depleted and variable isotopic composition, with δ18O (–16.3‰) increasing consistently from surface (–22.5‰) to bottom (–9.7‰) of the snowpack, suggesting that snow metamorphism and wind-induced transport may overprint the original precipitation isotope values. In the Arctic Ocean, isotopes also help to distinguish between different sea-ice types, and whether there is a meteoric contribution. The isotopic composition and salinity of surface seawater indicated relative contributions from different freshwater sources: lower δ18O (approximately –3.0‰) and salinities were observed near the eastern Siberian shelves and towards the center of the Transpolar Drift due to river discharge. Higher δ18O (approximately –1.5‰) and salinities were associated with an Atlantic source when the RV Polarstern crossed the Gakkel Ridge into the Nansen Basin. These changes were driven mainly by the shifts within the Transpolar Drift that carried the Polarstern across the Arctic Ocean. Our isotopic analysis highlights the importance of investigating isotope fractionation effects, for example, during sea-ice formation and melting. A systematic full-year sampling for water isotopes from different components strengthens our understanding of the Arctic water cycle and provides crucial insights into the interaction between atmosphere, sea ice, and ocean and their spatio-temporal variations during MOSAiC.
• Comparisons of different sample air-drying systems for carbon dioxide flux measurements based on eddy covariance in cold environments

  Taichi NOSHIRO, Daiki NOMURA, Fumiyoshi KONDO, Keisuke ONO, Brent ELSE, Hiroki IKAWA

  Journal of Agricultural Meteorology 80 1 22 - 28 2024年01月10日 [査読有り]
  
• Size-fractionated phytoplankton biomass and primary production in the eastern Indian sector of the Southern Ocean in the austral summer 2018/2019

  Akihiro Shiomoto, Hiroko Sasaki, Daiki Nomura

  Progress in Oceanography 218 103119 - 103119 2023年11月 [査読有り]
  
• Responses of diatom assemblages and life cycle to sea ice variation in the eastern Indian sector of the Southern Ocean during austral summer 2018/2019

  Kohei Matsuno, Kohei Sumiya, Manami Tozawa, Daiki Nomura, Hiroko Sasaki, Atsushi Yamaguchi, Hiroto Murase

  Progress in Oceanography 218 103117 - 103117 2023年11月 [査読有り]
  
• Polar oceans and sea ice in a changing climate

  Megan D. Willis, Delphine Lannuzel, Brent Else, Hélène Ango, Karley Campbell, Odile Crabeck, Bruno Delille, Hakase Hayashida, Martine Lizotte, Brice Loose, Klaus M. Meiners, Lisa Miller, Sebastien Moreau, Daiki Nomura, John Prytherch, Julia Schmale, Nadja Steiner, Letizia Tedesco, Jennie Thomas

  Elem Sci Anth 11 1 2023年10月18日 [査読有り]
   

  Polar oceans and sea ice cover 15% of the Earth’s ocean surface, and the environment is changing rapidly at both poles. Improving knowledge on the interactions between the atmospheric and oceanic realms in the polar regions, a Surface Ocean–Lower Atmosphere Study (SOLAS) project key focus, is essential to understanding the Earth system in the context of climate change. However, our ability to monitor the pace and magnitude of changes in the polar regions and evaluate their impacts for the rest of the globe is limited by both remoteness and sea-ice coverage. Sea ice not only supports biological activity and mediates gas and aerosol exchange but can also hinder some in-situ and remote sensing observations. While satellite remote sensing provides the baseline climate record for sea-ice properties and extent, these techniques cannot provide key variables within and below sea ice. Recent robotics, modeling, and in-situ measurement advances have opened new possibilities for understanding the ocean–sea ice–atmosphere system, but critical knowledge gaps remain. Seasonal and long-term observations are clearly lacking across all variables and phases. Observational and modeling efforts across the sea-ice, ocean, and atmospheric domains must be better linked to achieve a system-level understanding of polar ocean and sea-ice environments. As polar oceans are warming and sea ice is becoming thinner and more ephemeral than before, dramatic changes over a suite of physicochemical and biogeochemical processes are expected, if not already underway. These changes in sea-ice and ocean conditions will affect atmospheric processes by modifying the production of aerosols, aerosol precursors, reactive halogens and oxidants, and the exchange of greenhouse gases. Quantifying which processes will be enhanced or reduced by climate change calls for tailored monitoring programs for high-latitude ocean environments. Open questions in this coupled system will be best resolved by leveraging ongoing international and multidisciplinary programs, such as efforts led by SOLAS, to link research across the ocean–sea ice–atmosphere interface.
• Macronutrient biogeochemistry in Antarctic land-fast sea ice: Insights from a circumpolar data compilation

  Sian F. Henley, Stefano Cozzi, François Fripia, Delphine Lannuzel, Daiki Nomura, David N. Thomas, Klaus M. Meiners, Martin Vancoppenolle, Kevin Arrigo, Jacqueline Stefels, Maria van Leeuwe, Sebastien Moreau, Elizabeth M. Jones, Agneta Fransson, Melissa Chierici, Bruno Delille

  Marine Chemistry 104324 - 104324 2023年10月 [査読有り]
  
• Thin and transient meltwater layers and false bottoms in the Arctic sea ice pack—Recent insights on these historically overlooked features

  Madison M. Smith, Hélène Ango, Emelia J. Chamberlain, Elise S. Droste, Salar Karam, Morven Muilwijk, Alison L. Webb, Stephen D. Archer, Ivo Beck, Byron W. Blomquis, Jeff Bowman, Matthew Boyer, Deborah Bozzato, Melissa Chierici, Jessie Creamean, Alessandra D’Angelo, Bruno Delille, Ilker Fer, Allison A. Fong, Agneta Fransson, Niels Fuchs, Jessie Gardner, Mats A. Granskog, Clara J. M. Hoppe, Mario Hoppema, Mario Hoppmann, Thomas Mock, Sofia Muller, Oliver Müller, Marcel Nicolaus, Daiki Nomura, Tuukka Petäjä, Evgenii Salganik, Julia Schmale, Katrin Schmid, Kirstin M. Schulz, Matthew D. Shupe, Jacqueline Stefels, Linda Thielke, Sandra Tippenhauer, Adam Ulfsbo, Maria van Leeuwe, Melinda Webster, Masaki Yoshimura, Liyang Zhan

  Elem Sci Anth 11 1 2023年09月07日 [査読有り]
   

  The rapid melt of snow and sea ice during the Arctic summer provides a significant source of low-salinity meltwater to the surface ocean on the local scale. The accumulation of this meltwater on, under, and around sea ice floes can result in relatively thin meltwater layers in the upper ocean. Due to the small-scale nature of these upper-ocean features, typically on the order of 1 m thick or less, they are rarely detected by standard methods, but are nevertheless pervasive and critically important in Arctic summer. Observations during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition in summer 2020 focused on the evolution of such layers and made significant advancements in understanding their role in the coupled Arctic system. Here we provide a review of thin meltwater layers in the Arctic, with emphasis on the new findings from MOSAiC. Both prior and recent observational datasets indicate an intermittent yet long-lasting (weeks to months) meltwater layer in the upper ocean on the order of 0.1 m to 1.0 m in thickness, with a large spatial range. The presence of meltwater layers impacts the physical system by reducing bottom ice melt and allowing new ice formation via false bottom growth. Collectively, the meltwater layer and false bottoms reduce atmosphere-ocean exchanges of momentum, energy, and material. The impacts on the coupled Arctic system are far-reaching, including acting as a barrier for nutrient and gas exchange and impacting ecosystem diversity and productivity.
• Distribution of stable oxygen isotope in seawater and implication on freshwater cycle off the coast from Wilkes to George V Land, East Antarctica

  Shigeru Aoki, Kaihe Yamazaki, Daisuke Hirano, Daiki Nomura, Hiroto Murase

  Progress in Oceanography 217 103101 - 103101 2023年09月 [査読有り]
  
• Meltwater layer dynamics in a central Arctic lead: Effects of lead width, re-freezing, and mixing during late summer

  Nomura, D, Kawaguchi, Y, Webb, A, Li, Y, Dall’osto, M, Schmidt, K, Droste, E. S, Chamberlain, E. J, Kolabutin, N, Shimanchuk, E, Hoppmann, M, Gallagher, M. R, Meyer, H, Mellat, M, Bauch, D, Gabarró, C, Smith, M. M, Inoue, J, Damm, E, Delille, B

  Elementa, Science of the Anthropocene 11 1 2023年05月 [査読有り]
  
• Biogeochemical characteristics of brash sea ice and icebergs during summer and autumn in the Indian sector of the Southern Ocean

  Daiki Nomura, Reishi Sahashi, Keigo D. Takahashi, Ryosuke Makabe, Masato Ito, Manami Tozawa, Pat Wongpan, Ryo Matsuda, Masayoshi Sano, Michiyo Yamamoto-Kawai, Natsumi Nojiro, Aiko Tachibana, Norio Kurosawa, Masato Moteki, Takeshi Tamura, Shigeru Aoki, Hiroto Murase

  Progress in Oceanography 214 103023 - 103023 2023年04月 [査読有り]
  
• Light Under Arctic Sea Ice in Observations and Earth System Models

  Marion Lebrun, Martin Vancoppenolle, Gurvan Madec, Marcel Babin, Guislain Becu, Antonio Lourenço, Daiki Nomura, Frederic Vivier, Bruno Delille

  Journal of Geophysical Research: Oceans 128 3 2023年03月02日 [査読有り]
  
• Significant nutrient consumption in the dark subsurface layer during a diatom bloom: a case study on Funka Bay, Hokkaido, Japan

  Sachi Umezawa, Manami Tozawa, Yuichi Nosaka, Daiki Nomura, Hiroji Onishi, Hiroto Abe, Tetsuya Takatsu, Atsushi Ooki

  Biogeosciences 20 2 421 - 438 2023年01月27日 [査読有り]
   

  Abstract. We conducted repetitive observations in Funka Bay,Hokkaido, Japan, on 15 February, 4 and 15 March, and 14 April 2019. Thediatom spring bloom peaked on 4 March and started declining on 15 March.Funka Bay winter water remained below 30 m depth, which was below thesurface mixed-layer and dark-layer depth (0.1 % of the surface photosynthetically active radiation, PAR, depth) on 4and 15 March. In the subsurface layer at depths of 30–50 m, concentrationsof NO3-, PO43-, and Si(OH)4 decreased by halfbetween these dates, even in the dark. Incubation experiments using thediatom Thalassiosira nordenskioeldii showed that this diatom could consume added nutrients in the dark atsubstantial rates after pre-culturing to deplete nutrients. Incubationexperiments using natural seawater collected in the growing phase of the bloom on 8 March 2022 also showed that nutrient-depleted phytoplankton could consumeadded nutrients in the dark. We excluded three physicalprocess – water mixing, diffusive transport, and subduction – as possible mainreasons for the decrease in nutrients in the subsurface layer. We concludethat the nutrient reduction in the subsurface layer (30–50 m) between 4 and15 March 2019 could be explained by nutrient consumption by diatoms in the dark in thatlayer.
• The Interannual Variability of Sea Ice Area, Thickness, and Volume in the Southern Sea of Okhotsk and Its Likely Factors

  Takenobu Toyota, Noriaki Kimura, Jun Nishioka, Masato Ito, Daiki Nomura, Humio Mitsudera

  Journal of Geophysical Research: Oceans 127 12 2022年12月 [査読有り][通常論文]
  
• Factors controlling the precipitation of ikaite crystals within sea ice in a laboratory experiment

  Haruka NAKAJIMA, Daiki NOMURA

  Journal of the Japanese Society of Snow and Ice 84 6 503 - 514 2022年11月15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.
• First results of the ARIEL L-band radiometer on the MOSAiC Arctic Expedition during the late summer and autumn period

  Carolina Gabarró, Pau Fabregat, Ferran Hernández-Macià, Roger Jove, Joaquin Salvador, Gunnar Spreen, Linda Thielke, Ruzica Dadic, Marcus Huntemann, Nikolai Kolabutin, Daiki Nomura, Henna-Reetta Hannula, Martin Schneebeli

  Elementa: Science of the Anthropocene 10 1 2022年09月23日 [査読有り]
   

  Arctic sea ice is changing rapidly. Its retreat significantly impacts Arctic heat fluxes, ocean currents, and ecology, warranting the continuous monitoring and tracking of changes to sea ice extent and thickness. L-band (1.4 GHz) microwave radiometry can measure sea ice thickness for thin ice ≤1 m, depending on salinity and temperature. The sensitivity to thin ice makes L-band measurements complementary to radar altimetry which can measure the thickness of thick ice with reasonable accuracy. During the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, we deployed the mobile ARIEL L-band radiometer on the sea ice floe next to research vessel Polarstern to study the sensitivity of the L-band to different sea ice parameters (e.g., snow and ice thickness, ice salinity, ice and snow temperature), with the aim to help improve/validate current microwave emission models. Our results show that ARIEL is sensitive to different types of surfaces (ice, leads, and melt ponds) and to ice thickness up to 70 cm when the salinity of the sea ice is low. The measurements can be reproduced with the Burke emission model when in situ snow and ice measurements for the autumn transects were used as model input. The correlation coefficient for modeled Burke brightness temperature (BT) versus ARIEL measurements was approximately 0.8. The discrepancy between the measurements and the model is about 5%, depending on the transects analyzed. No explicit dependence on snow depth was detected. We present a qualitative analysis for thin ice observations on leads. We have demonstrated that the ARIEL radiometer is an excellent field instrument for quantifying the sensitivity of L-band radiometry to ice and snow parameters, leading to insights that can enhance sea ice thickness retrievals from L-band radiometer satellites (such as Soil Moisture Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP)) and improve estimates of Arctic sea-ice thickness changes on a larger scale.
• Impacts of basal melting of the Totten Ice Shelf and biological productivity on marine biogeochemical components in Sabrina Coast, East Antarctica

  Tetsuya P. Tamura, Daiki Nomura, Daisuke Hirano, Takeshi Tamura, Masaaki Kiuchi, Gen Hashida, Ryosuke Makabe, Kazuya Ono, Shuki Ushio, Kaihe Yamazaki, Yoshihiro Nakayama, Keigo D. Takahashi, Hiroko Sasaki, Hiroto Murase, Shigeru Aoki

  Global Biogeochemical Cycles 2022年09月13日 [査読有り]
   

  Abstract To clarify the impacts of basal melting of the Antarctic ice sheet and biological productivity on biogeochemical processes in Antarctic coastal waters, concentrations of dissolved inorganic carbon (DIC), total alkalinity (TA), inorganic nutrients, chlorophyll a, and stable oxygen isotopic ratios (δ¹⁸O) were measured from the offshore slope to the ice front of the Totten Ice Shelf (TIS) during the spring/summer of 2018, 2019, and 2020. Modified Circumpolar Deep Water (mCDW) intruded onto the continental shelf off the TIS and flowed along bathymetric troughs into the TIS cavity, where it formed a buoyant mixture with glacial meltwater from the ice shelf base. Physical oceanographic processes mostly determined the distributions of DIC, TA, and nutrient concentrations. However, photosynthesis and dilution by meltwater from sea ice and the ice shelf base decreased DIC, TA, and nutrient concentrations in surface water near the ice front. These causes also reduced the CO₂ partial pressure in surface water by more than 100 μatm with respect to mCDW in austral summer of 2018 and 2020, and the surface water became a strong CO₂ sink for the atmosphere. Phytoplankton photosynthesis changed DIC and TA in a molar ratio of 106:16. Thus, CO₂ partial pressure decreased mostly as a result of photosynthesis while dilution by glacial and sea ice meltwater had a small effect. The nutrient consumption ratio suggested that photosynthesis was stimulated by iron in the water column, supplied to the surface layer via buoyancy‐driven upwelling and basal ice shelf meltwater in addition to sea ice meltwater.
• Methane release from open leads and new ice following an Arctic winter storm event

  Anna Silyakova, Daiki Nomura, Marie Kotovitch, Agneta Fransson, Bruno Delille, Melissa Chierici, Mats A. Granskog

  Polar Science 33 100874 - 100874 2022年09月 [査読有り]
  
• Turbulent Mixing During Late Summer in the Ice–Ocean Boundary Layer in the Central Arctic Ocean: Results From the MOSAiC Expedition

  Yusuke Kawaguchi, Zoé Koenig, Daiki Nomura, Mario Hoppmann, Jun Inoue, Ying‐Chih Fang, Kirstin Schulz, Michael Gallagher, Christian Katlein, Marcel Nicolaus, Benjamin Rabe

  Journal of Geophysical Research: Oceans 127 8 2022年08月 [査読有り]
  
• 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 [査読有り]
   

  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.
• Effects of Snow and Remineralization Processes on Nutrient Distributions in Multi‐Year Antarctic Landfast Sea Ice

  Reishi Sahashi, Daiki Nomura, Takenobu Toyota, Manami Tozawa, Masato Ito, Pat Wongpan, Kazuya Ono, Daisuke Simizu, Kazuhiro Naoki, Yuichi Nosaka, Takeshi Tamura, Shigeru Aoki, Shuki Ushio

  Journal of Geophysical Research: Oceans 127 7 2022年07月 [査読有り]
  
• Primary productivity and phytoplankton community structure in surface waters of the western subarctic Pacific and the Bering Sea during summer with reference to bloom stages

  Hisatomo Waga, Amane Fujiwara, Toru Hirawake, Koji Suzuki, Kazuhiro Yoshida, Hiroto Abe, Daiki Nomura

  Progress in Oceanography 201 102738 - 102738 2022年02月 [査読有り]
   

  The western subarctic Pacific and adjacent Bering Sea are recognized as one of the most productive regions supported by spring diatom bloom among the world's oceans. Yet, phytoplankton growth and photosynthesis are often suppressed during summer. Little is known about factors controlling the summer primary productivity and phytoplankton community structure in the western subarctic Pacific and the Bering Sea, especially along the Russian coast extending from the Kuril Islands to the Gulf of Anadyr. A total of 24 stations belonging to two cruises conducted in June 2014 and August 2018 was categorized into three groups using hierarchical cluster analysis for physical properties such as seawater temperature, salinity, and mixed layer depth. Based on the biogeochemical characteristics of each cluster, we defined clusters 1, 2, and 3 as bloom, post-bloom, and pre-bloom conditions, respectively. Cluster 1, observed near the Kuril Islands and the Kamchatka Peninsula, was characterized by nutrient-rich cold water that supported the predominance of diatoms. Nutrient-depleted warm waters associated with shallow mixed-layer and small diatom populations were grouped into cluster 2, distributed in the Gulf of Anadyr and near the Kamchatka Peninsula. The deepest mixed layer depth was found in cluster 3, accompanied by the low proportions of diatoms. The spatial distribution of cluster 3 showed broad geographical coverages extending from the Kuril Islands to the Aleutian Basin. Thus, this study identified the relationships between summer primary productivity, phytoplankton community composition, and environmental variables in surface waters of the subarctic Pacific along the Russian coast. Overall, the present study addressed the shortcoming of in situ data in phytoplankton communities and environmental variables in the western subarctic Pacific and the Bering Sea.
• Nutrient consumption by diatoms in the dark subsurface layer of Funka Bay, Hokkaido, Japan

  Sachi Umezawa, Manami Tozawa, Yuichi Nosaka, Daiki Nomura, Hiroji Onishi, Hiroto Abe, Tetsuya Takatsu, Atsushi Ooki

  2022年01月06日 [査読有り]
   

  Abstract. We conducted time-series observations in Funka Bay, Hokkaido, Japan, from 15 February to 14 April 2019. The diatom spring bloom peaked on 4 March and started declining on 15 March. Funka Bay winter water remained below 30-m depth, which was below the surface mixed-layer and dark-zone depths on both dates. At depths of 30–50 m, concentrations of NO3–, PO43–, and Si(OH)4 decreased by half between these dates even in darkness. Incubation experiments using the diatom Thalassiosira nordenskioeldii showed that this diatom could consume nutrients in darkness at substantial rates. We conclude that the nutrient reduction in the subsurface layer (30–50 m) could be explained by dark consumption by diatoms that had been growing in the surface waters and then sank to the subsurface layer. We believe that this is the first study to present observational evidence for the consumption of the main nutrients by diatoms in the dark subsurface layer during the spring bloom. Nutrient consumption in this layer might have a substantial influence on the primary production during and after the spring bloom.
• Isoprene production in the water column and sediment in Funka Bay, Hokkaido, Japan

  Atsushi Ooki, Naoya Miyashita, Sachi Umezawa, Manami Tozawa, Yuichi Nosaka, Daiki Nomura, Hiroji Onishi, Hiroto Abe, Tetsuya Takatsu

  GEOCHEMICAL JOURNAL 56 5 142 - 150 2022年 [査読有り]
  
• Atmosphere-sea ice-ocean interaction study in Saroma-ko Lagoon, Hokkaido, Japan 2021

  Daiki NOMURA, Hiroki IKAWA, Yusuke KAWAGUCHI, Naoya KANNA, Tatsuya KAWAKAMI, Yuichi NOSAKA, Sachi UMEZAWA, Manami TOZAWA, Takahito HORIKAWA, Reishi SAHASHI, Taichi NOSHIRO, Ibuki KABA, Makoto OZAKI, Fumiyoshi KONDO, Keisuke ONO, Itsuka S. YABE, Eun Yae SON, Takahiro TOYODA, Sohiko KAMEYAMA, Changqing WANG, Hajime OBATA, Atsushi OOKI, Hiromichi UENO, Akihide KASAI

  Bulletin of Glaciological Research 40 1 - 17 公益社団法人 日本雪氷学会 2022年 [査読有り]
  
• Seasonal Variations and Drivers of Surface Ocean pCO2 in the Seasonal Ice Zone of the Eastern Indian Sector, Southern Ocean

  Manami Tozawa, Daiki Nomura, Shin‐ichiro Nakaoka, Masaaki Kiuchi, Kaihe Yamazaki, Daisuke Hirano, Shigeru Aoki, Hiroko Sasaki, Hiroto Murase

  Journal of Geophysical Research: Oceans 127 1 2022年01月 [査読有り]
   

  To quantitatively assess the inorganic carbon cycle in the eastern Indian sector of the Southern Ocean (80–150°E, south of 60°S), we measured ocean surface temperature, salinity, total alkalinity (TA), the partial pressure of carbon dioxide (pCO2), and concentrations of chlorophyll-a (chl a), dissolved inorganic carbon (DIC), and nutrients during the KY18 survey (December 2018–January 2019). The sea–air CO2 flux in this region was −8.3 ± 12.7 mmol m−2 day−1 (−92.1 to +10.6 mmol m−2 day−1). The ocean was therefore a weak CO2 sink. Based on the DIC and TA in the temperature minimum layer, we estimated the change of pCO2 from winter to summer (δpCO2) due to changes in water temperature, salinity, and biological activity (photosynthesis). The spatial distribution of pCO2 in the western part (80–110°E) of the study area was mainly driven by biological activity, which decreased pCO2 from December to early January, and in the eastern part (110–150°E) by temperature, which increased pCO2 from January to February. We also examined the changes in the CO2 concentrations (xCO2) over time by comparing data from 1996 with our data (2018–2019). The oceanic and atmospheric xCO2 increased by 23 and 45 ppm in 23 years, respectively. These changes of ocean xCO2 were mainly driven by an increase in CO2 uptake from the atmosphere as a result of the rise in atmospheric xCO2 and increase in biological activity associated with the change in the water-mass distribution.
• Decadal vision in oceanography 2021: Polar oceans

  Michiyo Yamamoto-Kawai, Takeshi Tamura, Eiji Watanabe, Jun Nishioka, Daiki Nomura, Ryusuke Makabe, Kohei Mizobata, Yasunaka Sayaka

  Oceanography in Japan 30 5 159 - 178 2021年11月15日 [査読有り]
  
• Salinity regime of the northwestern Bering Sea shelf

  Hiroto Abe, Daiki Nomura, Toru Hirawake

  Progress in Oceanography 198 102675 - 102675 2021年11月 [査読有り]
   

  The present study has examined the long-term variability of water mass properties and its relation to sea ice production (SIP) in the northwestern Bering Sea shelf using hydrographic and satellite data, and output from atmospheric reanalysis. As per our analysis of hydrographic data in the summer seasons, significant variability in bottom water temperature and salinity was noted. The temperature in 2018 showed particularly remarkable warming of the whole water column throughout the Gulf of Anadyr (GOA) and cold pool (CP) region. These oceanic parameters exhibited correlations with SIP in the Anadyr polynya, which is identified as one of the most active polynyas in the Northern Hemisphere. Specifically, there were more saline and colder water during high-SIP years, suggesting the influence of dense shelf water (DSW) that is formed during freezing processes; however, in low SIP years, bottom salinity has been observed to behave inversely, resulting in more saline water with lower SIP. We suggest that the influence of warm and saline water, originating from the Pacific, transported by ocean currents intensified by wintertime southerly winds in low-SIP years. The properties of bottom water in the semi-closed GOA are influenced by intrusion of the Pacific-originated water and DSW.
• Iron and nutrient dynamics along the East Kamchatka Current, western Bering Sea Basin and Gulf of Anadyr

  Jun Nishioka, Toru Hirawake, Daiki Nomura, Youhei Yamashita, Kazuya Ono, Aiko Murayama, Alexey Shcherbinin, Yuri N. Volkov, Humio Mitsudera, Naoto Ebuchi, Masaaki Wakatsuchi, Ichiro Yasuda

  Progress in Oceanography 198 102662 - 102662 2021年11月 [査読有り]
  
• Climate change impacts on sea-ice ecosystems and associated ecosystem services

  Nadja S. Steiner, Jeff Bowman, Karley Campbell, Melissa Chierici, Eeva Eronen-Rasimus, Marianne Falardeau, Hauke Flores, Agneta Fransson, Helena Herr, Stephen J Insley, Hanna M. Kauko, Delphine Lannuzel, Lisa Loseto, Amanda Lynnes, Andy Majewski, Klaus M. Meiners, Lisa A. Miller, Loïc N. Michel, Sebastien Moreau, Melissa Nacke, Daiki Nomura, Letizia Tedesco, Jan Andries van Franeker, Maria A van Leeuwe, Pat Wongpan

  Elementa: Science of the Anthropocene 9 1 2021年10月13日 [査読有り]
   

  A rigorous synthesis of the sea-ice ecosystem and linked ecosystem services highlights that the sea-ice ecosystem supports all 4 ecosystem service categories, that sea-ice ecosystems meet the criteria for ecologically or biologically significant marine areas, that global emissions driving climate change are directly linked to the demise of sea-ice ecosystems and its ecosystem services, and that the sea-ice ecosystem deserves specific attention in the evaluation of marine protected area planning. The synthesis outlines (1) supporting services, provided in form of habitat, including feeding grounds and nurseries for microbes, meiofauna, fish, birds and mammals (particularly the key species Arctic cod, Boreogadus saida, and Antarctic krill, Euphausia superba, which are tightly linked to the sea-ice ecosystem and transfer carbon from sea-ice primary producers to higher trophic level fish, mammal species and humans); (2) provisioning services through harvesting and medicinal and genetic resources; (3) cultural services through Indigenous and local knowledge systems, cultural identity and spirituality, and via cultural activities, tourism and research; (4) (climate) regulating services through light regulation, the production of biogenic aerosols, halogen oxidation and the release or uptake of greenhouse gases, for example, carbon dioxide. The ongoing changes in the polar regions have strong impacts on sea-ice ecosystems and associated ecosystem services. While the response of sea-ice–associated primary production to environmental change is regionally variable, the effect on ice-associated mammals and birds is predominantly negative, subsequently impacting human harvesting and cultural services in both polar regions. Conservation can help protect some species and functions. However, the key mitigation measure that can slow the transition to a strictly seasonal ice cover in the Arctic Ocean, reduce the overall loss of sea-ice habitats from the ocean, and thus preserve the unique ecosystem services provided by sea ice and their contributions to human well-being is a reduction in carbon emissions.
• Water mass distribution in the northern Bering and southern Chukchi seas using light absorption of chromophoric dissolved organic matter

  Toru Hirawake, Joji Oida, Youhei Yamashita, Hisatomo Waga, Hiroto Abe, Jun Nishioka, Daiki Nomura, Hiromichi Ueno, Atsushi Ooki

  Progress in Oceanography 197 102641 - 102641 2021年09月 [査読有り]
   

  The northern Bering Sea (NBS) and southern Chukchi Sea (SCS) contain several water masses with different characteristics that have been conventionally classified using temperature and salinity data. However, recent warming and sea ice decline can change these water properties, which suggests that classifying water masses using temperature–salinity diagrams could be problematic for this region. We used the light absorption coefficient of chromophoric dissolved organic matter (CDOM), aCDOM, as an alternative way to classify water masses. The aCDOM spectra of several water depths were measured in the NBS, the Gulf of Anadyr included, and SCS in July 2017 and 2018, and August 2018. Optical parameters that indicate CDOM quantity and quality, aCDOM(350) and spectral slopes (S275–295 and S350–400), were calculated for each sample; water masses were classified using cluster analysis. When surface waters in the NBS and SCS are classified on the basis of the conventional method using a temperature–salinity diagram, they are mistakenly identified as Alaskan Coastal Water because of warmer temperatures. However, our cluster analysis using CDOM parameters evenly classified seven water masses with reasonable distributions. A water mass with the highest aCDOM(350) and lowest S275–295 was found along the coast of the Gulf of Anadyr and Alaska mainland, which suggests that freshwater originates from the Anadyr and Yukon rivers and is transported by the Anadyr Current and Alaskan Coastal Current, respectively. A CDOM-based water mass with high S275–295, indicating CDOM degradation by ultraviolet radiation, was present at the sea surface. A water mass with low S275–295 was found at deeper water depths and river mouths. These results suggest that classification with CDOM parameters is consistent with geographical features. In addition, we recognized a water mass with high nitrate concentrations, which is likely Anadyr Water that originates in the region from the Bering Slope to the Gulf of Anadyr. Overall, this study reveals that water mass classification using CDOM parameters is useful in coastal sea areas in which water mass mixing is complex.
• Formation of dense shelf water associated with sea ice freezing in the Gulf of Anadyr estimated with oxygen isotopic ratios

  Daiki Nomura, Hiroto Abe, Toru Hirawake, Atsushi Ooki, Youhei Yamashita, Aiko Murayama, Kazuya Ono, Jun Nishioka

  Progress in Oceanography 196 102595 - 102595 2021年08月 [査読有り]
   

  We analyzed temperature and salinity data and oxygen isotope ratios (δ18O) in summer 2018 in order to quantify the formation of dense shelf water (DSW) associated with sea ice freezing in the Gulf of Anadyr in the northwestern Bering Sea. Salinity and δ18O displayed a strong linear relationship in samples upstream (southwest) of the Gulf of Anadyr. However, in bottom water (>26.5 σθ) in the northern Gulf of Anadyr, where a large polynya is the site of high sea ice production in winter, salinity was clearly higher than in the upstream water, whereas δ18O was in the same range. This deviation is consistent with the formation of sea ice through brine rejection and subsequent DSW formation, causing an increase of salinity without changing δ18O. A mass balance calculation based on these results yielded an estimated production of sea ice equivalent to a thickness 0.7 m, a result that matched an independent estimate of 2018 annual ice production based on satellite data. Even though the winter of 2018 had a historically low sea ice extent in the Bering Sea, including the Gulf of Anadyr, our results indicate continued DSW formation in the Gulf of Anadyr.
• The Effect of Basal Melting of the Shirase Glacier Tongue on the CO 2 System in Lützow‐Holm Bay, East Antarctica

  Masaaki Kiuchi, Daiki Nomura, Daisuke Hirano, Takeshi Tamura, Gen Hashida, Shuki Ushio, Daisuke Simizu, Kazuya Ono, Shigeru Aoki

  Journal of Geophysical Research: Biogeosciences 126 5 2021年05月 [査読有り]
   

  To clarify the effect of basal melting of ice tongues/ice shelf on the CO2 system in the Antarctic continental margin, seawater samples were collected for analysis of dissolved inorganic carbon (DIC), total alkalinity (TA), nutrients, chlorophyll a (chl.a), and oxygen isotopic ratios at the ice front of the Shirase Glacier Tongue (SGT) in Lützow-Holm Bay (LHB), East Antarctica during the summers of 2017 and 2018. At depths greater than ∼20 dbar in LHB, CO2 system parameters were strongly influenced by the dilution effect of SGT basal melting and the inflow of modified Circumpolar Deep Water (mCDW). The distributions of DIC and TA agreed well with an offshore origin of mCDW that flowed beneath the SGT and mixing of basal meltwater and mCDW beneath the SGT. The fraction of SGT meltwater was highest at the station near the ice front. Dilution by SGT basal meltwater reduced the partial pressure of CO2 in the mCDW from 431 to 387 μatm. The water then became a sink rather than source of atmospheric CO2. In the sea surface, DIC and TA were strongly influenced by biological processes. Salinity-normalized DIC decreased with the increase of salinity-normalized TA in accord with 106:16 C:N molar stoichiometry; the chl.a concentration at the sea surface was as high as 31 μg L−1.
• 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 Bjørk, Toku Oshima

  Polar Science 27 100632 - 100632 2021年03月 [査読有り]
   

  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.
• The future of Arctic sea-ice biogeochemistry and ice-associated ecosystems

  Delphine Lannuzel, Letizia Tedesco, Maria van Leeuwe, Karley Campbell, Hauke Flores, Bruno Delille, Lisa Miller, Jacqueline Stefels, Philipp Assmy, Jeff Bowman, Kristina Brown, Giulia Castellani, Melissa Chierici, Odile Crabeck, Ellen Damm, Brent Else, Agneta Fransson, François Fripiat, Nicolas-Xavier Geilfus, Caroline Jacques, Elizabeth Jones, Hermanni Kaartokallio, Marie Kotovitch, Klaus Meiners, Sébastien Moreau, Daiki Nomura, Ilka Peeken, Janne-Markus Rintala, Nadja Steiner, Jean-Louis Tison, Martin Vancoppenolle, Fanny Van der Linden, Marcello Vichi, Pat Wongpan

  Nature Climate Change 10 11 983 - 992 2020年11月 [査読有り]
  
• 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 [査読有り][通常論文]
  
• Implications of Sea Ice Management for Arctic Biogeochemistry

  Lisa Miller, Francois Fripiat, Sebastien Moreau, Daiki Nomura, Jacqueline Stefels, Nadja Steiner, Letizia Tedesco, Martin Vancoppenolle

  Eos 101 2020年09月30日 [査読有り]
   

  Geoengineering strategies to slow sea ice melting would affect not only Earth's climate but also the biology and chemistry of the oceans, atmosphere, and ice.
• Using under-ice hyperspectral transmittance to determine land-fast sea-ice algal biomass in Saroma-ko Lagoon, Hokkaido, Japan

  Pat Wongpan, Daiki Nomura, Takenobu Toyota, Tomonori Tanikawa, Klaus M. Meiners, Tomomi Ishino, Tetsuya P. Tamura, Manami Tozawa, Yuichi Nosaka, Toru Hirawake, Atsushi Ooki, Shigeru Aoki

  Annals of Glaciology 61 83 1 - 10 2020年09月24日 [査読有り][通常論文]
   

  Sea ice, which forms in polar and nonpolar areas, transmits light to ice-associated (sympagic) algal communities. To noninvasively study the distribution of sea-ice algae, empirical relations to estimate its biomass from under-ice hyperspectral irradiance have been developed in the Arctic and Antarctica but lack for nonpolar regions. This study examines relationships between normalised difference indices (NDI) calculated from hyperspectral transmittance and sympagic algal biomass in the nonpolar Saroma-ko Lagoon. We analysed physico-biogeochemical properties of snow and land-fast sea ice supporting 27 paired bio-optical measurements along three transects covering an area of over 250 m × 250 m in February 2019. Snow depth (0.08 ± 0.01 m) and ice-bottom brine volume fraction (0.21 ± 0.02) showed low (0.06) and high (0.58) correlations with sea-ice core bottom section chlorophyll a (Chl. a), respectively. Spatial analyses unveiled the patch size of sea-ice Chl. a to be ~65 m, which is in the same range reported from previous studies. A selected NDI (669, 596 nm) explained 63% of algal biomass variability. This reflects the bio-optical properties and environmental conditions of the lagoon that favour the wavelength pair in the orange/red part of the spectrum and suggests the necessity of a specific bio-optical relationship for Saroma-ko Lagoon.
• Strong biological carbon uptake and carbonate chemistry associated with dense shelf water outflows in the Cape Darnley polynya, East Antarctica

  Kan Murakami, Daiki Nomura, Gen Hashida, Shin ichiro Nakaoka, Yujiro Kitade, Daisuke Hirano, Toru Hirawake, Kay I. Ohshima

  Marine Chemistry 225 103842 - 103842 2020年09月10日 [査読有り][通常論文]
   

  © 2020 Elsevier B.V. Formation of dense shelf water (DSW) in coastal polynyas (open water or thin sea-ice cover) in the sea-ice zone around Antarctica supplies Antarctic Bottom Water (AABW) through overflow down the continental slope. In coastal polynyas, atmospheric carbon dioxide (CO2) is absorbed by the ocean in the early spring because of active primary production, and DSW formation is an important process for transporting this carbon from the sea surface to the deep ocean. However, there have been few quantitative evaluations of carbon consumption by active primary production and transport in coastal polynyas. Here, we examined the carbon dynamics in the Cape Darnley polynya (CDP), East Antarctica during austral summer 2009, by using carbonate system parameters combined with oceanographic mooring data. The partial pressure of CO2 in the CDP surface water was lower than that of the atmosphere and the mean and standard deviation of sea−air CO2 flux was estimated as −6.5 ± 6.9 mmol C m−2 d−1 (a negative value indicates absorption of atmospheric CO2 by the ocean). Vertical profiles of dissolved inorganic carbon (DIC) concentration showed that concentrations in the bottom layer near the ocean floor were lower (by about 20 μmol kg−1) than those in the ambient water (e.g., modified Circumpolar Deep Water, mCDW). The low-DIC in the shelf water was maintained by the strong biological uptake of carbon imported from high-DIC mCDW within the water column. Therefore, low-DIC DSW overflowed down the continental slope, and low-DIC concentrations were maintained through an export pathway to the continental shelf. The annual production of dissolved organic carbon and particulate organic carbon on the shelf was estimated as 0.7 × 1011–1.5 × 1011 mol C using the data for the DIC of DSW and current velocity data from a mooring in the CDP. Our results provide quantitative estimates for the potential role of carbon consumption by the active primary production and carbon transport by dense water formation in Antarctic coastal polynyas.
• Influence of glacial water and carbonate minerals on wintertime sea-ice biogeochemistry and the CO2 system in an Arctic fjord in Svalbard

  Agneta Fransson, Melissa Chierici, Daiki Nomura, Mats A. Granskog, Svein Kristiansen, Tõnu Martma, Gernot Nehrke

  Annals of Glaciology 1 - 21 2020年08月13日 [査読有り][通常論文]
   

  The effect of freshwater sources on wintertime sea-ice CO₂ processes was studied from the glacier front to the outer Tempelfjorden, Svalbard, in sea ice, glacier ice, brine and snow. March–April 2012 was mild, and the fjord was mainly covered with drift ice, in contrast to the observed thicker fast ice in the colder April 2013. This resulted in different physical and chemical properties of the sea ice and under-ice water. Data from stable oxygen isotopic ratios and salinity showed that the sea ice at the glacier front in April 2012 contained on average 54% of frozen-in glacial meltwater. This was five times higher than in April 2013, where the ice was frozen seawater. In April 2012, the largest excess of sea-ice total alkalinity (A_T), carbonate ion ([CO₃²⁻]) and bicarbonate ion concentrations ([HCO₃⁻]) relative to salinity was mainly related to dissolved dolomite and calcite incorporated during freezing of mineral-enriched glacial water. In April 2013, the excess of these variables was mainly due to ikaite dissolution as a result of sea-ice processes. Dolomite dissolution increased sea-ice A_T twice as much as ikaite and calcite dissolution, implying different buffering capacity and potential for ocean CO₂ uptake in a changing climate.
• Solidification effects of snowfall on sea-ice freeze-up: results from an onsite experimental study

  Takenobu Toyota, Takashi Ono, Tomonori Tanikawa, Pat Wongpan, Daiki Nomura

  Annals of Glaciology 61 83 1 - 10 2020年07月14日 [査読有り][通常論文]
   

  Although the effects of snow during sea-ice growth have been investigated for sea ice which is thick enough to accommodate dry snow, those for thin sea ice have not been paid much attention due to the difficulty in observing them. Observations are complicated by the presence of slush and its subsequent freeze-up, and the surface heat budget might be sensitive to the additional ice thickness. An onsite short-term land fast sea-ice freeze-up experiment in the Saroma-ko Lagoon, Hokkaido, Japan was carried out to examine the effects of snowfall on the structure and surface heat budget of thin sea ice, based on observational results and a 1-D thermodynamic model. We found that snowfall contributes to the solidification of the surface slush layer, contributing ice thickness that is comparable to the snowfall amount and affecting the crystal texture significantly. On the other hand, the basal ice growth rate and turbulent heat flux were not significantly affected, being <3.1 × 10⁻⁸ m s⁻¹ and 3 W m⁻², respectively. This finding may validate the omission in past studies of snow effect in estimating ice production rates in polynyas and has implications about the reconstruction of growth history from sample analysis.
• Physical and biological properties of early winter Antarctic sea ice in the Ross Sea

  Jean-Louis Tison, Ted Maksym, Alexander D. Fraser, Matthew Corkill, Noriaki Kimura, Yuichi Nosaka, Daiki Nomura, Martin Vancoppenolle, Steve Ackley, Sharon Stammerjohn, Sarah Wauthy, Fanny Van der Linden, Gauthier Carnat, Célia Sapart, Jeroen de Jong, François Fripiat, Bruno Delille

  Annals of Glaciology 1 - 19 2020年06月24日 [査読有り][通常論文]
   

  This work presents the results of physical and biological investigations at 27 biogeochemical stations of early winter sea ice in the Ross Sea during the 2017 PIPERS cruise. Only two similar cruises occurred in the past, in 1995 and 1998. The year 2017 was a specific year, in that ice growth in the Central Ross Sea was considerably delayed, compared to previous years. These conditions resulted in lower ice thicknesses and Chl-a burdens, as compared to those observed during the previous cruises. It also resulted in a different structure of the sympagic algal community, unusually dominated by Phaeocystis rather than diatoms. Compared to autumn-winter sea ice in the Weddell Sea (AWECS cruise), the 2017 Ross Sea pack ice displayed similar thickness distribution, but much lower snow cover and therefore nearly no flooding conditions. It is shown that contrasted dynamics of autumnal-winter sea-ice growth between the Weddell Sea and the Ross Sea impacted the development of the sympagic community. Mean/median ice Chl-a concentrations were 3–5 times lower at PIPERS, and the community status there appeared to be more mature (decaying?), based on Phaeopigments/Chl-a ratios. These contrasts are discussed in the light of temporal and spatial differences between the two cruises.
• Snow property controls on modelled Ku-band altimeter estimates of first-year sea ice thickness: Case studies from the Canadian and Norwegian Arctic

  Nandan V, Scharien R. K, Geldsetzer T, Kwok R, Yackel J. J, Mahmud M. S, Rösel A, Tonboe R, Granskog M, Willatt R, Stroeve J, Nomura D, Frey M.

  IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 13 1082 - 1096 2020年 [査読有り][通常論文]
  
• Saroma-ko Lagoon Observations for sea ice Physico-chemistry and Ecosystems 2019 (SLOPE2019)

  Daiki NOMURA, Pat WONGPAN, Takenobu TOYOTA, Tomonori TANIKAWA, Yusuke KAWAGUCHI, Takashi ONO, Tomomi ISHINO, Manami TOZAWA, Tetsuya P. TAMURA, Itsuka S. YABE, Eun Yae SON, Frederic VIVIER, Antonio LOURENCO, Marion LEBRUN, Yuichi NOSAKA, Toru HIRAWAKE, Atsushi OOKI, Shigeru AOKI, Brent ELSE, Francois FRIPIAT, Jun INOUE, Martin VANCOPPENOLLE

  Bulletin of Glaciological Research 38 0 1 - 12 2020年 [査読有り][通常論文]
  
• Fostering multidisciplinary research on interactions between chemistry, biology, and physics within the coupled cryosphere-atmosphere system

  Jennie L. Thomas, Jochen Stutz, Markus M. Frey, Thorsten Bartels-Rausch, Katye Altieri, Foteini Baladima, Jo Browse, Manuel Dall’Osto, Louis Marelle, Jeremie Mouginot, Jennifer G. Murphy, Daiki Nomura, Kerri A. Pratt, Megan D. Willis, Paul Zieger, Jon Abbatt, Thomas A. Douglas, Maria Cristina Facchini, James France, Anna E. Jones, Kitae Kim, Patricia A. Matrai, V. Faye McNeill, Alfonso Saiz-Lopez, Paul Shepson, Nadja Steiner, Kathy S. Law, Steve R. Arnold, Bruno Delille, Julia Schmale, Jeroen E. Sonke, Aurélien Dommergue, Didier Voisin, Megan L. Melamed, Jessica Gier

  Elem Sci Anth 7 1 58 - 58 2019年12月30日 [査読有り][通常論文]
  
• Isoprene production in seawater of Funka Bay, Hokkaido, Japan

  Atsushi Ooki, Ryuta Shida, Masashi Otsu, Hiroji Onishi, Naoto Kobayashi, Takahiro Iida, Daiki Nomura, Kota Suzuki, Hideyoshi Yamaoka, Tetsuya Takatsu

  Journal of Oceanography 75 6 485 - 501 2019年12月 [査読有り][通常論文]
  
• The effect of melting treatments on the assessment of biomass and nutrients in sea ice (Saroma-ko lagoon, Hokkaido, Japan)

  Roukaerts A, Nomura D, Deman F, Hattori H, Dehairs F, Fripiat F

  Polar Biology, 42, 347–356, 2019. 2019年 [査読有り][通常論文]
  
• Production of Dibromomethane and Changes in the Bacterial Community in Bromoform-Enriched Seawater

  Takafumi Kataoka, Atsushi Ooki, Daiki Nomura

  Microbes and Environments 34 2 215 - 218 2019年 [査読有り][通常論文]
  
• Effects of glacier and sea ice melting on the biogeochemical cycles in the surface water of the Arctic Ocean

  Nomura D, Kanna N, Ooki A

  Chikyu-Kagaku (Geochemistry), In Japanese with English abstract, figures, and table, 53, 149-158, doi:10.14934/chikyukagaku.53.149, 2019. 2019年 [査読有り][通常論文]
  
• Biogeochemistry of bromine and organic sulfur compounds in the Arctic region

  Kameyama S, Ooki A, Nomura D

  Chikyu-Kagaku (Geochemistry), In Japanese with English abstract, and figures. 53, 159-171, doi:10.14934/chikyukagaku.53.159, 2019. 2019年 [査読有り][通常論文]
  
• Chlorophyll-a in Antarctic Landfast Sea Ice: A First Synthesis of Historical Ice Core Data

  K. M. Meiners, M. Vancoppenolle, G. Carnat, G. Castellani, B. Delille, D. Delille, G. S. Dieckmann, H. Flores, F. Fripiat, M. Grotti, B. A. Lange, D. Lannuzel, A. Martin, A. McMinn, D. Nomura, I. Peeken, P. Rivaro, K. G. Ryan, J. Stefels, K. M. Swadling, D. N. Thomas, J.-L. Tison, P. van der Merwe, M. A. van Leeuwe, C. Weldrick, E. J. Yang

  Journal of Geophysical Research: Oceans 123 11 8444 - 8459 2018年11月 [査読有り][通常論文]
  
• CO2 flux over young and snow-covered Arctic pack ice in winter and spring

  Daiki Nomura, Mats A. Granskog, Agneta Fransson, Melissa Chierici, Anna Silyakova, Kay I. Ohshima, Lana Cohen, Bruno Delille, Stephen R. Hudson, Gerhard S. Dieckmann

  Biogeosciences 15 11 3331 - 3343 2018年06月05日 [査読有り][通常論文]
   

  Abstract. Rare CO2 flux measurements from Arctic pack ice show that two types of ice contribute to the release of CO2 from the ice to the atmosphere during winter and spring: young, thin ice with a thin layer of snow and older (several weeks), thicker ice with thick snow cover. Young, thin sea ice is characterized by high salinity and high porosity, and snow-covered thick ice remains relatively warm ( >  −7.5 °C) due to the insulating snow cover despite air temperatures as low as −40 °C. Therefore, brine volume fractions of these two ice types are high enough to provide favorable conditions for gas exchange between sea ice and the atmosphere even in mid-winter. Although the potential CO2 flux from sea ice decreased due to the presence of the snow, the snow surface is still a CO2 source to the atmosphere for low snow density and thin snow conditions. We found that young sea ice that is formed in leads without snow cover produces CO2 fluxes an order of magnitude higher than those in snow-covered older ice (+1.0 ± 0.6 mmol C m−2 day−1 for young ice and +0.2 ± 0.2 mmol C m−2 day−1 for older ice).
• 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]
  
• Influence of Sea Ice Crack Formation on the Spatial Distribution of Nutrients and Microalgae in Flooded Antarctic Multiyear Ice

  Daiki Nomura, Shigeru Aoki, Daisuke Simizu, Takahiro Iida

  Journal of Geophysical Research: Oceans 123 2 939 - 951 2018年02月 [査読有り][通常論文]
  
• Effects of sea ice freezing and melting on air-sea CO2 exchange

  Nomura D

  Archives of Atmospheric Chemistry Research, In Japanese, 38, 038A03, 2018. 2018年 [査読有り][通常論文]
  
• Biogeochemical Impact of Snow Cover and Cyclonic Intrusions on the Winter Weddell Sea Ice Pack

  J.‐L. Tison, S. Schwegmann, G. Dieckmann, J.‐M. Rintala, H. Meyer, S. Moreau, M. Vancoppenolle, D. Nomura, S. Engberg, L. J. Blomster, S. Hendricks, C. Uhlig, A.‐M. Luhtanen, J. de Jong, J. Janssens, G. Carnat, J. Zhou, B. Delille

  Journal of Geophysical Research: Oceans 122 12 9548 - 9571 2017年12月 [査読有り][通常論文]
  
• Macro-nutrient concentrations in Antarctic pack ice: Overall patterns and overlooked processes

  François Fripiat, Klaus M. Meiners, Martin Vancoppenolle, Stathys Papadimitriou, David N. Thomas, Stephen F. Ackley, Kevin R. Arrigo, Gauthier Carnat, Stefano Cozzi, Bruno Delille, Gerhard S. Dieckmann, Robert B. Dunbar, Agneta Fransson, Gerhard Kattner, Hilary Kennedy, Delphine Lannuzel, David R. Munro, Daiki Nomura, Janne-Markus Rintala, Véronique Schoemann, Jacqueline Stefels, Nadja Steiner, Jean-Louis Tison

  Elem Sci Anth 5 0 13 - 13 2017年03月29日 [査読有り][通常論文]
  
• Effect of elevated CO 2 concentration on microalgal communities in Antarctic pack ice

  Thomas Coad, Andrew McMinn, Daiki Nomura, Andrew Martin

  Deep Sea Research Part II: Topical Studies in Oceanography 131 160 - 169 2016年09月 [査読有り]
  
• DMSP and DMS cycling within Antarctic sea ice during the winter-spring transition

  E. Damm, D. Nomura, A. Martin, G. S. Dieckmann, K. M. Meiners

  DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 131 150 - 159 2016年09月 [査読有り][通常論文]
   

  This study describes within-ice concentrations of dimethylsulfoniopropionate (DMSP), its degradation product dimethylsulphide (DMS), as well as nutrients and chlorophyll a, that were sampled during the Sea Ice Physics and Ecosystems eXperiment-2 (SIPEX-2) in 2012. DMSP is a methylated substrate produced in large amounts annually by ice-associated microalgae, while DMS plays a significant role in carbon and sulphur cycling in the Southern Ocean. In the East Antarctic study area between 115-125 degrees E and 64-66 degrees S, ice and slush cores, brine, under-ice seawater and zooplankton (Antarctic krill) samples were collected at 6 ice stations. The pack-ice was characterised by high snow loading which initiated flooding events and triggered nutrient supply to the sea-ice surface, while variation in ice conditions influenced sea-ice permeability. This ranged from impermeable surface and middle sections of the sea ice, to completely permeable ice cores at some stations. Chlorophyll a maxima shifted from the sea-ice surface horizon at the first station to the sea ice bottom layer at the last station. Highest DMSP concentrations were detected in brine samples at the sea-ice surface, reflecting a mismatch with respect to the distribution of chlorophyll a. Our data suggest enhanced DMSP production by sea-ice surface algal communities and its release into brine during freezing and melting, which in turn is coupled to flooding events early in the season. A time-cycle of DMS production by DMSP degradation and DMS efflux is evident at the sea ice-snow interface when slush is formed during melt. Seawater under the ice contained only low concentrations of DMSP and DMS, even when brine drainage was evident and the sea ice became permeable. We postulate that in situ grazing by zooplankton may act as sink for the DMSP produced early in the season. (C) 2016 Elsevier Ltd. All rights reserved.
• On the extraordinary snow on the sea ice off East Antarctica in late winter, 2012

  Takenobu Toyota, Robert Massom, Olivier Lecomte, Daiki Nomura, Petra Heil, Takeshi Tamura, Alexander D. Fraser

  DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 131 53 - 67 2016年09月 [査読有り][通常論文]
   

  In late winter-early spring 2012, the second Sea Ice Physics and Ecosystems Experiment (SIPEX II) was conducted off Wilkes Land, East Antarctica, onboard R/V Aurora Australis. The sea-ice conditions were characterized by significantly thick first-year ice and snow, trapping the ship for about 10 days in the near coastal region. The deep snow cover was particularly remarkable, in that its average value of 0.45 m was almost three times that observed between 1992 and 2007 in the region. To reveal factors responsible, we used in situ observations and ERA-Interim reanalysis (1990-2012) to examine the relative contribution of the different components of the local-regional snow mass balance equation i.e., snow accumulation on sea ice, precipitation minus evaporation (P-E), and loss by (i) snow-ice formation and (ii) entering into leads due to drifting snow. Results show no evidence for significantly high P-E in the winter of 2012. Ice core analysis has shown that although the snow-ice layer was relatively thin, indicating less transformation from snow to snow-ice in 2012 as compared to measurements from 2007, the difference was not enough to explain the extraordinarily deep snow. Based on these results, we deduce that lower loss of snow into leads was probably responsible for the extraordinary snow in 2012. Statistical analysis and satellite images suggest that the reduction in loss of snow into leads is attributed to rough ice surface associated with active deformation processes and larger floe size due to sea-ice expansion. This highlights the importance of snow-sea ice interaction in determining the mean snow depth on Antarctic sea ice. (C) 2016 Elsevier Ltd. All rights reserved.
• Potential changes in feeding behavior of Antarctic fish, Pseudotrematomus bernacchii (Boulenger, 1902) on the East Ongul Island, Antarctica

  Suchana Chavanich, Voranop Viyakarn, Daiki Nomura, Kentaro Watanabe

  POLAR SCIENCE 9 4 389 - 392 2015年12月 [査読有り][通常論文]
   

  The feeding habits of the Antarctic fish Pseudotrematomus bernacchii (Previous name: Trematomus bernacchii) under the fast ice around Japanese Syowa Station were investigated in the summers of 2004/2005 and 2009/2010. The results showed that amphipods and krill were the major prey. However, there was a significant difference in the proportions of larger invertebrates such as squids, octopus and other crustaceans found in the fish stomachs between 2009/2010 and the previous years. Moreover, the percentage of amphipods and krill in fish stomachs declined over the 5-year period in all fish size classes. Several factors including sea ice melting, habitat and environmental changes might have influenced the pattern of feeding behavior. (C) 2015 Elsevier B.V. and NIPR. All rights reserved.
• A global-scale map of isoprene and volatile organic iodine in surface seawater of the Arctic, Northwest Pacific, Indian, and Southern Oceans

  Atsushi Ooki, Daiki Nomura, Shigeto Nishino, Takashi Kikuchi, Yoko Yokouchi

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 120 6 4108 - 4128 2015年06月 [査読有り][通常論文]
   

  Isoprene (C5H8) and three volatile organic iodine compounds (VOIs: CH3I, C2H5I, and CH2ClI) in surface seawater were measured in the western Arctic, Northwest Pacific, Indian, and Southern Oceans during the period 2008-2012. These compounds are believed to play an important role in the marine atmospheric chemistry after their emission. The measurements were performed with high time-resolution (1-6 h intervals) using an online equilibrator gas chromatography mass spectrometer. C5H8 was most abundant in high-productivity transitional waters and eutrophic tropical waters. The chlorophyll-a normalized production rates of C5H8 were high in the warm subtropical and tropical waters, suggesting the existence of a high emitter of C5H8 in the biological community of the warm waters. High concentrations of the three VOIs in highly productive transitional water were attributed to biological productions. For CH3I, the highest concentrations were widely distributed in the basin area of the oligotrophic subtropical NW Pacific, probably due to photochemical production and/or high emission rates from phytoplankton. In contrast, the lowest concentrations of C2H5I in subtropical waters were attributed to photochemical removal. Enhancement of CH2ClI concentrations in the shelf-slope areas of the Chukchi Sea and the transitional waters of the NW Pacific in winter suggested that vertical mixing with subsurface waters by regional upwelling or winter cooling acts to increase the CH2ClI concentrations in surface layer. Sea-air flux calculations revealed that the fluxes of CH2ClI were the highest among the three VOIs in shelf-slope areas; the CH3I flux was highest in basin areas.
• Effect of glacial drainage water on the CO2 system and ocean acidification state in an Arctic tidewater-glacier fjord during two contrasting years

  Agneta Fransson, Melissa Chierici, Daiki Nomura, Mats A. Granskog, Svein Kristiansen, Tonu Martma, Gernot Nehrke

  JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 120 4 2413 - 2429 2015年04月 [査読有り][通常論文]
   

  In order to investigate the effect of glacial water on the CO2 system in the fjord, we studied the variability of the total alkalinity (A(T)), total dissolved inorganic carbon (C-T), dissolved inorganic nutrients, oxygen isotopic ratio (O-18), and freshwater fractions from the glacier front to the outer Tempelfjorden on Spitsbergen in winter 2012 (January, March, and April) and 2013 (April) and summer/fall 2013 (September). The two contrasting years clearly showed that the influence of freshwater, mixing, and haline convection affected the chemical and physical characteristics of the fjord. The seasonal variability showed the lowest calcium carbonate saturation state () and pH values in March 2012 coinciding with the highest freshwater fractions. The highest and pH were found in September 2013, mostly due to CO2 uptake during primary production. Overall, we found that increased freshwater supply decreased , pH, and A(T). On the other hand, we observed higher A(T) relative to salinity in the freshwater end-member in the mild and rainy winter of 2012 (1142 mol kg(-1)) compared to A(T) in 2013 (526 mol kg(-1)). Observations of calcite and dolomite crystals in the glacial ice suggested supply of carbonate-rich glacial drainage water to the fjord. This implies that winters with a large amount of glacial drainage water partly provide a lessening of further ocean acidification, which will also affect the air-sea CO2 exchange.
• Methods for biogeochemical studies of sea ice: The state of the art, caveats, and recommendations

  Lisa A. Miller, Francois Fripiat, Brent G.T. Else, Jeff S. Bowman, Kristina A. Brown, R. Eric Collins, Marcela Ewert, Agneta Fransson, Michel Gosselin, Delphine Lannuzel, Klaus M. Meiners, Christine Michel, Jun Nishioka, Daiki Nomura, Stathys Papadimitriou, Lynn M. Russell, Lise Lotte Sørensen, David N. Thomas, Jean-Louis Tison, Maria A. van Leeuwe, Martin Vancoppenolle, Eric W. Wolff, Jiayun Zhou

  Elementa: Science of the Anthropocene 3 000038 - 000038 2015年01月23日 [査読有り][通常論文]
  
• 2012年東南極域海氷上で観測された異常積雪深に関する事例解析

  豊田 威信, R. Massom, O. Lecomte, 野村 大樹, P. Heil, 田村 岳史, A. Fraser

  雪氷研究大会講演要旨集 2015 32 - 32 公益社団法人 日本雪氷学会／日本雪工学会 2015年
• Evidence for significant protein-like dissolved organic matter accumulation in Sea of Okhotsk sea ice

  Mats A. Granskog, Daiki Nomura, Susann Muller, Andreas Krell, Takenobu Toyota, Hiroshi Hattori

  ANNALS OF GLACIOLOGY 56 69 1 - 8 2015年 [査読有り][通常論文]
   

  Absorption and fluorescence of chromophoric dissolved organic matter (CDOM) in sea ice and surface waters in the southern Sea of Okhotsk was examined. Sea-water CDOM had featureless absorption increasing exponentially with shorter wavelengths. Sea ice showed distinct absorption peaks in the ultraviolet, especially in younger ice. Older first-year sea ice had relatively flat absorption spectra in the ultraviolet range. Parallel factor analysis (PARAFAC) identified five fluorescent CDOM components, two humic-like and three protein-like. Sea water was largely governed by humic-like fluorescence. In sea ice, protein-like fluorescence was found in considerable excess relative to sea water. The accumulation of protein-like CDOM fluorescence in sea ice is likely a result of biological activity within the ice. Nevertheless, sea ice does not contribute excess CDOM during melt, but the material released will be of different composition than that present in the underlying waters. Thus, at least transiently, the CDOM introduced during sea-ice melt might provide a more labile source of fresher protein-like DOM to surface waters in the southern Sea of Okhotsk.
• Effects of sea-ice growth and decay processes on the biogeochemical cycles in the polar oceans

  Nomura D

  Umi no Kenkyu (Oceanography in Japan), In Japanese with English abstract and figures, 24, 2, 2015. 24 2 51 - 61 日本海洋学会 2015年 [査読有り][通常論文]
   

  海氷の生成と融解に伴う物理場の変化が極域海洋の物質循環過程に与える影響を把握するため,室内実験,フィールド観測を実施した。従来,海氷は,海洋表面を覆い,大気-海洋間の物質循環を妨げる"障壁"として認識されてきた。しかし,海氷は,気候変動に関わる温室効果ガスや揮発性有機化合物等の大気-海洋間の交換に重要な役割を果たしていることが分かってきた。本稿では,著者の研究グループが,これまで実施してきた海氷の生成と融解が極域海洋の物質循環に与える影響に関する研究を紹介する。In order to understand effects of sea-ice growth and decay processes on the biogeochemical cycles in the polar oceans, field observations in the Arctic, Antarctic, and Sea of Okhotsk as well as laboratory experiments were carried out. Sea-ice has not been considered in estimations of biogeochemical cycles, especially in gas exchange, in ice-covered seas because of the assumption that sea-ice acts as a barrier for atmosphere-ocean exchange. However, recent works have shown that sea ice and its snow cover play an active role in the exchange of gases between the ocean and atmosphere. In this paper, results obtained in my previous studies were reviewed.
• Helicopter-borne observations with portable microwave radiometer in the Southern Ocean and the Sea of Okhotsk

  Takeshi Tamura, Kay I. Ohshima, Jan L. Lieser, Takenobu Toyota, Kazutaka Tateyama, Daiki Nomura, Kazuki Nakata, Alexander D. Fraser, Peter W. Jansen, Kym B. Newbery, Robert A. Massom, Shuki Ushio

  ANNALS OF GLACIOLOGY 56 69 436 - 444 2015年 [査読有り][通常論文]
   

  Accurately measuring and monitoring the thickness distribution of thin ice is crucial for accurate estimation of ocean atmosphere heat fluxes and rates of ice production and salt flux in ice-affected oceans. Here we present results from helicopter-borne brightness temperature (TB) measurements in the Southern Ocean in October 2012 and in the Sea of Okhotsk in February 2009 carried out with a portable passive microwave (PMW) radiometer operating at a frequency of 36 GHz. The goal of these measurements is to aid evaluation of a satellite thin-ice thickness algorithm which uses data from the spaceborne Advanced Microwave Scanning Radiometer Earth Observing System AMSR-E) or the Advanced Microwave Scanning Radiometer-II (AMSR-II). AMSR-E and AMSR-II TB agree with the spatially collocated mean TB from the helicopter-borne measurements within the radiometers' precision. In the Sea of Okhotsk in February 2009, the AMSR-E 36 GHz TB values are closer to the mean than the modal TB values measured by the helicopter-borne radiometer. In an Antarctic coastal polynya in October 2012, the polarization ratio of 36 GHz vertical and horizontal TB is estimated to be 0.137 on average. Our measurements of the TB at 36 GHz over an iceberg tongue suggest a way to discriminate it from sea ice by its unique PMW signature.
• Variation of dimethylsulfide mixing ratio over the Southern Ocean from 36°S to 70°S

  Koga S, Nomura D, Wada M

  Polar Science, 8 (3), 306–313, 2014. 8 3 306 - 313 2014年09月 [査読有り][通常論文]
  
• 砕氷船を利用した海氷・海洋の生物地球化学研究

  野村 大樹, 西岡 純, 川合 美千代, 大木 淳之, 田村 岳史

  日本地球化学会年会要旨集 61 132 - 132 日本地球化学会 2014年 

  我が国におけるこれまでの海氷研究は、主に物理過程を明らかにすることに主眼が置かれ、海氷の物理的動態を実測や衛星観測、モデリングから明らかにする研究が精力的に進められてきた。一方で、海氷に関わる化学過程や生物過程に関しては、これまで十分な研究が展開されていなかった。海氷の生成が生み出す独特の海洋循環を介して、他海域の物質循環にまで多大な影響を与えているシステムの存在が指摘されており、これらのシステムを理解するためには、海氷の存在する時期から消失していくまでの詳細な時系列観測、ポリニヤにおける海氷の生成が起こっている現場での観測が欠かせない。また、地球規模で起こっている環境変動を理解するためには、通年観測する必要があり、海洋研究プラットフォームを生物地球化学分野で最大限活用すると同時に、厳冬期でも観測が続けられる本格的な観測研究用の砕氷船が欠かせないだろう。
• Winter-to-summer evolution of pCO(2) in surface water and air-sea CO2 flux in the seasonal ice zone of the Southern Ocean

  D. Nomura, H. Yoshikawa-Inoue, S. Kobayashi, S. Nakaoka, K. Nakata, G. Hashida

  BIOGEOSCIENCES 11 20 5749 - 5761 2014年 [査読有り][通常論文]
   

  Partial pressure of CO2 (pCO(2)) in surface water and vertical profiles of the carbonate system parameters were measured during austral summer in the Indian sector of the Southern Ocean (64-67 degrees S, 32-58 degrees E) in January 2006 to understand the CO2 dynamics of seawater in the seasonal ice zone. Surface-water pCO(2) ranged from 275 to 400 mu atm, and longitudinal variations reflected the dominant influence of water temperature and dilution by sea ice meltwater between 32 and 40 degrees E and biological productivity between 40 and 58 degrees E. Using carbonate system data from the temperature minimum layer (-1.9 degrees C < T <-1.5 degrees C, 34.2 < S < 34.5), we examined the winter-to-summer evolution of surface-water pCO(2) and the factors affecting it. Our results indicate that pCO(2) increased by as much as 32 mu atm, resulting mainly from the increase in water temperature. At the same time as changes in sea ice concentration and surface-water pCO(2), the air-sea CO2 flux, which consists of the exchange of CO2 between sea ice and atmosphere, changed from -1.1 to +0.9 mmol C m(-2) day(-1) between winter and summer. These results suggest that, for the atmosphere, the seasonal ice zone acts as a CO2 sink in winter and a temporary CO2 source in summer immediately after the retreat of sea ice. Subsequent biological productivity likely decreases surface-water pCO(2) and the air-sea CO2 flux becomes negative, such that in summer the study area is again a CO2 sink with respect to the atmosphere.
• Arctic and Antarctic sea ice acts as a sink for atmospheric CO2 during periods of snowmelt and surface flooding

  Daiki Nomura, Mats A. Granskog, Philipp Assmy, Daisuke Simizu, Gen Hashida

  Journal of Geophysical Research: Oceans 118 12 6511 - 6524 2013年12月 [査読有り]
  
• Characterization of ikaite (CaCO3·6H2O) crystals in first-year Arctic sea ice north of Svalbard

  Daiki Nomura, Philipp Assmy, Gernot Nehrke, Mats A. Granskog, Michael Fischer, Gerhard S. Dieckmann, Agneta Fransson, Yubin Hu, Bernhard Schnetger

  Annals of Glaciology 54 62 125 - 131 2013年 [査読有り][通常論文]
   

  We identified ikaite crystals (CaCO₃·6H₂O) and examined their shape and size distribution in first-year Arctic pack ice, overlying snow and slush layers during the spring melt onset north of Svalbard. Additional measurements of total alkalinity (TA) were made for melted snow and sea-ice samples. Ikaite crystals were mainly found in the bottom of the snowpack, in slush and the surface layers of the sea ice where the temperature was generally lower and salinity higher than in the ice below. Image analysis showed that ikaite crystals were characterized by a roughly elliptical shape and a maximum caliper diameter of 201.0±115.9 μm (n = 918). Since the ice-melting season had already started, ikaite crystals may already have begun to dissolve, which might explain the lack of a relationship between ikaite crystal size and sea-ice parameters (temperature, salinity, and thickness of snow and ice). Comparisons of salinity and TA profiles for melted ice samples suggest that the precipitation/dissolution of ikaite crystals occurred at the top of the sea ice and the bottom of the snowpack during ice formation/melting processes.
• An artificial pool experiment in Antarctic sea ice: effects of sea ice melting on physical and biogeochemical components of pool water

  Daiki Nomura, Daisuke Simizu, Suchana Chavanich, Hideo Shinagawa, Mitsuo Fukuchi

  ANTARCTIC SCIENCE 24 5 536 - 544 2012年10月 [査読有り][通常論文]
   

  We performed an artificial pool experiment in the Antarctic multi-year land-fast ice to examine and simulate the effect of sea ice melting on physical and biogeochemical components of the sea ice field. The input of snow and ice meltwater resulted in warmer, low salinity water at the surface of the pool and probably stratification of the less dense water. Current speed measurements also pointed to water stratification within the pool. Rapid phytoplankton growth in the pool resulted in drastic decreases in concentrations of dissolved inorganic carbon and nutrients (NO3- and Si(OH)(4)) in the surface waters of the pool, particularly depleted for NO3-. There was high correlation between variations of dissolved inorganic carbon and nutrient concentrations, but the apparent uptake ratios of these components deviated from that generally applied to marine phytoplankton. The sequence of changes in the physical and biogeochemical components of the pool water suggests that the onset of rapid phytoplankton growth was closely related to the water stratification, which provided stable conditions for phytoplankton bloom even though the supply of nutrients from under-ice water would have declined.
• Direct measurements of DMS flux from Antarctic fast sea ice to the atmosphere by a chamber technique

  Daiki Nomura, Seizi Koga, Nobue Kasamatsu, Hideo Shinagawa, Daisuke Simizu, Makoto Wada, Mitsuo Fukuchi

  Journal of Geophysical Research: Oceans 117 4 2012年 [査読有り][通常論文]
   

  We present the first direct measurements of dimethylsulfide (DMS) emissions from Antarctic sea ice to the atmosphere during the seasonal warming period obtained using a chamber technique. Estimated DMS fluxes measured over the snow and superimposed ice (ice formed by the freezing of snow meltwater) were from 0.1 to 0.3 μmol m-2 d-1. The DMS fluxes measured directly over the sea-ice slush layer after removal of the snow and superimposed ice, ranged from 0.1 to 5.3 μmol m-2 d-1, were large compared to those measured over the snow and superimposed ice. The DMS concentrations in slush water ranged from 1.0 to 103.7 nM. The DMS fluxes increased with increasing DMS concentrations in slush water. Our results indicate that the potential DMS flux measured over the slush layer occurred originally from the slush layer, and was dependent on the DMS concentrations in slush water. However, snow accumulation and the formation of superimposed ice over the slush layer significantly blocks the diffusion of DMS to the atmosphere, with the result that DMS tends to accumulate in the slush layer although the removal process of DMS by photolysis reaction can modify the DMS flux from the slush layer. Hence, the slush layer has the potential to release the DMS to the atmosphere and ocean when the snow and superimposed ice melts.
• Bromoform concentrations in slush-layer water in Antarctic fast ice

  Daiki Nomura, Atsushi Ooki, Daisuke Simizu, Mitsuo Fukuchi

  ANTARCTIC SCIENCE 23 6 623 - 628 2011年12月 [査読有り][通常論文]
   

  Bromoform concentrations in water of the slush layer that developed at the interface between snow and sea ice were measured during the seasonal warming in Lutzow-Holm Bay, East Antarctica. Mean bromoform concentration was 5.5 +/- 2.4 pmol l(-1), which was lower than that of the under-ice water (10.9 +/- 3.5 pmol l(-1)). Temporal decrease in bromoform concentrations and salinity with increasing temperature of the slush water suggest that the bromoform concentrations were reduced through dilution with meltwater input from the upper surface of sea ice. In contrast, bromoform concentrations in the under-ice water increased during this period while the salinity of the under-ice water decreased. It is speculated that the sea ice meltwater input contained high bromoform concentrations from the brine channels within the sea ice and from the bottom of the ice that were contributed to the increased bromoform concentrations in the under-ice water.
• Incorporation of nitrogen compounds into sea ice from atmospheric deposition

  Daiki Nomura, Andrew McMinn, Hiroshi Hattori, Shigeru Aoki, Mitsuo Fukuchi

  MARINE CHEMISTRY 127 1-4 90 - 99 2011年12月 [査読有り][通常論文]
   

  Temporal measurements of temperature, salinity, water-oxygen isotopic ratio and nutrient concentrations at Saroma-ko Lagoon, southern Sea of Okhotsk, were made in February-March 2008 to examine the processes by which nitrogen compounds from the atmosphere were incorporated via snowfall into sea ice. Granular ice made up more than half the ice thickness, and the mass fraction of snow in the snow-ice layer on top of the ice ranged from 0.8% to 46.9%. The high concentrations of NO(3)(-) + NO(2)(-) and NH(4)(+) observed in the snow and snow-ice throughout the study period were likely due to the proximity of the study site, in northern Japan, to the east coast of the Asian continent. Pollutants containing high NO(3)(-) and NH(4)(+) concentrations are transported from East Asia and deposited in snowfall over the sea ice in the southern part of the Sea of Okhotsk. Compared with NO(3)(-) + NO(2)(-) and NH(4)(+) concentrations, PO(4)(3-) concentrations in the snow and snow-ice were low. The strong correlation between the NO(3)(-) + NO(2)(-) and NH(4)(+) concentrations in the snow-ice and the mass fraction of snow indicates that the nitrogen compounds on top of the sea ice were controlled mainly by the snow contribution to the sea ice when snow-ice predominated. Our results indicate that chemical cycles in sea ice can be affected by polluted precipitation (snow) originating from a nonpolar sea. (C) 2011 Elsevier B.V. All rights reserved.
• DMSP and DMS in coastal fast ice and under-ice water of Lützow-Holm Bay, eastern Antarctica

  Nomura D, Kasamatsu N, Tateyama K, Kudoh S, Fukuchi M

  Continental Shelf Research, 31, pp1377–1383, 2011. 31 13 1377 - 1383 2011年09月 [査読有り][通常論文]
   

  The combined concentration of total dimethylsulfoniopropionate and dimethylsulfide (DMSP+DMS) were measured in Antarctic fast ice on the coast of Lutzow-Holm Bay, eastern Antarctica. High bulk-ice DMSP+DMS and chlorophyll a concentrations were found at the bottom of the sea ice, and these concentrations were higher than those in the under-ice water. The bulk-ice DMSP+DMS and chlorophyll a concentrations were highly correlated (r(2)=0.68, P < 0.001), suggesting that the high bulk-ice DMSP+DMS concentrations were caused mainly by the presence of algae assemblages in the ice. The calculated brine DMSP+DMS concentrations were as high as 1100 nM in the bottom ice layer, and the vertical profile patterns of brine DMSP+DMS concentrations were almost the same as for the bulk ice, mainly because of the small amount of variability in the vertical brine volume fraction. DMSP+DMS and chlorophyll a concentrations in the under-ice water increased, whereas the salinity of the under-ice water decreased, during the sampling period. These results reflect the supply of freshwater containing high levels of DMSP+DMS to the water just under the ice as the ice melted. These results suggest that sea-ice melting could be important to sulfur cycling in coastal ice-covered regions of the polar oceans. (C) 2011 Elsevier Ltd. All rights reserved.
• Biogeochemical properties of water in surface ponds on Antarctic fast ice and their relationship with underlying sea-ice properties

  Daiki Nomura, Daisuke Simizu, Hideo Shinagawa, Chinatsu Ouchida, Mitsuo Fukuchi

  JOURNAL OF GLACIOLOGY 57 205 848 - 856 2011年 [査読有り][通常論文]
   

  Surface ponds on Antarctic fast ice were examined by measuring temperature, salinity and concentrations of chlorophyll a (Chl-a), dissolved inorganic carbon (DIC) and nutrients (NO(3) + NO(2), PO(4), and SiO(2)) in the surface pond water and under-ice water. Sea-ice cores were also collected from the bottom of a surface pond (pond-ice core) and from a site away from the pond (bare-ice core). Time-series measurements of surface pond water temperature showed that it varied with solar radiation rather than with air temperature. Comparison of water properties between surface pond water and under-ice water suggested that DIC and nutrients were consumed by biological productivity during pond formation. Depth profiles of nutrient concentrations in the pond-ice core suggested the remineralization of organic matter at the bottom of the surface pond. The Chl-a concentration was lower at the bottom of the pond-ice core than in the bare-ice core, suggesting that surface pond formation reduces ice algae abundance in sea ice because meltwater flushes algae from the porous sea ice into the under-ice water.
• Flux of low salinity water from Aniva Bay (Sakhalin Island) to the southern Okhotsk Sea

  Sachiko Oguma, Tsuneo Ono, Yutaka W. Watanabe, Hiromi Kasai, Shuichi Watanabe, Daiki Nomura, Humio Mitsudera

  ESTUARINE COASTAL AND SHELF SCIENCE 91 1 24 - 32 2011年01月 [査読有り][通常論文]
   

  In this study, we examined the relationship between the low salinity water in the shelf region of the southern Okhotsk Sea which was seasonally sampled (0-200 m), and fluxes of low salinity water from Aniva Bay. To express the source of freshwater mixing in the surface layer, we applied normalized total alkalinity (NTA) and stable isotopes of seawater as chemical tracers. NTA-S diagrams indicate that NTA of low salinity water in the upper 30 m layer just off the Soya Warm Current is clearly higher than in the far offshore region in summer and autumn. Using NTA-S regression lines, we could deduce that the low salinity and high NTA water in the upper layer originates from Aniva Bay. For convenience, we defined this water as the Aniva Surface Water (ASW) with values S < 32, NTA > 2450 umol kg(-1). Formation and transport processes of ASW are discussed using historical data. The interaction between the maximum core of high NTA water on the bottom slope of eastern Aniva Bay and an anticyclonic eddy at the mouth of Aniva Bay are concluded to control ASW formation. Upwelling of the Cold Water Belt water at the tip of Cape Krillion is considered to cause ASW outflow from Aniva Bay. (C) 2010 Elsevier Ltd. All rights reserved.
• Report on a portable laboratory, made from a modified cargo container, aboard the RV Shirase during the 2009-2010 Antarctic cruise of the 51st Japanese Antarctic Research Expedition (JARE-51)

  Wada M, Koga S, Nomura D, Odate T, Fukuchi M

  Antarctic Record, 55, 3, 269–286, 2011. 55 3 271 - 278 国立極地研究所 2011年 [査読有り][通常論文]
   

  2009年に就航した新「しらせ」には,改造した20 ftコンテナを船上実験室として搭載するスペースが確保された.第51次日本南極地域観測隊では,このコンテナ実験室の内部に大気中の硫化ジメチル濃度を測定するためのプロトン移動反応質量分析計を収納し,観測を実施した.本稿では,コンテナ実験室の概要と今後改良すべき点等について報告する.
• Rapid physically driven inversion of the air-sea ice CO2 flux in the seasonal landfast ice off Barrow, Alaska after onset of surface melt

  Daiki Nomura, Hajo Eicken, Rolf Gradinger, Kunio Shirasawa

  CONTINENTAL SHELF RESEARCH 30 19 1998 - 2004 2010年11月 [査読有り][通常論文]
   

  The air-sea ice CO2 flux was measured over landfast sea ice in the Chukchi Sea, off Barrow, Alaska in late May 2008 with a chamber technique. The ice cover transitioned from a cold early spring to a warm late spring state, with an increase in air temperature and incipient surface melt. During melt, brine salinity and brine dissolved inorganic carbon concentration (DIC) decreased from 67.3 to 18.7 and 3977.6 to 1163.5 mu mol kg(-1), respectively. In contrast, the salinity and DIC of under-ice water at depths of 3 and 5 m below the ice surface remained almost constant with average values of 32.4 +/- 0.3 (standard deviation) and 2163.1 +/- 16.8 mu mol kg(-1), respectively. The air-sea ice CO2 flux decreased from +0.7 to -1.0 mmol m(-2) day(-1) (where a positive value indicates CO2 being released to the atmosphere from the ice surface). During this early to late spring transition, brought on by surface melt, sea ice shifted from a source to a sink for atmospheric CO2, with a rapid decrease of brine DIC likely associated with a decrease in the partial pressure of CO2 of brine from a supersaturated to an undersaturated state compared to the atmosphere. Formation of superimposed ice coincident with melt was not sufficient to shut down ice-air gas exchange. (C) 2010 Elsevier Ltd. All rights reserved.
• Nutrient distributions associated with snow and sediment-laden layers in sea ice of the southern Sea of Okhotsk

  Daiki Nomura, Jun Nishioka, Mats A. Granskog, Andreas Krell, Sumito Matoba, Takenobu Toyota, Hiroshi Hattori, Kunio Shirasawa

  MARINE CHEMISTRY 119 1-4 1 - 8 2010年04月 [査読有り][通常論文]
   

  Samples of first-year sea ice, snow and under-ice water were collected in the southern Sea of Okhotsk in mid-February 2007 and 2008 to elucidate the processes controlling nutrient concentrations in sea ice. Temperature, salinity, oxygen isotopic ratio (delta O-18) and inorganic nutrient concentrations (NO3, NH4, NO2, PO4 and SiO2) were measured. Sea ice was categorized into four types; snow-ice, frazil ice, columnar ice and a mixture of granular and columnar ice, based on delta O-18 composition and ice texture. Frazil ice dominated the total ice thickness (52.8%), and columnar ice was sandwiched between frazil ice layers, indicating dynamic ice-growth processes such as rafting and ridging. Furthermore, the ice was banded by layers of particulate materials (sediment layers), which were frequently encountered during cruises. High NO3 and NH4 concentrations were found in snow and snow-ice implying that these were supplied from the atmosphere with snowfall and incorporated into the sea ice through snow-ice formation. In the sediment-laden layers, which were categorized as frazil ice, NO2, PO4 and SiO2 concentrations were highest of all the ice types and considerably enriched compared to parent seawater, suggesting the remineralization of the particulate organic matter. On the other hand, NO3 concentrations in sediment layers were low (depleted), leading to extremely low N (NO3 + NH4 + NO2): P ratios in sediment layers, from 0.2 to 0.8, with respect to that of under-ice water or Redfield ratio. These results suggest that in part of sediment-laden layers fixed-nitrogen was removed partially as molecular nitrogen (N-2) from the sea ice environment by anaerobic nitrate reduction processes (denitrification) by denitrifying bacteria while adding phosphate from associated remineralization of organic phosphorus. The effect of melting of snow and sea ice is dilution for salinity, NO3 and SiO2, no change in NO2 and PO4, and a minor enrichment for NH4 in the mixed layer in spring and early summer. This suggests that snow/ice meltwater with different nutrient ratios than in under-ice water/Redfield ratio is supplied to under-ice water during melt season in April/May in southern Sea of Okhotsk. However, the impact of sediment-laden sea ice cannot be assessed at this point. (C) 2009 Elsevier B.V. All rights reserved.
• Effects of snow, snowmelting and refreezing processes on air–sea-ice CO2 flux

  Nomura D, Yoshikawa-Inoue H, Toyota T, Shirasawa K

  Journal of Glaciology, 56, 196, pp262–270, 2010. 56 196 262 - 270 2010年 [査読有り][通常論文]
   

  The air-sea-ice CO2 flux was measured in the ice-covered Saroma-ko, a lagoon on the northeastern coast of Hokkaido, Japan, using a chamber technique. The air-sea-ice CO2 flux ranged from -1.8 to +0.5 mg C m(-2) h(-1) (where negative values indicate a sink for atmospheric CO2). The partial pressure of CO2 (pCO(2)) in the brine of sea ice was substantially lower than that of the atmosphere, primarily because of the influence of the under-ice plume from the Saromabetsu river located in the southeastern part of the lagoon. This suggests that the brine had the ability to take up atmospheric CO2 into the sea ice. However, the snow deposited over the sea ice and the superimposed ice that formed from snowmelting and refreezing partially blocked CO2 diffusion, acting as an impermeable medium for CO2 transfer. Our results suggest that the air-sea-ice CO2 flux was dependent not only on the difference in pCO(2) between the brine and the overlying air, but also on the status of the ice surface. These results provide the necessary evidence for evaluation of the gas exchange processes in ice-covered seas.
• Biogeochemical Properties of Sea Ice

  McMinn A, Gradinger R, Nomura D

  Field Techniques for Sea Ice Research, pp259–282, 2009. 2009年 [査読無し][通常論文]
  
• Transport of chemical components in sea ice and under-ice water during melting in the seasonally ice-covered Saroma-ko Lagoon, Hokkaido, Japan

  Daiki Nomura, Toru Takatsuka, Masao Ishikawa, Toshiyuki Kawamura, Kunio Shirasawa, Hisayuki Yoshikawa-Inoue

  ESTUARINE COASTAL AND SHELF SCIENCE 81 2 201 - 209 2009年01月 [査読有り][通常論文]
   

  Physico-chemical properties in the brine and under-ice water were measured in Saroma-ko Lagoon on the northeastern coast of Hokkaido, Japan, which is connected to the Sea of Okhotsk, during the period from mid-February through mid-March 2006. The brine within brine channels of the sea ice was collected with a new sampling method examined in this study. Salinity, dissolved inorganic carbon (DIC), total alkalinity (TA), dissolved oxygen (DO), nutrients and oxygen isotopic ratio (8180) contained in the brine within brine channels of the sea ice and in the under-ice water varied largely in both time and space during the ice melt period, when discharge from Saromabetsu River located on the southeast of the lagoon increased markedly due to the onset of snow melting. The under-ice plume expands as far as 4.5 km from the river mouth at mid-March 2006, transporting chemical components supplied from the river into the lagoon. The under-ice river water was likely transported into the sea ice through well-developed brine channels in the sea ice due to upward flushing of water through brine channels occurred by loading of snowfalls deposited over the sea ice. These results suggest that the river water plume plays an important role in supplying chemical components into the sea ice, which may be a key process influencing the biogeochemical cycle in the seasonally ice-covered Saroma-ko Lagoon. (C) 2008 Elsevier Ltd. All rights reserved.
• The effect of sea-ice growth on air-sea CO2 flux in a tank experiment

  Daiki Nomura, Hisayuki Yoshikawa-Inoue, Takenobu Toyota

  TELLUS SERIES B-CHEMICAL AND PHYSICAL METEOROLOGY 58 5 418 - 426 2006年11月 [査読有り][通常論文]
   

  In order to clarify the CO2 exchange between the seawater and the overlying air during the sea-ice formation, we have carried out tank experiments in a low-temperature room. CO2 concentration above the sea-ice began to increase since the beginning of the sea-ice formation, and increased at larger rates with time and the decrease in air temperature. This increase of CO2 concentration in air was mainly caused by the increase in dissolved inorganic carbon concentration in the brine of the upper part of sea-ice, changes in CO2 solubility and dissociation constants of carbonic acid. The CO2 flux increased logarithmically with time, and reached a level of 2 x 10(-4) to 5 x 10(-4) g-C m(-2) hr(-1) at 50 mm ice thickness. We found that the CO2 flux was correlated well with the salinity and negatively with the volume of the brine in the upper part of the sea-ice. These suggested the larger role of the difference in partial pressure of CO2 between brine and air as compared to that of competitive change in the brine volume. Present results suggest the necessity to examine the CO2 exchange between the seawater and air in seasonal sea-ice areas.

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受賞

• 2014年 日本海洋学会 岡田賞
  

共同研究・競争的資金等の研究課題

• 東南極における氷床－海氷－海洋システムの地域特性の解明 研究代表者 田村岳史 研究期間 (年度) 2021–2026 研究種目 基盤研究(A)

  日本学術振興会：科学研究費助成事業

  研究期間 : 2021年 -2026年03月 

  代表者 : 田村 岳史, 草原 和弥, 溝端 浩平, 平野 大輔, 野村 大樹, 巻 俊宏, 渡辺 豊

   

  白瀬氷河底面融解量と外洋からの熱供給との比較 白瀬氷河が存在するリュツォ・ホルム湾で取得した海洋観測データの解析から明らかにした白瀬氷河―海洋相互作用に関する研究結果を、海洋―海氷―棚氷結合モデルによる実験結果と比較・統合し、顕著な季節変動を伴う年間を通じた白瀬氷河舌の底面融解プロセスを明らかにした。海洋―海氷―棚氷結合モデルによる実験結果からは、中層での海流の変動が、沖合の暖水のLH湾湾内への流入の変動の決め手となっている事が示唆された。さらにこの数値モデルの結果からは、LH湾で卓越する存在である沿岸定着氷の存在が、大気海洋間の熱交換を遮断して海氷生成を抑制し、これが沖合から白瀬氷河への暖水流入をより強くする（又は暖かいままにしてたどり着く）要因を作っている事が明らかになった。衛星観測、海洋観測、測地観測、数値モデル結果は全て、白瀬氷河の高い底面融解率を示している。 ケープダンレー周辺域での海氷生産と外洋からの熱供給との比較 ケープダンレー周辺域において、顕著な海氷後退が海面での熱貯留を増やし、東風によりアメリ―棚氷下へ押し込まれると同時に棚氷底面を融解させて、ケープダンレー沖の暖水化・淡水化をもたらす一連の過程が現場観測により捉えられた。このケープダンレーからの底層水流出を数値実験で再現するうえで、観測に基づく詳細な現実地形を考慮することが、流出量の絶対値に大きく影響することが明らかになった。 このように、交付申請書に記載した「研究の目的」及び「研究実施計画」について、上記のように直接的に研究目的に対して成果を上げる事となった。
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  北海道大学低温科学研究所：

  研究期間 : 2024年04月 -2025年03月 

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• 環境DNAで北極海の海氷下の魚を探る

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• 海氷表面に見られる有機臭素ガスの高濃度現象―低温化学反応チャンバー実験による検証 研究代表者 野村大樹 研究期間 (年度) 2020 – 2022 研究種目 基盤研究(B)

  日本学術振興会：科学研究費助成事業

  研究期間 : 2020年 -2023年03月 

  代表者 : 野村 大樹, 薮下 彰啓, 山下 洋平, 大木 淳之

   

  高緯度海域に分布する海氷は、地球規模の気候変動を制御する要因として大きな役割を担っている。従来、海氷は、物質循環の観点において大気と海洋間の「障壁」として認識されてきた。しかし、実際、海氷表面では、結氷による濃縮効果によって溶存物質が高濃度化し、大気に対して放出源になることが予想される。ただ、極域の厳しい環境での観測の難しさにより、海氷表面での「低温化学」に関する反応機構の解明に至っていない。本研究では、自然界で起こる結氷現象を室内でのチャンバー実験で再現し、有機臭素ガス、特にブロモホルムに関して、海氷表面での化学反応機構・大気への放出過程を明らかにすることが目的である。本課題は、極域大気中オゾン濃度の急激な減少を招く有機臭素ガスの発生源が特定されていないことから設定した。本研究で提唱する海氷表面でのブロモホルム生成は、有機臭素ガスの大気への新たな発生源の提案となり、長年謎とされてきた大気中オゾン消失現象の原因解明に一石を投じることとなる。しかし、これまでの応募者らによる観測事実と低温環境での化学反応の新たな知見により、反応仮説を提唱するに至ったが、反応機構は検証されていない。そこで本年度は、チャンバー実験を実施し、本研究の解明に向けてのデータの採取を行った。具体的には、購入したチャンバーを利用した化学反応実験、また、室内での結氷および積雪を再現し、ブロモホルム生成に関する室内実験を実施した。また、これまでの観測データの解析を実施した。これらの解析を実施することにより、当初の目的に向けて順調に研究が進んでいる状況にある。
• イメージングとAIで紐解く南大洋の炭素循環 研究代表者 真壁竜介 研究期間（年度）2023-2028 研究種目 CREST

  研究期間 : 2023年
• 海氷-海洋境界層理論に基づく海氷モニタリング技術開発と自動観測ネットワークの構築 研究代表者 川口悠介 研究期間 (年度) 2022-2025 研究種目 基盤研究(B)

  研究期間 : 2022年
• 海の暗い所で珪藻が栄養塩を消費する事実－生存戦略の仮説を提唱－研究代表者 大木淳之 研究期間 (年度) 2021–2025 研究種目 挑戦的研究（萌芽）

  研究期間 : 2022年
• 日独共同観測による「北極の湿潤化」の追究 研究代表者 猪上 淳 研究期間 (年度) 2018 – 2020 研究種目 国際共同研究加速基金(国際共同研究強化(B))

  研究期間 : 2018年
• 海洋炭酸系物質の時空間高解像度マッピング技術の南大洋への展開 研究代表者 渡辺 豊 研究期間 (年度) 2018 – 2020 研究種目 基盤研究(A)

  研究期間 : 2018年
• 北極漂流横断観測による「新しい北極海」の探究 研究代表者 猪上 淳 研究期間 (年度) 2018 – 2021 研究種目 基盤研究(A)

  研究期間 : 2018年
• 極域雪氷の融解現象が海洋表層の二酸化炭素濃度と大気との気体交換過程に与える影響 研究代表者 野村 大樹 研究期間 (年度) 2017 – 2019 研究種目 若手研究(A)

  研究期間 : 2017年
• 海洋沿岸におけるヨウ素循環の解明－有機物分解に伴うヨウ素の化学形態変化－ 研究代表者 大木 淳之 研究期間 (年度) 2016 – 2020 研究種目 基盤研究(B)

  研究期間 : 2016年
• 氷上現場観測による冬季海氷域の大気－海氷－海洋間の炭素輸送プロセスの解明

  日本学術振興会：科学研究費助成事業

  研究期間 : 2012年04月 -2015年03月 

  代表者 : 野村 大樹

   

  本研究の目的は、冬季海氷域の大気－海氷－海洋間の炭素および物質輸送プロセスを明らかにすることである。これまでの調査では、気候条件の厳しさやプラットフォームの整備が課題となり、冬季の氷上野外観測は実現困難であった。そこで本研究では、冬季の観測を集中的に実施した。特に今年度は、
  (1) アルフレッドウェゲナー極地海洋研究所（ドイツ）が所有する砕氷船ポーラシュテルンを用いた厳冬期南極海（2013年6-8月）で採取したサンプルの分析作業を実施した。分析結果を組み合わせ、大気―海氷間の二酸化炭素とブロモホルム交換量の評価／変動要因を明らかにした。上記分析で得られた結果をまとめ、国際学会および国内学会で成果発表した。現在、国際査読誌への投稿に向けて執筆作業を進めている。
  (2) ノルウェー極地研究所（ノルウェー）が所有する砕氷船ランセを用いた厳冬期北極海航海（2015年2-3月）に参加し、氷上観測を実施した。観測サイトでは、海氷上積雪、海氷、海氷下海水を採取した。また、大気―海氷間の二酸化炭素とブロモホルム交換量の測定を実施した。特に、大気―海氷間の二酸化炭素交換量の測定では、気温による交換量の変化、積雪による交換量の抑制に関する貴重なデータを取得した。今後、各研究機関での分析、データ解析をする。そして、分析結果、取得データ解析をまとめ、国際学会および国内学会で成果発表する。最終的に（１）（２）を組み合わせ、冬季海氷域の大気－海氷－海洋間の炭素および物質輸送プロセスを明らかにする。
• 海洋の炭酸系物質の準リアルタイムな時空間高解像度マッピングの展開に関する研究 研究代表者 渡辺 豊 研究期間 (年度) 2015 – 2017 研究種目 基盤研究(B)

  研究期間 : 2015年
• 海氷内部における炭酸カルシウム結晶の生成メカニズムの解明 研究代表者 野村 大樹 研究期間 (年度) 2015 – 2016 研究種目 若手研究(B)

  研究期間 : 2015年
• 海氷融解による生態系の変化が物質循環に与える影響ー豪州砕氷船による国際南極観測ー 研究代表者 飯田 高大 研究期間 (年度) 2015 – 2017 研究種目 基盤研究(B)

  研究期間 : 2015年
• 南極海における海氷の生成と融解が大気-海洋間の二酸化炭素交換過程に及ぼす影響 研究代表者 野村 大樹 研究期間 (年度) 2009 – 2010 研究種目 研究活動スタート支援

  日本学術振興会：科学研究費助成事業

  研究期間 : 2009年 -2010年 

  代表者 : 野村 大樹

   

  南極海における海氷の生成と融解が大気-海洋間の二酸化炭素(CO_2)交換過程に及ぼす影響を定量的に評価するため、2009年11月から2010年3月に砕氷艦『新しらせ』を用い、南極海季節海氷域で海氷/海洋観測を実施した。本観測データは、厳しい気候条件により、殆ど観測例がない南極海の海氷域の炭素循環についての有益なデータを提示する事が可能となった。本研究で得られた結果は、南極海の物質循環に関する将来予測研究の進展に大きく貢献できると考えられる。
• 海氷生成と融解に伴う大気への二酸化炭素放出・吸収に関する研究

  日本学術振興会：科学研究費助成事業

  研究期間 : 2007年 -2008年 

  代表者 : 野村 大樹

   

  『研究の目的』は、季節海氷域での氷上現場観測より海氷の生成・融解に伴う大気-海洋間のCO_2交換を支配する要因を明らかにし、季節海氷域が炭素循環に果たす役割を評価することである。本年度の『研究実施計画』は、平成19年度に実施した観測・分析(1、季節海氷域での大気-海氷間の各種気体交換量の解明、2、海氷中ブライン・海氷下海水のサンプリング及び各種気体の分析)の結果をまとめ、学会発表、国際雑誌に投稿することである。以下に本年度に国際雑誌に投稿済み(2報)、受理済み(1報)の論文の内容を示す。 1.季節海氷域での大気-海氷間の各種気体交換量の解明(国際雑誌投稿中) 2006、2008年2-3月にオホーツク沿岸サロマ湖で大気-海氷間のCO_2フラックスを測定した。大気-海氷間のCO_2フラックスは、-2.3から+0.5mg-Cm^<-2>hour^<-1>となった。観測期間中、積雪及び海水表面の融解と再凍結によって出来た氷に海氷表面が覆われる時期があった。その結果、ブライン・チャネルのような気体交換を可能とする場所が、海氷表面での融解と再凍結によって塞がれたため、大気から海氷へのCO_2吸収が制限された。大気-海氷中ブライン間のpCO_2差にだけでなく、海氷表面の特性も、大気-海氷間のCO_2フラックスを決定する重要な要因であることが示された。 2.海氷中ブライン・海氷下海水のサンプリング及び各種気体の分析(国際雑誌受理済) 海氷融解期におけるブライン・海氷下海水の化学特性変化を解明するため、2006、2008年2月-3月はじめにオホーツク海沿岸サロマ湖東部で氷上現場観測を行った。日中の気温の上昇に伴い、海氷上部または内部での融解や、河川水流入量増加によりブライン・表層水の塩分は大幅に減少した。中層・深層では、ほぼ一定の値となった。DO、TA、栄養塩各種は、塩分と同様にブライン・表層水で大きく変化した。観測点がサロマベツ川に近づくほど、その値は河川のものと近くなった。これは、主に河川水量増加によってSt.Main表層水の値が変化したことを示唆している。また、海氷から融解水が海氷下に流出する際、入れ替わりに海氷直下の海水をブライン・チャネル内に取り込むためにブラインの各成分値も大きく変化した。

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