研究者データベース

平野 大輔(ヒラノ ダイスケ)
低温科学研究所 水・物質循環部門
助教

基本情報

所属

  • 低温科学研究所 水・物質循環部門

職名

  • 助教

学位

  • 博士(海洋科学)(東京海洋大学)

ホームページURL

科研費研究者番号

  • 30790977

J-Global ID

研究キーワード

  • 極域海洋学   沿岸ポリニヤ   氷床・海洋・海氷システム   南大洋   北極海   乱流   海洋物理学   

研究分野

  • 自然科学一般 / 大気水圏科学 / 海洋物理学

職歴

  • 2017年04月 - 現在 北海道大学 北極域研究センター(兼務)
  • 2016年10月 - 現在 北海道大学 低温科学研究所 水・物質循環部門 助教
  • 2016年04月 - 2016年09月 国立極地研究所 気水圏研究グループ 特任研究員
  • 2012年04月 - 2016年03月 国立極地研究所 国際北極環境研究センター 特任研究員
  • 2011年04月 - 2012年03月 水産総合研究センター 国際水産資源研究所 研究支援職員
  • 2010年10月 - 2011年03月 東京海洋大学 観測支援センター 博士研究員

学歴

  • 2007年04月 - 2010年09月   東京海洋大学大学院 海洋科学技術研究科 応用環境システム学専攻 博士課程
  • 2004年04月 - 2006年03月   東京海洋大学大学院   海洋科学技術研究科   海洋環境保全学専攻 修士課程
  • 2000年04月 - 2004年03月   東京水産大学   水産学部   海洋環境学科

所属学協会

  • American Geophysical Union   日本海洋学会   

研究活動情報

論文

  • S. Aoki, K. Yamazaki, D. Hirano, K. Katsumata, K. Shimada, Y. Kitade, H. Sasaki, H. Murase
    Scientific Reports 10 1 14415 - 14415 2020年12月01日 [査読有り][通常論文]
     
    © 2020, The Author(s). The Antarctic continental margin supplies the densest bottom water to the global abyss. From the late twentieth century, an acceleration in the long-term freshening of Antarctic Bottom Waters (AABW) has been detected in the Australian-Antarctic Basin. Our latest hydrographic observations reveal that, in the late 2010s, the freshening trend has reversed broadly over the continental slope. Near-bottom salinities in 2018–2019 were higher than during 2011–2015. Along 170° E, the salinity increase between 2011 and 2018 was greater than that observed in the west. The layer thickness of the densest AABW increased during the 2010s, suggesting that the Ross Sea Bottom Water intensification was a major source of the salinity increase. Freshwater content on the continental slope decreased at a rate of 58 ± 37 Gt/a in the near-bottom layer. The decadal change is very likely due to changes in Ross Sea shelf water attributable to a decrease in meltwater from West Antarctic ice shelves for the corresponding period.
  • Daisuke Hirano, Takeshi Tamura, Kazuya Kusahara, Kay I. Ohshima, Keith W. Nicholls, Shuki Ushio, Daisuke Simizu, Kazuya Ono, Masakazu Fujii, Yoshifumi Nogi, Shigeru Aoki
    Nature Communications 11 1 4221 - 4221 2020年12月01日 [査読有り][通常論文]
     
    © 2020, The Author(s). Mass loss from the Antarctic ice sheet, Earth’s largest freshwater reservoir, results directly in global sea-level rise and Southern Ocean freshening. Observational and modeling studies have demonstrated that ice shelf basal melting, resulting from the inflow of warm water onto the Antarctic continental shelf, plays a key role in the ice sheet’s mass balance. In recent decades, warm ocean-cryosphere interaction in the Amundsen and Bellingshausen seas has received a great deal of attention. However, except for Totten Ice Shelf, East Antarctic ice shelves typically have cold ice cavities with low basal melt rates. Here we present direct observational evidence of high basal melt rates (7–16 m yr−1) beneath an East Antarctic ice shelf, Shirase Glacier Tongue, driven by southward-flowing warm water guided by a deep continuous trough extending to the continental slope. The strength of the alongshore wind controls the thickness of the inflowing warm water layer and the rate of basal melting.
  • Shigeru Aoki, Kazuya Ono, Daisuke Hirano, Takeshi Tamura
    Journal of Oceanography 76 5 365 - 372 2020年10月01日 [査読有り][通常論文]
     
    © 2020, The Oceanographic Society of Japan and Springer Nature Singapore Pte Ltd. Antarctic coastal polynyas provide extremely dense water to the global abyss, but the dense water formation process has been poorly monitored in winter. This study developed a new tethered profiler to realize time-series observations of the water column in the Cape Darnley Polynya, East Antarctica. The system successfully obtained temperature and salinity profiles at 10-day intervals from March to November 2017. From March to April, significant cooling and vertical mixing started, while stratification collapsed. Salinity increased rapidly from April to late-May and then gradually increased until October. Salinity development was largely consistent with the cumulative salt increase due to sea-ice production at the initial stage, but not at latter stages, indicating the influence of cross-shelf exchange. These results highlighted the potential of the measurement platform to fill the remaining gap in the global ocean monitoring network.
  • Kan Murakami, Daiki Nomura, Gen Hashida, Shin ichiro Nakaoka, Yujiro Kitade, Daisuke Hirano, Toru Hirawake, Kay I. Ohshima
    Marine Chemistry 225 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.
  • S. Aoki, K. Katsumata, M. Hamaguchi, A. Noda, Y. Kitade, K. Shimada, D. Hirano, D. Simizu, Y. Aoyama, K. Doi, Y. Nogi
    Journal of Geophysical Research: Oceans 125 8 e2020JC016374  2020年08月01日 [査読有り][通常論文]
     
    © 2020. American Geophysical Union. All Rights Reserved. Recently, a source of Antarctic Bottom Water (AABW) was identified off Cape Darnley at the eastern end of the Weddell-Enderby Basin. However, the behavior and long-term variability of Cape Darnley Bottom Water (CDBW) are not clearly understood. Hydrographic observations from 1974 to 2016 were compared, and a decade-long bottom temperature record was analyzed to clarify multidecadal changes in the CDBW in this region and its downstream influences. In the Cooperation Sea, CDBW spread northwestward with its deepest part reaching to approximately 4,900 dbar. CDBW freshening of 0.001–0.003 decade−1 was revealed. In the Cosmonaut Sea, long-term AABW warming of approximately 0.01–0.03°C decade−1 was prominent in the deep basin, while freshening was detected on the upper continental slope. Spatial patterns suggest that an interbasin deep transport of excess freshwater is carried by CDBW and fed into the Weddell Gyre, which might act as an abyssal freshwater buffer.
  • 菅沼 悠介, 石輪 健樹, 川又 基人, 奥野 淳一, 香月 興太, 板木 拓也, 関 宰, 金田 平太郎, 松井 浩紀, 羽田 裕貴, 藤井 昌和, 平野 大輔
    地学雑誌 129 5 591 - 610 東京地学協会 2020年
  • Masato Ito, Kay I. Ohshima, Yasushi Fukamachi, Daisuke Hirano, Andrew R. Mahoney, Joshua Jones, Toru Takatsuka, Hajo Eicken
    Journal of Geophysical Research: Oceans 124 12 8701 - 8719 2019年12月01日 [査読有り][通常論文]
     
    ©2019. American Geophysical Union. All Rights Reserved. Arctic sea ice incorporates and transports sediment, releasing it back into the water column during the melting season. This process constitutes an important aspect of marine sediment transport and biogeochemical cycling. Sediment incorporation into sea ice is considered to occur mainly through underwater interaction between frazil ice and resuspended sediment, referred to as suspension freezing. However, harsh environmental conditions have greatly limited field observations of this phenomenon. Analysis of mooring data from a coastal polynya in the northeastern Chukchi Sea, in conjunction with coastal ice radar and meteorological data, indicates that suspension freezing is a key mechanism for sediment entrainment into sea ice. During polynya episodes, acoustic backscatter data obtained by an Acoustic Doppler Current Profiler showed the presence of frazil ice from the surface down to 20- to 25-m depth, coinciding with in situ and potential supercooling. Underwater frazil ice persisted over 1 week under windy, turbulent water column conditions. A combination of the turbidity and Acoustic Doppler Current Profiler backscatter data revealed upward sediment dispersion associated with strong currents during the polynya episodes. The fact that frazil ice and resuspended sediment were detected at the same depth and time strongly suggests the interaction between ice crystals and sediment particles, that is, suspension freezing.
  • Daisuke Hirano, Yasushi Fukamachi, Kay I. Ohshima, Eiji Watanabe, Andrew R. Mahoney, Hajo Eicken, Motoyo Itoh, Daisuke Simizu, Katsushi Iwamoto, Joshua Jones, Toru Takatsuka, Takashi Kikuchi, Takeshi Tamura
    Journal of Geophysical Research: Oceans 123 8 5688 - 5705 2018年08月 [査読有り][通常論文]
     
    ©2018. American Geophysical Union. All Rights Reserved. Water properties and formation processes of Alaskan Coastal Winter Water (ACWW) over the eastern Chukchi shelf along the Alaska coast, the so-called Barrow Canyon pathway, are examined using data from moorings, atmospheric reanalysis, satellite-derived sea-ice production (SIP), and a numerical tracer experiment. Along this pathway, Pacific Winter Water (PWW) can be modified to produce ACWW through SIP accompanied by production of cold, saline polynya water in the coastal polynyas, upwelling of warm Atlantic Water (AW), and mixing processes on the shelf. Three different types of ACWW are formed: (i) a mixture of AW and PWW, (ii) a mixture of AW and polynya water, and (iii) hypersaline polynya water. The northeasterly winds, correlated with the north-south atmospheric pressure gradient between Beaufort High and Aleutian Low, are common triggers of polynya SIP episodes and AW upwelling in the Barrow Coastal Polynya (BCP). Due to the dual impact of northeasterly winds, PWW modification processes in the BCP are more complicated than what occurs elsewhere in the Chukchi Polynya. The impact of AW upwelling on the ACWW formation is most prominent in the BCP, usually centered along the coast. All types of ACWW are thought to be basically transported westward or northwestward with the Chukchi slope current and/or Beaufort Gyre and finally contribute to maintenance of the lower halocline layer especially over the Chukchi Borderland, Northwind Ridge, and southern Canada Basin. Even in the Pacific sector of the Arctic Ocean, ACWW properties are strongly influenced by both Atlantic-origin and Pacific-origin waters.
  • Makabe R, Tamura T, Tanimura A, Shimada K, Hirano D, Fukuchi M, Hashihama F
    Polar Science 12 25 - 33 2017年06月 [査読有り][通常論文]
     
    © 2016 Elsevier B.V. and NIPR To elucidate spatial differences in mesozooplankton community structure in local scale, vertical hauls using a 60-μm mesh closing net were carried out off Lützow-Holm Bay in January 2008. All of the zooplankton samples collected from three layers (0–100, 100–200, and 200–500 m) at seven stations were dominated by Oithona spp., Oncaea spp., Ctenocalanus citer, Microcalanus pygmaeus, and copepod nauplii. The cluster analysis of mesozooplankton abundances showed three distinct groups according to sampling depth, which appeared to be due to the preferential vertical distribution of dominant copepods. The other cluster analysis on integrated abundance upper 500 m revealed that mesozooplankton community structures at stations located on the western and eastern edges of the observation area (Cluster A) differed from those at the central stations (Cluster B). Abundance of copepod nauplii, Oithona spp., and C. citer differed between Clusters A and B, which was likely caused by differences in recruitment and early development in the dominant copepods, being associated with the timing and duration of ice edge blooms. This suggests that such heterogeneity in abundance and recruitment/development of dominant taxa was likely caused by local heterogeneity in sea ice dynamics. This may affect our understanding of zooplankton distribution.
  • Daisuke Hirano, Yasushi Fukamachi, Eiji Watanabe, Kay I. Ohshima, Katsushi Iwamoto, Andrew R. Mahoney, Hajo Eicken, Daisuke Simizu, Takeshi Tamura
    Journal of Geophysical Research: Oceans 121 1 980 - 997 2016年01月01日 [査読有り][通常論文]
     
    © 2016. American Geophysical Union. All Rights Reserved. The nature of the Barrow Coastal Polynya (BCP), which forms episodically off the Alaska coast in winter, is examined using mooring data, atmospheric reanalysis data, and satellite-derived sea-ice concentration and production data. We focus on oceanographic conditions such as water mass distribution and ocean current structure beneath the BCP. Two moorings were deployed off Barrow, Alaska in the northeastern Chukchi Sea from August 2009 to July 2010. For sea-ice season from December to May, a characteristic sequence of five events associated with the BCP has been identified; (1) dominant northeasterly wind parallel to the Barrow Canyon, with an offshore component off Barrow, (2) high sea-ice production, (3) upwelling of warm and saline Atlantic Water beneath the BCP, (4) strong up-canyon shear flow associated with displaced density surfaces due to the upwelling, and (5) sudden suppression of ice growth. A baroclinic current structure, established after the upwelling, caused enhanced vertical shear and corresponding vertical mixing. The mixing event and open water formation occurred simultaneously, once sea-ice production had stopped. Thus, mixing events accompanied by ocean heat flux from the upwelled warm water into the surface layer played an important role in formation/maintenance of the open water area (i.e., sensible heat polynya). The transition from a latent to a sensible heat polynya is well reproduced by a high-resolution pan-Arctic ice-ocean model. We propose that the BCP, previously considered to be a latent heat polynya, is a wind-driven hybrid latent and sensible heat polynya, with both features caused by the same northeasterly wind.
  • Daisuke Hirano, Yujiro Kitade, Kay I. Ohshima, Yasushi Fukamachi
    Journal of Geophysical Research: Oceans 120 2 910 - 922 2015年02月17日 [査読有り][通常論文]
     
    © 2014. American Geophysical Union. All Rights Reserved. The mixing process associated with modified Shelf Water (mSW) overflows that eventually mix to form Cape Darnley Bottom Water (CDBW) was investigated by hydrographic and microstructure observations off the Cape Darnley Polynya (CDP), East Antarctica, in January 2009. Closely spaced microstructure observations revealed that mSW properties varied considerably within a distance of ∼4 km across the shelf edge. Near the bottom, the rate of turbulent kinetic energy dissipation was enhanced to values greater than 10-7 W kg-1, and the vertical scale of the bottom boundary layer (BBL) was on the order of 10 m. The observed BBL around the shelf edge was characterized by strong vertical mixing with turbulent eddy diffusivities of ∼O(10-3-10-2) m2 s-1. A geostrophically balanced density current, which resulted from the presence of mSW over the continental shelf, is considered the primary energy source for the turbulent mixing in the BBL. This turbulent mixing transforms the overflowing mSW through mixing with ambient water masses, specifically with the overlying modified Circumpolar Deep Water. The BBL is also thought to partly contribute to the gradual descent of mSW down the continental slope through bottom Ekman transport. We conclude that turbulent mixing, primarily caused by a density current, plays an important role in CDBW formation, by modifying the mSW overflowing from the CDP.
  • Kay I. Ohshima, Yasushi Fukamachi, Guy D. Williams, Sohey Nihashi, Fabien Roquet, Yujiro Kitade, Takeshi Tamura, Daisuke Hirano, Laura Herraiz-Borreguero, Iain Field, Mark Hindell, Shigeru Aoki, Masaaki Wakatsuchi
    Nature Geoscience 6 3 235 - 240 2013年03月 [査読有り][通常論文]
     
    The formation of Antarctic Bottom Water-the cold, dense water that occupies the abyssal layer of the global ocean-is a key process in global ocean circulation. This water mass is formed as dense shelf water sinks to depth. Three regions around Antarctica where this process takes place have been previously documented. The presence of another source has been identified in hydrographic and tracer data, although the site of formation is not well constrained. Here we document the formation of dense shelf water in the Cape Darnley polynya (65°-69°E) and its subsequent transformation into bottom water using data from moorings and instrumented elephant seals (Mirounga leonina). Unlike the previously identified sources of Antarctic Bottom Water, which require the presence of an ice shelf or a large storage volume, bottom water production at the Cape Darnley polynya is driven primarily by the flux of salt released by sea-ice formation. We estimate that about 0.3-0.7 × 106 m3 s-1 of dense shelf water produced by the Cape Darnley polynya is transformed into Antarctic Bottom Water. The transformation of this water mass, which we term Cape Darnley Bottom Water, accounts for 6-13% of the circumpolar total. Copyright © 2013 Macmillan Publishers Limited.
  • Kazuo Amakasu, Atsushi Ono, Daisuke Hirano, Masato Moteki, Takashi Ishimaru
    Polar Science 5 2 187 - 194 2011年08月 [査読有り][通常論文]
     
    From January to February 2008 the training research vessel TRV Umitaka Maru conducted a comprehensive oceanographic survey of the waters around the 140°E meridian off Adélie Land as part of the Collaborative East Antarctic Marine Census (CEAMARC) project. The acoustic component of this survey was conducted using a scientific echosounder operating at 38 and 70 kHz to estimate the distribution and density of Antarctic krill (Euphausia superba) and ice krill (E. crystallorophias). In addition, the relationship between the vertical distribution of Antarctic krill and the water temperature structure along the 140°E meridian was investigated. Antarctic krill were distributed in the waters of the continental slope at 65-66°S and the maximum value of the mean areal density ρ in 1 nautical mile (nmi) intervals was 4344 inds. m-2. Ice krill were distributed in the neritic waters of the continental shelf to the south of the 66°S and the maximum ρ in 1 nmi intervals was 23,669 inds. m-2. Along the 140°E meridian, Antarctic krill were mainly distributed at the water temperatures below 0.5 °C. Although they were mostly distributed shallower than approximately 100 m, dense aggregations at approximately 180-200 m were also observed, which coincided with a depression of the water temperature structure. © 2011 Elsevier B.V. and NIPR.
  • Atsushi Ono, Masato Moteki, Kazuo Amakasu, Ryoji Toda, Naho Horimoto, Daisuke Hirano, Takashi Ishimaru, Graham W. Hosie
    Polar Science 5 2 146 - 165 2011年08月 [査読有り][通常論文]
     
    The distribution and community structure of euphausiids and the population structure of Euphausia superba were investigated mainly along 140°E off Adélie Land in the Indian Ocean sector of the Southern Ocean during the austral summers of 2003, 2005 and 2008. Euphausiids were collected from six discrete depth layers, primarily between 0 and 2000 m, using an RMT 8 net. Euphausia frigida and Euphausia triacantha mainly occurred north of the Southern Boundary of the Antarctic Circumpolar Current (SB) whereas E. superba was distributed south of the SB, and occurred abundantly in the continental slope area where Antarctic Winter Water was observed. E. frigida and E. triacantha occurred in the upper 200 m during the night whereas they were mainly found below 200 m during the daytime. Cluster analysis on stations suggested that the SB is an important biological boundary for euphausiid communities. The population structure of E. superba in 2003 was different from that of 2005 and 2008. While large mature individuals dominated in 2003, small immature krill (juveniles and subadult males) were more abundant in 2005 and 2008. Further sea-ice extension in the preceding winter in 2005 and 2008 likely provided favourable conditions for spawning and survival. A cluster analysis based on similarity of the maturity stages of E. superba revealed that mature males and gravid females (stage IIIC-E) were mainly distributed in the offshore area and mesopelagic zone, while juveniles and subadult males were found in the epipelagic zone of the continental slope area. Therefore, it is considered that E. superba migrates to the offshore area and mesopelagic zone as it grows. © 2011 Elsevier B.V. and NIPR.
  • Philippe Koubbi, Percy Alexander Hulley, Patrice Pruvost, Pauline Henri, Jean Philippe Labat, Victoria Wadley, Daisuke Hirano, Masato Moteki
    Polar Science 5 2 195 - 210 2011年08月 [査読有り][通常論文]
     
    The pelagic fish community of the Dumont d'Urville Sea (East Antarctica) was investigated during the 2008 austral-summer using IYGPT (International Young Gadoid Pelagic Trawl) samples taken in different depth layers from the surface to 1000 m. The aim of this paper is to describe the mesopelagic fish community and its size distribution. The family Myctophidae dominated the mesopelagic ichthyofauna, while bathylagids were abundant in deeper hauls. Bathylagids. , Cyclothone spp., Gymnoscopelus opisthopterus, Electrona antarctica, Protomyctophum bolini, and Krefftichthys anderssoni were the most abundant taxa in the samples and showed size stratification with depth. Community and size structuring appear to be influenced by the hydrology and by the proximity of the continental margin, as well as a relationship to the circulation of the Modified Circumpolar Deep Water. © 2011 Elsevier B.V. and NIPR.
  • Philippe Koubbi, Catherine Ozouf-Costaz, Anne Goarant, Masato Moteki, Percy Alexander Hulley, Romain Causse, Agnès Dettai, Guy Duhamel, Patrice Pruvost, Eric Tavernier, Alexandra L. Post, Robin J. Beaman, Stephen R. Rintoul, Toru Hirawake, Daisuke Hirano, Takashi Ishimaru, Martin Riddle, Graham Hosie
    Polar Science 4 2 115 - 133 2010年08月 [査読有り][通常論文]
     
    Ecoregions are defined in terms of community structure as a function of abiotic or even anthropogenic forcing. They are meso-scale structures defined as the potential habitat of a species or the predicted communities geographic extent. We assume that they can be more easily defined for long-lived species, such as benthos or neritic fish, in the marine environment. Uncertainties exist for the pelagic realm because of its higher variability, plus little is known about the meso- and bathypelagic zones. A changing environment and modification of habitats will probably drive new communities from plankton to fish or top predators. We need baseline studies, such as those of the Census of Antarctic Marine Life, and databases like SCAR-MarBIN as tools for integrating all of these observations. Our objective is to understand the biodiversity patterns in the Southern Ocean and how these might change through time. © 2010 Elsevier B.V.
  • Daisuke Hirano, Yujiro Kitade, Hideki Nagashima, Masaji Matsuyama
    Journal of Oceanography 66 1 95 - 104 2010年01月 [査読有り][通常論文]
     
    The strength of mixing due to turbulence in the Antarctic Slope Front (ASF) region was investigated using CTD (conductivity-temperature-depth profilers) observations and direct measurements of turbulence conducted off Adélie Land, East Antarctica along 140°E from the 12th-14th February, 2005. The strongest horizontal gradient of the ASF was located below 300 m depth near the 1000 m isobath. The turbulent measurements revealed that the energy dissipation rate frequently exceeded 10-8 Wkg-1 on the continental shelf and upper slope regions. Turbulent diffusivities near the shelf break were higher than 10-3 m2s-1. Near the ASF the average turbulent heat flux was 5.7 Wm-2 and 1.1 Wm-2 across the temperature minimum layer to 250 m and from 300 to 600 m, respectively. The distribution of the high dissipation rate was consistently explained by the characteristic curve of the M2 internal wave emanating from the shelf break and continental slope. The water mass observed in the ASF below 300 m in the continental slope comprised Modified Circumpolar Deep Water and low salinity Shelf Water originating from either the upper layer of the Adélie Depression or the Adélie Bank, and produced by boundary mixing near the shelf break. © Springer Science+Business Media B.V. 2010.

その他活動・業績

受賞

  • 2012年03月 日本海洋学会奨励論文賞
     
    受賞者: 平野大輔

共同研究・競争的資金等の研究課題

  • 東南極白瀬氷河域の顕著な底面融解を引き起こす背景要因
    日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2020年04月 -2023年03月 
    代表者 : 平野 大輔
  • 東南極トッテン棚氷域における氷床海洋相互作用の観測研究
    日本学術振興会:科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2020年04月 -2022年03月 
    代表者 : 平野 大輔
  • ポリニヤを起点とする熱塩/物質循環
    日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 2017年04月 -2020年03月 
    代表者 : 大島 慶一郎, 深町 康, 平野 大輔, 二橋 創平, 青木 茂, 西岡 純
     
    平成30年度は、北極海、南極海、オホーツク海の3海域でのポリニヤ内での係留系観測とその解析を中心に研究を行った。北極チャクチ海ポリニヤにおいて蓄積されたADCP(Acoustic Doppler Current Profiler)と濁度計のデータの解析からは、海中でのフラジルアイス生成と海底堆積物の巻き上がりが同時に起こり、それによって海氷内に鉄等の堆積物が取り込まれる過程(suspension freezing)が頻繁に起こることが強く示唆された。オホーツク海サハリンポリニヤでの解析では、強風かつ強い流れがあるときに、海底まで及ぶ全層でフラジルアイス生成が起こることが示された。これは非常に効率的な海氷生産過程をもたらし、このポリニヤ内での海氷生産の半分以上はフラジルアイス生成によるものであることがデータから示唆された。昨年度に南極ケープダンレーポリニヤ内に設置された係留系が第60次日本南極地域観測隊によって回収された。この系には周波数の異なる3台のADCPと濁度計・水温塩分計が付いており、海中でのフラジルアイス生成や海底堆積物の巻き上がりに対して、今までにない定量性の高い解析が可能となる。また、白鳳丸としらせにより、ケープダンレーポリニヤ内とその沖の底層水の通り道に、ADCPや時系列採水器が付いた計5つの係留系を設置した。さらに、最新の衛星マイクロ波放射計であるAMSR2からフラジルアイスを検知できるアルゴリズムを開発した。今後、衛星海氷データと係留系データの組み合わせによる解析から、ポリニヤでの高海氷生産システムや物質循環の理解が深まることが期待される。オホーツク海に関しては、過去に蓄積されたフロートデータの解析から、北西陸棚ポリニヤからの高密度陸棚水が千島海盆内で他の水塊と混合してオホーツク海中層水になる過程などを明らかにした。
  • 東南極沿岸域の氷床ー海氷ー海洋相互作用における暖水流入の影響評価
    日本学術振興会:科学研究費助成事業 若手研究(B)
    研究期間 : 2017年04月 -2020年03月 
    代表者 : 平野 大輔
     
    (1)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導かれた白瀬氷河―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。大陸斜面域での卓越風の季節変動が冬季水の厚みを変化させるプロセスを介し、白瀬氷河舌下への周極深層水の流入量および氷河舌の底面融解量をコントロールする主要因になり得ることを示した。この結果を、関連する国際学会やシンポジウムにて発表した。 (2)第59次南極地域観測隊(JARE)において白瀬氷河舌の上に設置したアイスレーダー(ApRES)のデータを回収し、1年以上にわたる貴重な氷河学データの取得に成功した。メンテナンス後に再設置し、さらに1台のApRES設置を行い、現在2台のApRESが順調に観測を継続中である。ApRESデータの予備的な解析を行い、従来の衛星観測や上記の海洋観測や数値モデル結果が示す白瀬氷河舌の高い底面融解率を支持する結果を得ている。 (3)JARE59次隊でトッテン氷河棚氷の前面海洋にて取得した海洋観測データを解析し、0℃を超える外洋起源の暖水(周極深層水)が深いトラフに沿ってトッテン棚氷の下へと流入していること、またその水温が過去観測された水温と比較して高いことが明らかになった。さらに、2018年12月から2019年3月に実施された水産庁「開洋丸」の南極調査航海に参加し、トッテン棚氷冲大陸斜面域の多地点にて空間的に詳細な海洋観測を実施し、良好な海洋物理パラメータのプロファイルと海水サンプルを取得した。これらのデータは、トッテン棚氷の底面を融解させる暖水の外洋から南極大陸縁辺への流入・循環プロセスを解明する上で、極めて重要なデータとなる。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2015年04月 -2019年03月 
    代表者 : 深町 康, 大島 慶一郎, 伊東 素代, プニュシコフ アンドレイ, 平野 大輔
     
    アラスカ北部沿岸域で実施した係留観測により、海氷厚の時系列データがそれ以前の観測と合わせて8年分蓄積された。そのデータの解析により、海氷厚に大きな経年変動が存在することを示し、その要因がこの海域の風による海氷の漂流パターンの変動にあることを明らかにした。
    係留観測によって得られた海洋の時系列データを用いて、この海域に存在する薄氷域の形成・維持は海氷の沖向きの風による輸送だけでなく、同じ沖向きの風によって湧昇した中層の高温水によっても成されており、この海域で冬季に生成される海水は太平洋起源だけでなく、大西洋起源の海水の影響も受けることを示した。
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2011年04月 -2015年03月 
    代表者 : 北出 裕二郎, 田村 岳史, 溝端 浩平, 嶋田 啓資, 青木 茂, 平野 大輔, 芦田 将成, 鈴木 萌, 白井 優, 笠島 克恵
     
    南極海表層水の低塩化に伴う南極底層水の変質と深層循環に及ぼす影響を評価するため、東京海洋大学研究練習海鷹丸により2012年から2015年の毎年1月に南極海110°E及び140°E周辺海域で、水温・塩分場の観測、長期係留観測、乱流観測等を実施した。本観測では、中規模ポリニヤを起源とした南極底層水の生成を世界で初めて明らかにし、オーストラリア南極海盆の底層水上部へと沈み込んでいることを示した。底層水の顕著な低塩化は、140°Eだけでなく110°Eでも認められ、特に、昇温も認められた2014年には海盆底層水の密度が相対的に軽くなり、ビンセネス湾起源底層水が海盆底層水下部まで達していることが分かった。


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