基本情報

所属

• 低温科学研究所　水・物質循環部門

職名

• 助教

連絡先

• Yoshihiro.Nakayamalowtem.hokudai.ac.jp

科研費研究者番号

• 30840201

J-Global ID

• 201901007614414758

プロフィール

• 　南極域の海洋は、大きく変化し始めている兆しを見せ、気候変動、海面上昇を通じて、我々の生活に大きな影響を及ぼす可能性があります。その理解のために、現場観測データ、人工衛星、数値モデルを統合的に利用しながら、今南極の海で起きている変化を捉え、将来を予測するための研究を行なっています。特に、南極氷床、棚氷、南大洋の研究をしていて、南極による海面上昇への寄与やそれを引き起こす海の役割に注目しています。研究は、日本だけでなく、アメリカ、ヨーロッパの研究所と共同で実施しています。興味のある学生の方は、気軽にメールでお問い合わせください。研究室への訪問も歓迎いたします。以下に、計算機を用いたシミュレーションの一例を示すのでご覧ください。

  
  

   

  
  

研究キーワード

• 極域海洋学、棚氷海洋相互作用、海面上昇、地球温暖化、気候変動   

研究分野

• 自然科学一般 / 大気水圏科学 / 極域海洋学

担当教育組織

•  修士課程　環境科学院
•  博士課程　環境科学院

職歴

• 2018年11月 - 現在 北海道大学 低温科学研究所 助教
• 2016年03月 - 2018年10月 NASA Jet Propulsion Laboratory NASA Postdoctoral Fellow
• 2015年10月 - 2016年02月 University of California Irvine Postdoctoral Scholar
• 2015年07月 - 2015年09月 NASA Jet Propulsion Laboratory Research Visitor
• 2014年12月 - 2015年02月 Alfred Wegener Institute Postdoctoral Scholar

学歴

• 2011年06月 - 2015年02月   University of Bremen   Alfred Wegener Institute
• 2009年04月 - 2011年03月   北海道大学   大学院地球環境科学研究院
• 2005年04月 - 2009年03月   名古屋大学   工学部   機械 航空工学科

研究活動情報

論文

• Helicopter‐Based Ocean Observations Capture Broad Ocean Heat Intrusions Toward the Totten Ice Shelf

  Yoshihiro Nakayama, Pat Wongpan, Jamin S. Greenbaum, Kaihe Yamazaki, Tomohide Noguchi, Daisuke Simizu, Haruhiko Kashiwase, Donald D. Blankenship, Takeshi Tamura, Shigeru Aoki

  Geophysical Research Letters 50 17 2023年09月11日 

  Abstract The recent discovery of warm ocean water near the Totten Ice Shelf (TIS) has increased attention to the Sabrina Coast in East Antarctica. We report the result of 6‐day helicopter‐based observations conducted during the 61st Japanese Antarctic Research Expedition (JARE61), revealing warm ocean water (0.5–1°C) occupying a large previously unsampled area of the Sabrina Coast (116.5°E−120°E) below 550–600 m. Along the TIS front, we observe modified Circumpolar Deep Water (mCDW) well above freezing (∼−0.7°C), consistent with previous work. We identify glacial meltwater outflow from the TIS cavity west of 116°E. No signs of mCDW intrusions toward the Moscow University Ice Shelf cavity are observed; however, those observations were limited to only two shallow (∼330 m) profiles. We also highlight the advantages of helicopter‐based observations for accessibility, speed, maneuverability, and cost‐efficiency. The combination of ship‐ and helicopter‐based observations using the JARE61 approach will increase the potential of future polar oceanographic observations.
• 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 

  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.
• Impact of Subglacial Freshwater Discharge on Pine Island Ice Shelf

  Yoshihiro Nakayama, Cilan Cai, Helene Seroussi

  Geophysical Research Letters 48 18 2021年09月20日
• Widespread Grounding Line Retreat of Totten Glacier, East Antarctica, Over the 21st Century

  Tyler Pelle, Mathieu Morlighem, Yoshihiro Nakayama, Hélène Seroussi

  Geophysical Research Letters 48 17 2021年09月08日
• Antarctic Slope Current Modulates Ocean Heat Intrusions Towards Totten Glacier

  Yoshihiro Nakayama, Chad A. Greene, Fernando S. Paolo, Vigan Mensah, Hong Zhang, Haruhiko Kashiwase, Daisuke Simizu, Jamin S. Greenbaum, Donald D. Blankenship, Ayako Abe‐Ouchi, Shigeru Aoki

  Geophysical Research Letters 48 17 2021年09月08日 

  The Totten ice shelf (TIS) in East Antarctica has received increasing attention in recent years due to high basal melt rates, which have been linked to a presence of warm modified Circumpolar Deep Water (mCDW) observed at the ice front. We show that mCDW on-shelf intrusions towards the TIS strengthen when the Antarctic Slope Current (ASC) weakens. This demonstrates that the ASC has a blocking effect and ASC weakening leads to on-shelf intrusions, as proposed by previous observational studies. The interannual variability of the ASC is controlled primarily by atmospheric and oceanic conditions beyond our regional model domain. We further show that heat intrusions onto the continental shelf off the TIS are not influenced by off-shelf warming but are enhanced with coastal freshening, suggesting positive feedback whereby ice melt and freshening upstream could start a chain reaction, leading to increased melt, and further coastal freshening.
• Dense water downslope flow and AABW production in a numerical model: Sensitivity to horizontal and vertical resolution in the region off Cape Darnley polynya

  Vigan Mensah, Yoshihiro Nakayama, Masakazu Fujii, Yoshifumi Nogi, Kay I. Ohshima

  Ocean Modelling 165 101843 - 101843 2021年09月 

  The formation of Dense Shelf Water (DSW) and Antarctic Bottom Water (AABW) in the Southern Ocean is an essential part of the thermohaline circulation, and understanding this phenomenon is crucial for studying the global climate. AABW is formed as DSW flows down the continental slope and mixes with the surrounding waters. However, DSW formation and its descent remains a poorly resolved issue in many ocean models. We, therefore, simulated the formation and descent of DSW and investigated the model sensitivities to horizontal and vertical grid spacings. The Massachusetts Institute of Technology general circulation model (MITgcm) was used for the region off Cape Darnley in East Antarctica, one of the main AABW production areas, where historical and mooring data are available for comparison. Simulations with coarse horizontal grid resolutions of order (10 km) yielded high volumes of DSW on the shelf. However, the largest part of this DSW was transformed into intermediate water and advected westward. Horizontal model resolutions equal to or higher than 2 km were required to simulate the descent of DSW and a realistic AABW production. Simulated time series at a mooring located at a depth of 2,600 m showed periodic fluctuations in velocity and temperature of 0.3 m.s(-1) and 0.5 degrees C, respectively, consistent with observations. We also found that high-resolution bathymetry datasets are crucial because the newly formed AABW volume was reduced by 20% when a smoother bathymetry was used on a 2-km resolution grid. Vertical resolution had little influence on model performance because the plume was much thicker (> 170 m) than the grids width. Therefore, reproducing the downslope flow of DSW and AABW formation in the Cape Darnley region can be achieved with a high horizontal resolution (<= 2 km) and a relatively coarse vertical resolution (similar to 100 m on the continental slope).
• Development of adjoint-based ocean state estimation for the Amundsen and Bellingshausen seas and ice shelf cavities using MITgcm–ECCO (66j)

  Yoshihiro Nakayama, Dimitris Menemenlis, Ou Wang, Hong Zhang, Ian Fenty, An T. Nguyen

  Geoscientific Model Development 14 8 4909 - 4924 2021年08月06日 

  Abstract. The Antarctic coastal ocean impacts sea level rise, deep-ocean circulation, marine ecosystems, and the global carbon cycle. To better describe and understand these processes and their variability, it is necessary to combine the sparse available observations with the best-possible numerical descriptions of ocean circulation. In particular, high ice shelf melting rates in the Amundsen Sea have attracted many observational campaigns, and we now have some limited oceanographic data that capture seasonal and interannual variability during the past decade. One method to combine observations with numerical models that can maximize the information extracted from the sparse observations is the adjoint method, a.k.a. 4D-Var (4-dimensional variational assimilation), as developed and implemented for global ocean state estimation by the Estimating the Circulation and Climate of the Ocean (ECCO) project. Here, for the first time, we apply the adjoint-model estimation method to a regional configuration of the Amundsen and Bellingshausen seas, Antarctica, including explicit representation of sub-ice-shelf cavities. We utilize observations available during 2010–2014, including ship-based and seal-tagged CTD measurements, moorings, and satellite sea-ice concentration estimates. After 20 iterations of the adjoint-method minimization algorithm, the cost function, here defined as a sum of the weighted model–data difference, is reduced by 65 % relative to the baseline simulation by adjusting initial conditions, atmospheric forcing, and vertical diffusivity. The sea-ice and ocean components of the cost function are reduced by 59 % and 70 %, respectively. Major improvements include better representations of (1) Winter Water (WW) characteristics and (2) intrusions of modified Circumpolar Deep Water (mCDW) towards the Pine Island Glacier. Sensitivity experiments show that ∼40 % and ∼10 % of improvements in sea ice and ocean state, respectively, can be attributed to the adjustment of air temperature and wind. This study is a preliminary demonstration of adjoint-method optimization with explicit representation of ice shelf cavity circulation. Despite the 65 % cost reduction, substantial model–data discrepancies remain, in particular with annual and interannual variability observed by moorings in front of the Pine Island Ice Shelf. We list a series of possible causes for these residuals, including limitations of the model, the optimization methodology, and observational sampling. In particular, we hypothesize that residuals could be further reduced if the model could more accurately represent sea-ice concentration and coastal polynyas.
• Multidecadal poleward shift of the southern boundary of the Antarctic Circumpolar Current off East Antarctica

  Kaihe Yamazaki, Shigeru Aoki, Katsuro Katsumata, Daisuke Hirano, Yoshihiro Nakayama

  SCIENCE ADVANCES 7 24 2021年06月 

  The southern boundary (SB) of the Antarctic Circumpolar Current, the southernmost extent of the upper overturning circulation, regulates the Antarctic thermal conditions. The SB's behavior remains unconstrained because it does not have a clear surface signature. Revisited hydrographic data from off East Antarctica indicate full-depth warming from 1996 to 2019, concurrent with an extensive poleward shift of the SB subsurface isotherms (>50 km), which is most prominent at 120 degrees E off the Sabrina Coast. The SB shift is attributable to enhanced upper overturning circulation and a depth-independent frontal shift, generally accounting for 30 and 70%, respectively. Thirty years of oceanographic data corroborate the overall and localized poleward shifts that are likely controlled by continental slope topography. Numerical experiments successfully reproduce this locality and demonstrate its sensitivity to mesoscale processes and wind forcing. The poleward SB shift under intensified westerlies potentially induces multidecadal warming of Antarctic shelf water.
• 南極域における観測データの再現性の高い数値モデルの開発と海洋棚氷相互作用の研究 : 2020年度日本海洋学会岡田賞受賞記念論文

  Yoshihiro Nakayama

  海の研究 29 6 233 - 244 2020年11月 [査読有り]
  
• Impact of West Antarctic ice shelf melting on Southern Ocean hydrography

  Yoshihiro Nakayama, Ralph Timmermann, Hartmut H. Hellmer

  The Cryosphere 14 7 2205 - 2216 2020年07月13日 [査読有り]
   

  Abstract. Previous studies show accelerations of West Antarctic glaciers, implying that basal melt rates of these glaciers were previously small and increased in the middle of the 20th century. This enhanced melting is a likely source of the observed Ross Sea (RS) freshening, but its long-term impact on the Southern Ocean hydrography has not been well investigated. Here, we conduct coupled sea ice–ice shelf–ocean simulations with different levels of ice shelf melting from West Antarctic glaciers. Freshening of RS shelf and bottom water is simulated with enhanced West Antarctic ice shelf melting, while no significant changes in shelf water properties are simulated when West Antarctic ice shelf melting is small. We further show that the freshening caused by glacial meltwater from ice shelves in the Amundsen and Bellingshausen seas can propagate further downstream along the East Antarctic coast into the Weddell Sea. The freshening signal propagates onto the RS continental shelf within a year of model simulation, while it takes roughly 5–10 and 10–15 years to propagate into the region off Cape Darnley and into the Weddell Sea, respectively. This advection of freshening modulates the shelf water properties and possibly impacts the production of Antarctic Bottom Water if the enhanced melting of West Antarctic ice shelves continues for a longer period.
• Pathways of ocean heat towards Pine Island and Thwaites grounding lines

  Yoshihiro Nakayama, Georgy Manucharyan, Hong Zhang, Pierre Dutrieux, Hector S. Torres, Patrice Klein, Helene Seroussi, Michael Schodlok, Eric Rignot, Dimitris Menemenlis

  SCIENTIFIC REPORTS 9 2019年11月 [査読有り][通常論文]
   

  In the Amundsen Sea, modified Circumpolar Deep Water (mCDW) intrudes into ice shelf cavities, causing high ice shelf melting near the ice sheet grounding lines, accelerating ice flow, and controlling the pace of future Antarctic contributions to global sea level. The pathways of mCDW towards grounding lines are crucial as they directly control the heat reaching the ice. A realistic representation of mCDW circulation, however, remains challenging due to the sparsity of in-situ observations and the difficulty of ocean models to reproduce the available observations. In this study, we use an unprecedentedly high-resolution (200 m horizontal and 10 m vertical grid spacing) ocean model that resolves shelf-sea and sub-ice-shelf environments in qualitative agreement with existing observations during austral summer conditions. We demonstrate that the waters reaching the Pine Island and Thwaites grounding lines follow specific, topographically-constrained routes, all passing through a relatively small area located around 104 degrees W and 74.3 degrees S. The temporal and spatial variabilities of ice shelf melt rates are dominantly controlled by the sub-ice shelf ocean current. Our findings highlight the importance of accurate and high-resolution ocean bathymetry and subglacial topography for determining mCDW pathways and ice shelf melt rates.
• Origin of Circumpolar Deep Water intruding onto the Amundsen and Bellingshausen Sea continental shelves

  Yoshihiro Nakayama, Dimitris Menemenlis, Hong Zhang, Michael Schodlok, Eric Rignot

  NATURE COMMUNICATIONS 9 2018年08月 [査読有り][通常論文]
   

  Melting of West Antarctic ice shelves is enhanced by Circumpolar Deep Water (CDW) intruding onto the Amundsen and Bellingshausen Seas (ABS) continental shelves. Despite existing studies of cross-shelf and on-shelf CDW transports, CDW pathways onto the ABS originating from further offshore have never been investigated. Here, we investigate CDW pathways onto the ABS using a regional ocean model. Simulated CDW tracers from a zonal section across 67 degrees S (SO4P) circulate along the Antarctic Circumpolar Current (ACC) and Ross Gyre (RG) and travel into ABS continental shelf after 3-5 years, but source locations are shifted westward by similar to 900 km along S04P in 2001-2006 compared to 2009-2014. We find that simulated on- and off-shelf CDW is similar to 0.1-0.2 degrees C warmer in the 2009-2014 case than in the 2001-2006 case together with changes in simulated ocean circulation. These differences are primarily caused by lateral, rather than surface, boundary conditions, implying that large-scale atmospheric and ocean circulations are able to control CDW pathways and thus off- and on-shelf CDW properties.
• Developments in Simulating and Parameterizing Interactions Between the Southern Ocean and the Antarctic Ice Sheet

  Xylar S. Asay-Davis, Nicolas C. Jourdain, Yoshihiro Nakayama

  CURRENT CLIMATE CHANGE REPORTS 3 4 316 - 329 2017年12月 [査読有り][通常論文]
   

  Recent advances in both ocean modeling and melt parameterization in ice-sheet models point the way toward coupled ice sheet-ocean modeling, which is needed to quantify Antarctic mass loss and the resulting sea-level rise. The latest Antarctic ocean modeling shows that complex interactions between the atmosphere, sea ice, icebergs, bathymetric features, and ocean circulation on many scales determine which water masses reach ice-shelf cavities and how much heat is available to melt ice. Meanwhile, parameterizations of basal melting in standalone ice-sheet models have evolved from simplified, depth-dependent functions to more sophisticated models, accounting for ice-shelf basal topography, and the evolution of the sub-ice-shelf buoyant flow. The focus of recent work has been on better understanding processes or adding new model capabilities, but a broader community effort is needed in validating models against observations and producing melt-rate projections. Given time, community efforts in coupled ice sheet-ocean modeling, already underway, will tackle the considerable challenges involved in building, initializing, constraining, and performing projections with coupled models, leading to reduced uncertainties in Antarctica's contribution to future sea-level rise.
• Observations and modeling of ocean-induced melt beneath Petermann Glacier Ice Shelf in northwestern Greenland

  Cilan Cai, Eric Rignot, Dimitris Menemenlis, Yoshihiro Nakayama

  GEOPHYSICAL RESEARCH LETTERS 44 16 8396 - 8403 2017年08月 [査読有り][通常論文]
   

  We update observationally based estimates of subaqueous melt, Q(m), beneath Petermann Glacier Ice Shelf (PGIS), Greenland, and model its sensitivity to oceanic thermal forcing, TF, and subglacial runoff, Q(sg), using the Massachusetts Institute of Technology general circulation model (MITgcm), in a two-dimensional domain, with 20m vertical and 40m horizontal resolution at the grounding line. We adjust the drag coefficient to match the observationally based Q(m). With the inclusion of Q(sg), the maximum melt rate (Q(m)(max)) is 2 times larger in summer and 1/3 larger annually than in winter. Q(m)(max) increases above linear with TF and below linear with Q(sg). We estimate that Q(m)(max) increased by 24% (+8.1m/yr) beneath PGIS from the 1990s to the 2000s from a 0.21 degrees C warming in ocean temperature and a doubling in Q(sg), hence contributing to its thinning. If the PGIS is removed, we estimate that the modeled melt rate near the grounding line will increase 13-16 times.
• Continued retreat of Thwaites Glacier, West Antarctica, controlled by bed topography and ocean circulation.

  H. Seroussi, Y. Nakayama, E. Larour, D. Menemenlis, M. Morlighem, E. Rignot, A. Khazendar

  Geophysical Research Letters 2017年04月 [査読有り][通常論文]
  
• Amundsen and Bellingshausen Seas simulation with optimized ocean, sea ice, and thermodynamic ice shelf model parameters,

  Y. Nakayama, D. Menemenlis, M. Schodlok E, Rignot

  Journal of Geophysical Research: Ocean 2017年04月 [査読有り][通常論文]
  
• On the difficulty of modeling Circumpolar Deep Water intrusions onto the Amundsen Sea continental shelf

  Yoshihiro Nakayama,, Ralph Timmermann, Michael Schorder, Hartmut Hellmer

  Ocean Modeling 2014年12月 [査読有り][通常論文]
  
• Modeling the spreading of glacial melt water from the Amundsen and Bellingshausen Seas.

  Y. Nakayama R. Timmermann C. B. Rodehacke M. Schröder H. H. Hellmer

  Geophysical Research Letters 2014年11月 [査読有り][通常論文]
  
• A Numerical Investigation of Formation and Variability of Antarctic Bottom Water off Cape Darnley, East Antarctica

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

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

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

  Y. Nakayama, M. Schroeder, H. H. Hellmer

  DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS 77 50 - 62 2013年07月 [査読有り][通常論文]
   

  The melting of Pine Island Ice Shelf (PIIS) has increased since the 1990 s, which may have a large impact on ice sheet dynamics, sea-level rise, and changes in water mass properties of surrounding oceans. The reason for the PIIS melting is the relatively warm (similar to 1.2 degrees C) Circumpolar Deep Water (CDW) that penetrates into the PIIS cavity through two submarine glacial troughs located on the Amundsen Sea continental shelf. In this study, we mainly analyze the hydrographic data obtained during ANTXXVI/3 in 2010 with the focus on pathways of the intruding CDW, PIIS melt rates, and the fate of glacial meltwater. We analyze the data by dividing CTD profiles into 6 groups according to intruding CDW properties and meltwater content. From this analysis, it is seen that CDW warmer than 1.23 degrees C (colder than 1.23 degrees C) intrudes via the eastern (central) trough. The temperature is controlled by the thickness of the intruding CDW layer. The eastern trough supports a denser CDW layer than the water mass in Pine Island Trough (PIT). The eastern intrusion is modified on the way into PIT through mixing with the lighter and colder CDW from the central trough. Using ocean transport and tracer transport calculations from the ice shelf front CTD section, the estimated melt rate in 2010 is similar to 30 m yr(-1), which is comparable to published values. From spatial distributions of meltwater content, meltwater flows along the bathymetry towards the west. When compared with earlier (2000) observations, a warmer and thicker CDW layer is observed in Pine Island Trough for the period 2007-2010, indicating a recent thickening of the CDW intrusion. (C) 2013 Elsevier Ltd. All rights reserved.
• Enhancement of Sea Ice Drift due to the Dynamical Interaction between Sea Ice and a Coastal Ocean

  Yoshihiro Nakayama, Kay I. Ohshima, Yasushi Fukamachi

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

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

受賞

• 2020年04月 日本海洋学会 岡田賞
   南大洋における海洋と棚氷の相互作用に関する研究
• 2016年03月 NASA NASAポスドクフェローシップ
  

教育活動情報

主要な担当授業