南極大陸周辺で発見された新たな海水経路(New Seawater Pathways Discovered around Antarctica)

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2024-06-18 カリフォルニア工科大学(Caltech)

南極大陸周辺で発見された新たな海水経路(New Seawater Pathways Discovered around Antarctica)
Measurements of temperature and salinity being collected from the R/V Nathaniel B. Palmer in the Bellingshausen Sea, Southern Ocean. The loss of volume of ice shelves in this region of West Antarctica has increased rapidly in recent decades.
Credit: Andrew Thompson

気候変動による温暖化で南極の氷棚が急速に融解しています。この融解は主に氷棚下の温水が原因ですが、融解水が海に流れ込むと海流に運ばれ、さらに下流の氷棚の融解速度に影響を与えます。カルテックのアンディ・トンプソン教授の研究チームは、10年以上にわたり南極海を研究し、新しい海流がベルリングスハウゼン海で発見されました。この海は大西洋と太平洋からの温水が最初に氷棚に到達する場所です。シールに取り付けたセンサーや自律型海中探査機からのデータを用いて、研究チームは二つの融解水の経路を特定しました。この研究は、個々の氷棚の融解が南極全体の海洋循環と氷棚融解にどのように影響するかを理解するための重要な一歩となります。

<関連情報>

ベリングスハウゼン海からアムンゼン海までの海盆間交流の経路 Pathways of Inter-Basin Exchange From the Bellingshausen Sea to the Amundsen Sea

M. Mar Flexas, Andrew F. Thompson, Megan L. Robertson, Kevin Speer, Peter M. F. Sheehan, Karen J. Heywood
Journal of Geophysical Research: Oceans  Published: 02 June 2024
DOI:https://doi.org/10.1029/2023JC020080

Abstract

The West Antarctic Ice Sheet is experiencing rapid thinning of its floating ice shelves, largely attributed to oceanic basal melt. Numerical models suggest that the Bellingshausen Sea has a key role in setting water properties in the Amundsen Sea and further downstream. Yet, observations confirming these pathways of volume and tracer exchange between coast and shelf break and their impact on inter-sea exchange remain sparse. Here we analyze the circulation and distribution of glacial meltwater at the boundary between the Bellingshausen Sea and the Amundsen Sea using a combination of glider observations from January 2020 and hydrographic data from instrumented seals. Meltwater distributions over previously unmapped western regions of the continental shelf and slope reveal two distinct meltwater cores with different optical backscatter properties. At Belgica Trough, a subsurface meltwater peak is linked with hydrographic properties from Venable Ice Shelf. West of Belgica Trough, the vertical structure of meltwater concentration changes, with peak values occurring at greater depths and denser isopycnals. Hydrographic analysis suggests that the western (deep) meltwater core is supplied from the eastern part of Abbot Ice Shelf, and is exported to the shelf break via a previously-overlooked bathymetric trough (here named Seal Trough). Hydrographic sections constructed from seal data reveal that the Antarctic Coastal Current extends west past Belgica Trough, delivering meltwater to the Amundsen Sea. Each of these circulation elements has distinct dynamical implications for the evolution of ice shelves and water masses both locally and downstream, in the Amundsen Sea and beyond.

Key Points

  • Hydrographic observations identify both shelf-break and coastal meltwater pathways from the western Bellingshausen Sea into the Amundsen Sea
  • Differences in optical backscatter properties associated with meltwater are related to distinct coast-to-shelf break pathways
  • The main pathway to the shelf break is via Seal Trough, identified as the de facto western boundary of the Bellingshausen Sea

Plain Language Summary

Floating ice shelves in West Antarctica are thinning, which is largely due to melting of the ice shelf base by the ocean. Here, measurements of ocean temperature, salinity, and dissolved oxygen, collected by a remotely-controlled underwater vehicle (a glider), are used to estimate the amount of ice shelf meltwater released in the Bellingshausen Sea. Distinct cores of meltwater can be distinguished by the amount of suspended material that is present in the water, which we attribute to meltwater following different circulation pathways after entering the ocean. Historical data from seals equipped with temperature and salinity sensors provide additional information about how the meltwater circulates in the region. The seal data show the presence of a narrow coastal current that brings meltwater from the Bellingshausen Sea into the Amundsen Sea. The pathways of meltwater revealed in this study suggest an important influence of the Bellingshausen Sea on ice shelves throughout West Antarctica.

1702地球物理及び地球化学
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