[A-CG42] 北極域の科学

[ACG42-10] Multidecadal changes in sea ice melt at the gates of the Western Arctic Ocean: Bering Sea and Baffin Bay

*Vigan Mensah¹、Kay I. Ohshima^1,2 (1.Institute of Low Temperature Science, Hokkaido University、2.Arctic Research Center, Hokkaido University)

キーワード：Arctic, Sea Ice, Glacier, Freshwater budget, Climate change

The Western Arctic Ocean (Chukchi Sea, Beaufort Sea) is an essential region of the Arctic Ocean, as it is a reservoir of freshwater for the ocean, and is strongly influenced by the cycle of sea ice. This region is connected to the Pacific Ocean via the Bering Sea, which represents the gateway for freshwaters from the Pacific Ocean to the western Arctic. On the other end of this region, are the Fram Strait and the Baffin Bay/Labrador Sea, through which freshwater from the western Arctic outflows to the Atlantic Ocean. Both these entrance and exit gates to the western Arctic are also sources of freshwater via sea ice or glacier melt, precipitations and river runoff. In the context of a warming climate and Arctic amplification, it is crucial to document the changes in the freshwater budget during summer, when most freshwater inputs occur. In this presentation, we will briefly introduce the results of two recently submitted manuscripts on the multidecadal changes in the freshwater sources of the Bering Sea and the Baffin Bay/Labrador Sea, with a special focus on sea ice melt. In both studies, the freshwater or/and meltwater thickness were estimated from ocean data of temperature and salinity, by detecting the near-surface salinity deficit typical of spring and summer freshwater inputs by sea ice and other freshwater sources. This allows us to produce climatologies and time series of freshwater or/and meltwater thickness from 1950 to 2020, longer than any other observation-based sea ice records. In the Bering Sea, our results suggest that the sea ice meltwater amount has declined suddenly by about 10% in the early 1980s, which has affected the water column properties and stratification over the shallow Bering shelf. In the Baffin Bay and Labrador Sea, a steady decline in sea ice melt, representing 30% as of today, has been occurring from the mid-1990s. This decline in freshwater supply by sea ice is however surpassed by an increase in the melting of the glaciers around Baffin Bay, and by remote sources of freshwater possibly originating from the Beaufort Sea, Hudson Bay or East Greenland.