Control of Bering Strait transport by the meridional overturning circulation

Theoretical understanding of the processes controlling the climatologically averaged flow through Bering Strait is lacking. It is well-established that Bering Strait mean transport is balanced by a sea-level difference between the North Pacific and the Arctic ocean, but no mechanism has been proposed to explain this sea-level difference. Previous work has shown that the depth of the mid-depth isopycnals is larger in the Indo-Pacific than in the Atlantic due to interbasin exchange occurring around South Africa. This difference in isopycnal depths, which amounts to denser water in the Atlantic than in the Pacific, causes the sea-level height in the Indo-Pacific to be higher than in the Atlantic, as observed. In the highest latitudes of the Northern Hemisphere, this isopycnal-depth difference is amplified by outcropping of several isopycnals in the North Atlantic and in the Arctic, but not in the Pacific. Because the depths of these outcropping isopycnals is associated with the dynamics of the upper branch of the Atlantic meridional overturning circulation (AMOC), we conjecture that the sea-level difference between the North Pacific and the Arctic/North Atlantic is primarily controlled by the wind-stress in the Antarctic Circumpolar region, since this forcing powers the AMOC. This implies that if the sinking associated with the meridional overturning were to occur in the North Pacific rather than the North Atlantic, then the Bering Strait flow would reverse. This conjecture is encapsulated in a simple box model and it is confirmed by a series of numerical experiment in a simplified geometry of the world ocean, forced by steady surface wind-stress, temperature and freshwater fluxes.