THE INFLUENCE OF SOUTHERN OCEAN WINDS AND NORTHERN HEMISPHERE MELT WATER ON THE ATLANTIC MERIDIONAL OVERTURNING CIRCULATION

The Atlantic Meridional Overturning Circulation (AMOC) plays a critical role in the modulation of Earth’s climate on a variety of time scales. Observations and simulations with General Circulation Models (GCMs) demonstrate that the northward flow of the Gulf Stream, enhanced by North Atlantic Deep Water formation, warms Northern Europe due to the transfer of heat from the ocean to the atmosphere. Modulation of this heat flux is intimately coupled to the Atlantic Multidecadal Oscillation on geologically short timescales and glacial interglacial variations in NADW formation on Milankovitch timescales. While physical oceanographers have long argued for the importance of Southern Ocean winds in driving the AMOC, within the modeling and paleoceanographic community, considerable effort has focused on the role of meltwater influx as a principle modulator of NADW flux. Here we employ an analytical physical oceanographic model coupled with paleoceanographic proxies to evaluate the relative importance of both southern ocean winds and northern hemisphere meltwater fluxes. Paleoceanographic analysis supports results of the Sandal-Nof analytical model suggesting that the AMOC is controlled by the interplay of the Subantarctic Westerlies, North Hemisphere freshwater flux and the opening and closing of Bering Strait. The shallow Bering Strait plays an important role in modulating the interplay of the Subantarctic Westerlies and freshwater fluxes because it controls the inter-hemispheric connection of the Pacific, Arctic and Atlantic basins. When the Bering Strait opens, it creates a gigantic “island” allowing continuity of sea level around the Americas. Increasing the Subantarctic Westerlies then warms the North Atlantic Deep Water (NADW) by enhancing the near surface, cross-equatorial flow from the Southern Ocean to the Northern Hemisphere. This cross-equatorial flow increases the AMOC and decreases the Arctic out flow into the Atlantic. Decreasing the Northern Hemisphere freshwater flux stimulates NADW formation by increasing North Atlantic surface salinity and increases the flow through the Bering Strait to replace the sinking NADW flux. As the Subantarctic Westerlies increase, a greater freshwater flux is required to weaken the AMOC.