Response of the subtropical North Atlantic surface hydrography on deglacial and Holocene AMOC changes

Abstract

The North Atlantic subtropical gyre (STG) circulates warm waters between 10 and 40°N and is a potential area of heat storage during periods of reduced North Atlantic Meridional Overturning Circulation (AMOC), when warm salt-rich waters are retained in the subtropics. In this study, we investigated multicentennial to millennial scale changes in subtropical North Atlantic hydrography in response to AMOC changes during the last deglaciation and early Holocene, using sediment cores MD08-3180 and GEOFAR KF16. The coring site (38°N) is situated near the boundary between transitional eastern North Atlantic waters and STG waters that is formed by the Azores Front. Hydrographic changes are reconstructed using new stable isotope data of benthic and subsurface dwelling planktonic foraminifera, Mg/Ca measurements on planktonic foraminifera, and planktonic foraminifera abundances that are supplemented with published sea surface temperature and stable isotope data. These multiproxy data indicate a close coupling between the latitudinal position of the northern STG boundary and deglacial AMOC modes. During weak AMOC phases (Heinrich event 1, Younger Dryas (YD), 8.2 ka event), Northern Hemisphere subpolar water reached down to the northern STG boundary, displacing the boundary southward. During the Bølling-Allerød warm period, a strong warming trend of the subtropical region to 19°C is observed. A cooling of the sea surface temperature by 6°C during the YD is accompanied by ongoing northward transport of warm subsurface water that might have contributed to the restart of AMOC. Key Points Azores Front position is coupled with AMOC strength over the last deglaciation Azores Front displaced southward by meltwater during the H1 and the 8.2 event Divers subsurface and surface warming pattern at Azores during weak AMOC.