Last Glacial - Holocene variability of the European Slope Current, NE Atlantic

The upper branch of the Atlantic Meridional Overturning Circulation (AMOC) in the mid-latitudes of the Northeast Atlantic remains poorly studied. This study provides a complete overview of the glacial, deglacial and Holocene dynamics of the easternmost portion of the AMOC upper branch, namely the European Slope Current (ESC) and its glacial equivalent known as the Glacial Eastern Boundary Current (GEBC). This is achieved through the study of the sediment core SU81-44 retrieved from the southern Bay of Biscay (BoB) (similar to 1000 m water depth), and by using a multiproxy approach (i.e. benthic foraminiferal assemblage, grain size proxies, oxygen and carbon stable isotopes, and neodymium isotopic composition of foraminiferal shells). During the glacial period and the onset of the deglaciation, the grain size proxies at SU81-44 fluctuate significantly. These fluctuations are coherent with changes in relative densities of benthic foraminiferal indicator species of current strength and ventilation, thus highlighting significant changes in the GEBC vigor through time. The SU81-44 data confirm the Dansgaard-Oeschger interstadial/faster-stadial/slower flow pattern previously observed in northern BoB. Our results also provide new constraints on the strength of the slope current during the late deglaciation and Ho-locene period with a significant reinvigoration of the ESC, and by extension the upper branch of the AMOC during the Bolling-Allerod warming. This seems to confirm the crucial role of the ESC in deep water formation at high northern latitudes, as it is the case today. Finally, our data show a progressive weakening of the ESC during the Holocene. We hypothesize a link with a long-term decrease in the density gradient between low and high latitudes that can be attributed to long term changes in insolation and the strength of the subpolar gyre dynamics.

Automated summary

This study provides a comprehensive overview of the dynamics of the upper branch of the Atlantic Meridional Overturning Circulation (AMOC) in the mid-latitudes of the Northeast Atlantic. It focuses on the European Slope Current (ESC) and its glacial equivalent known as the Glacial Eastern Boundary Current (GEBC). The study reveals significant changes in flow strength and ventilation during the glacial and deglaciation periods, as well as a gradual weakening of the slope current during the Holocene.