Articles | Volume 13, issue 3
Research article
09 Mar 2017
Research article |  | 09 Mar 2017

Changes in Holocene meridional circulation and poleward Atlantic flow: the Bay of Biscay as a nodal point

Yannick Mary, Frédérique Eynaud, Christophe Colin, Linda Rossignol, Sandra Brocheray, Meryem Mojtahid, Jennifer Garcia, Marion Peral, Hélène Howa, Sébastien Zaragosi, and Michel Cremer

Abstract. This paper documents the evolution over the last 10 kyr of one of the key parameters of climate: sea-surface temperatures (SSTs) in the North Atlantic. We focus on the southern Bay of Biscay, a highly sensitive oceanographic area regarding the dynamics of the North Atlantic subpolar and subtropical gyres (SPG and STG respectively). This site furthermore offers unique sedimentary environments characterized by exceptional accumulation rates, enabling the study of Holocene archives at (infra)centennial scales. Our results mainly derive from planktonic foraminiferal association analysis on two cores from the southern Landes Plateau. These associations are used as the basis of modern analogue technique transfer functions to track past hydrographical changes. SST reconstructions were thus obtained at an exceptional resolution and compared to a compilation of Holocene records from the northeastern North Atlantic. From this regional perspective are shown fundamental timing differences between the gyre dynamics, nuancing classical views of a simple meridional overturning cell. Our study highlights that western Europe underwent significant oscillations of (annual) SST during the last 10 kyr. During well-known intervals of mild boreal climate, warm shifts of more than 3 °C per century are accurately concomitant with positive sea-surface temperature anomalies and rise of micropalaeontological indicators of gyre dynamics in the northern North Atlantic, pointing to periods of greater intensity of the North Atlantic Current (SPG cell especially). Conversely, the SST signal records short-term cold anomalies which could be related to weaker SPG dynamics.

Short summary
In the boreal Atlantic, the subpolar and subtropical gyres (SPG and STG respectively) are key elements of the Atlantic Meridional Overturning Circulation (AMOC) cell and contribute to climate modulations over Europe. Here we document the last 10 kyr evolution of sea-surface temperatures over the North Atlantic with a focus on new data obtained from an exceptional sedimentary archive retrieved the southern Bay of Biscay, enabling the study of Holocene archives at (infra)centennial scales.