Paleoceanographic evolution of the Western South Atlantic Ocean circulation: a hotspot of evidence for global climate changes

Abstract

The South Atlantic western boundary current system is strategically embedded in the general framework of the large-scale ocean circulation. The anticyclonic South Atlantic subtropical gyre (SASG) provides the means by which the upper-limb of the Atlantic Meridional Overturning Circulation (AMOC) is advected northward, up to the point where the flow at its Northern boundary (represented by the Southern South Equatorial Current, sSEC) meets the South American coast and is forced to bifurcate either southward - recirculating in the SASG - or northward, continuing the AMOC upper-limb path. The resulting three-dimensional flow pattern is characterized by a multi-layer system of inversed-flowing currents, where the sSEC bifurcation sets the interplay between both dominant circulation features. This project is intended to reconstruct the sSEC bifurcation index for time-scales ranging since the Last Glacial Maximum, using it as a fingerprint for low-frequency variations in the AMOC and the general ocean circulation. By monitoring the spatio-temporal evolution of the bifurcation and the generated western boundary currents along depth, it is possible to make associations with the large-scale circulation and infer periods of stronger/weaker meridional overturning associated with AMOC modes as well as periods of spinned-up/slower gyre circulation. (AU)