Meridional shifts of Brazil-Malvinas Confluence since the Last Glacial Maximum

Abstract

The Brazil-Malvinas Confluence (BMC) is a highly dynamic convergence of surface currents in the southwestern South Atlantic, where the warm Brazil Current (BC) from the tropical Atlantic meets the cold Malvinas Current (MC) that originates from the northern branch of the Antarctic Circumpolar Current. Meridional shifts of the BMC play an important role in controlling the heat transfer from the tropical Atlantic to the higher latitudes of the South Atlantic. In this study, the marine core GeoB13861–1 is analyzed for pollen, spores, freshwater algae, and organic-walled dinoflagellate cysts (dinocysts) to reconstruct marine and terrestrial paleoenvironmental changes in southeastern South America since the Last Glacial Maximum (LGM). The results indicate that during LGM, the BMC was at its northernmost location due to the strong influence of the MC. During that period, exposed coastal areas of Argentina were dominated by salt marshes shaped by low global sea level. From ∼18 to 15 cal kyr BP, the BMC migrated southward, contributing to more humid conditions on the adjacent continent. As sea level rose, former salt marshes along the coast were gradually flooded. The increased presence of Nothofagus and Podocarpus pollen in the marine record suggests a slight expansion of Andean forests during the Late Glacial, indicating the adjacent continental regions shifted to wetter conditions. Notably, our study confirms that the signals of abrupt climate events, such as Heinrich Stadial 1 (HS1) and Younger Dryas (YD), are well-preserved in the marine sediment records. Our new findings provide clear evidence of the bi-polar sea saw effect during HS1, marked by abrupt ocean warming in the South Atlantic.