Mercury deposition in the western tropical South Atlantic during the last 70 ka

Abstract

Mercury is released via natural and anthropogenic sources. Atmospheric deposition via dry and wet deposition is the main source of mercury to the continents and oceans. In the oceans, organic matter is the primary driver of mercury accumulation in marine sediments. Previous studies reported that mercury is sensitive to past climate changes and that global and regional climatic factors can control its environmental dynamics. Here, we used sediment core M125–95-3 collected at the western tropical South Atlantic to investigate mercury deposition and accumulation changes in the marine realm over the last 70 ka. Our records show higher concentration during the glacial period than in the interglacial period due to increased atmospheric dust. On millennial-scale events, the increased residence time of North Atlantic Deep Water enhanced the regenerative scavenging of mercury, which reduced mercury concentration in M125–95-3 core. In addition, the dilution effect might have reduced the mercury concentration further during Heinrich stadials due to increased terrigenous input via the São Francisco River. Altogether, the results suggest a strong influence of deep ocean circulation on the deposition and accumulation of mercury in marine sediments in the western tropical South Atlantic on millennial timescales, highlighting long-term oceanic processes that act on the geochemical cycle of mercury.