Relationship between glacial CO2 drawdown and mercury cycling in the western South Atlantic: An isotopic insight

Abstract

Abstract Pronounced changes in the deep Atlantic circulation occurred during glacial stages, which affected the global carbon distribution and the biogeochemical cycles of other elements. Previous studies demonstrated that oceanic mercury is sensitive to the same kind of processes that affect the carbon cycle in glacial–interglacial time scales. We used Hg isotopes to elucidate Hg cycling during the last two glacial–interglacial transitions in the subtropical western South Atlantic. Mass-dependent fractionation (MDF, δ202Hg) and mass-independent fractionation (MIF, Δ199Hg) show significant variations and shift toward higher and lower values during the penultimate and Last Glacial Maximum periods, respectively. δ202Hg variability is in-phase with periods of lower atmospheric CO2 and benthic δ13C, suggesting that MDF is affected by the same mechanisms that led to atmospheric CO2 drawdown during glacial stages. In contrast, terrestrial Hg input to our site, boosted by lower sea level and exposure of the continental shelf, dominates the Δ199Hg variability.