Southern component water-driven carbonate dissolution and carbon storage during the Last Glacial Maximum in the western South Atlantic

Abstract

Late Quaternary glacial-interglacial climate variability is related to the carbon cycle, with its feedback mechanisms amplifying the effects of orbital forcing. These processes account for a ∼80–100 ppm change in atmospheric CO₂, and are influenced, in part, by shifts in carbonate production, dissolution, and burial. The southern Brazilian continental margin is close to potential iron fertilisation sources, but the interplay of the region's productivity, water mass geometry, and carbonate dissolution remain underexplored. In this study we investigate core SIS-203 (1894 mbsl depth), covering the 31–7 ka interval. Planktonic foraminifera proxies indicate low productivity during the Last Glacial Maximum (LGM), with a slight increase during the deglaciation and into the Holocene. Authigenic foraminiferal εNd shows full influence of corrosive Southern Component Water (SCW) during the LGM, and decreased carbonate preservation supports this interpretation. Thus, despite the low biologically mediated dissolution at this site, carbonate preservation decreases during the LGM, similarly observed in other Atlantic basins. We propose that it is through water mass geometry changes (higher influence of SCW) that calcium carbonate preservation is affected. Changes in deep water mass stratification and circulation strengthened deep-ocean carbon sequestration during the LGM in the western South Atlantic, which may be linked to Southern Hemisphere climate dynamics.