Glacial-interglacial contrasts in the marine inorganic carbon chemistry of the Benguela Upwelling System

Abstract

Abstract. Upwelling regions are dynamic systems where relatively cold, nutrient- and CO₂-rich waters reach to the surface from the deep. CO₂ sink or source properties of these regions are dependent not only on the dissolved inorganic carbon content of the upwelled waters, but also on the efficiency of the biological carbon pump that provides constraint on the drawdown of pCO₂ in the surface waters. The Benguela Upwelling System (BUS) is a major upwelling region with one of the most productive marine ecosystems today. However, contrasting signals reported on the variation in upwelling intensities based on, for instance, foraminiferal and radiolarian indices from this region over the last glacial cycle indicate that a complete understanding of (local) changes is currently lacking. To reconstruct changes in the CO₂ history of the Northern Benguela upwelling region over the last 27 ka BP, we used a box core (64PE450-BC6) and piston core (64PE450-PC8) from the Walvis Ridge. Here, we apply various temperature and pCO₂-proxies, representing both surface (U^Kʹ ₃₇, δ¹³C of alkenones) and intermediate depth (Mg/Ca, B/Ca, S/Mg, δ¹¹B in planktonic foraminiferal shells) processes. Reconstructed pCO₂ records suggest enhanced storage of carbon at depth during the last glacial maximum. The offset between δ¹³C of planktonic (high δ¹³C) and benthic foraminifera (low δ¹³C) suggests an evidence of a more efficient biological carbon pump, potentially fuelled by remote and local iron supply through aeolian transport and dissolution in the shelf regions, effectively preventing release of the stored glacial CO₂.