Contrasts in the marine inorganic carbon chemistry of the Benguela Upwelling System since the Last Glacial Maximum

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 which constrains the drawdown of atmospheric CO2 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 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 kyr, 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 (U37K′ and δ13C of alkenones) and subsurface (Mg / Ca and δ11B in planktonic foraminiferal shells) processes. Reconstructed pCO2 records suggest enhanced storage of carbon at depth during the Last Glacial Maximum (LGM). The offset between δ13C of planktonic (high δ13C) and benthic foraminifera (low δ13C) suggests evidence of a more efficient biological carbon pump, potentially fueled by remote and local iron supply through eolian transport and dissolution in the shelf regions, effectively preventing release of the stored glacial CO2.