Boron/calcium ratios in Globigerinoides ruber from the Arabian Sea: Implications for controls on boron incorporation

Abstract

Culture and downcore studies have been used to argue that B/Ca ratios in planktic foraminifera are correlated with seawater pH and may record seawater borate/bicarbonate ratios, although other factors may also control B/Ca. Specimens of Globigerinoides ruber from the Ocean Drilling Program (ODP) Site 723A (western Arabian Sea) and Core AAS9/21 (eastern Arabian Sea) from the last 22 kyr were analysed for B/Ca, delta¹⁸O and Mg/Ca. B/Ca was compared to reconstructed salinity and sea surface temperature (SST) records, to gain insight into the processes controlling the incorporation of boron. In both cores, B/Ca and Mg/Ca are positively correlated which suggests that temperature governs the incorporation of boron in G. ruber to some extent. Higher B/Ca ratios at the site affected by upwelling (ODP 723A) than in the non-upwelling region (Core AAS9/21), and a positive correlation between B/Ca and shell size in G. ruber are observed. We observe no significant correlation between B/Ca in G. ruber and salinity, pH or dissolved inorganic carbon (DIC) in either the western or eastern Arabian Sea which throws considerable doubt on the utility of B/Ca ratios as a pH or pCO₂ proxy.