An evaluation of benthic foraminiferal B/Ca and δ11B for deep ocean carbonate ion and pH reconstructions

Reliable reconstructions of deep ocean carbonate ion concentration, [CO32-], and pH are crucial to understand mechanisms responsible for the past atmospheric CO2 variations observed in ice cores. However, it is challenging to reconstruct past deep water [CO32-] and pH and literature results from different proxies conflict, warranting careful investigations on possible reasons for the existing inconsistencies. Here, we present the first down core B/Ca and delta B-11 records measured in an epifaunal benthic foraminifer Cibicidoides wuellerstorfi from the Caribbean Sea during the last 160 kyr. The two proxies yield quantitatively comparable deep water [CO32-] and pH results, showing high values during glacials relative to inter-glacials (differences in [CO32-] and pH are similar to 35 mu mol/kg and similar to 0.15, respectively), consistent with past ocean circulation changes in the Caribbean Sea. Our data provide convincing evidence that both proxies serve as faithful proxies to estimate deep ocean [CO32-] and pH, despite our incomplete understanding of boron incorporation into foraminiferal carbonates. Published by Elsevier B.V.