Benthic barium and alkalinity fluxes: Is Ba an oceanic paleo-alkalinity proxy for glacial atmospheric CO2?

Abstract

Barium (Ba) and alkalinity (Alk) fluxes were determined from benthic chambers deployed at a variety of environments in both the Pacific and Atlantic Oceans to test if Ba and Alk fluxes from sediments differ from the current oceanic relationship. We find a benthic flux ratio (Ba/Alk ∼0.2 mmol/eq) that is significantly lower than the modern deep water trend (0.67 mmol/cq). This difference suggests that Ba is preferentially regenerated in the water column rather than from the sediments as compared to Alk. While the oceanic relationship between barium Ba and Alk has previously been used to predict the alkalinity of past oceans from Ba/Ca ratios in benthic foraminifera, our results suggest that the Ba and Alk cycles in the ocean are not coupled. This raises doubts that higher Ba/Ca ratios measured in glacial-age benthic foraminifera can be interpreted as higher glacial ocean Alk, one mechanism proposed to lower glacial atmospheric CO2.