Empirical partition coefficients for Sr and Ca in marine barite: Implications for reconstructing seawater Sr and Ca concentrations

A robust record of fluctuations in seawater Sr and Ca concentrations is critical for understanding the long‐term global carbon cycle as it is influenced by the history and location of carbonate precipitation, chemical weathering, and hydrothermal activity. Such a record is also necessary for interpretation of paleoceanographic records (temperature, productivity) derived from carbonate sources (e.g. Sr/Ca, Mg/Ca, Li/Ca). Marine barite, an inorganic phase preserved in oxic, deep‐sea sediments, may record seawater Sr and Ca concentrations. Using core top barite samples we have derived the partition coefficients for Sr (DSr = 2.9 × 10−5), Ca (DCa = 1.9 × 10−8), and Sr/Ca (DSr/Ca = 1.6 × 103) in barite. The natural variability of core top marine barite Sr/Ca, Sr/Ba, and Ca/Ba ratios, selected from different ocean basins, is 10.1%, 15.0%, and 16.3%, respectively. Since estimates of Cenozoic fluctuations in seawater Sr/Ca ratios are large (possibly greater than 80%) relative to the variability recorded in core tops, marine barite may be used to reconstruct seawater Sr/Ca ratios, and Sr and Ca concentrations, using empirically derived partition coefficients.