The minor sulfur isotope composition of Cretaceous and Cenozoic seawater sulfate

The last 125Myr capture major changes in the chemical composition of the ocean and associated geochemical and biogeochemical cycling. The sulfur isotopic composition of seawater sulfate, as proxied in marine barite, is one of the more perplexing geochemical records through this interval. Numerous analytical and geochemical modeling approaches have targeted this record. In this study we extend the empirical isotope record of seawater sulfate to therefore include the two minor sulfur isotopes, ³³S and ³⁶S. These data record a distribution of values around means of Δ³³S and Δ³⁶S of 0.043 ± 0.016‰ and −0.39 ± 0.15‰, which regardless of δ³⁴S-based binning strategy is consistent with a signal population of values throughout this interval. We demonstrate with simple box modeling that substantial changes in pyrite burial and evaporite sulfate weathering can be accommodated within the range of our observed isotopic values.