The sulphur isotopic evolution of Neoarchean and Paleoproterozoic seawater - clues for reconstructing Earth's oxygenation and sulphur metabolism

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It is commonly accepted that Earth s atmosphere and ocean have experienced a substantial increase in oxygen abundance in the early Paleoproterozoic (the Great Oxidation Event - G.O.E.). It has further been demonstrated that changes in atmospheric composition and the timing of this G.O.E. can be constrained by multiple sulphur isotope measurements (32S, 33S, 34S, 36S), recording mass independent sulphur isotope fractionation. Among other aspects, the increase in atmospheric oxygen must have been paralleled by an increase in oceanic sulphate abundance. This in turn should have stimulated microbial sulphur metabolism. The sulphur isotopic composition of seawater sulphate provides an excellent proxy for changes within the global sulphur cycle. Specifically, microbial turnover of oceanic sulphate, a process associated with substantial isotope fractionation, is recorded by an increase in (34SSO4 In the absence of respective data, a temporal record for the sulphur isotopic composition of seawater sulphate through the Neoarchean-Paleoproterozoic transition will be obtained. For this, trace sulphate in carbonates from the respective South African succession will be studied.