A revised seawater sulfate oxygen isotope record for the last 4Â Myr

Using a new method to purify barium sulfate from marine barite, we produce a highly resolved seawater sulfate oxygen isotope data set for the past 4 million years. We show that the overall magnitude of the δ18O shift is smaller than previously thought (1-1.5‰ vs 6 ‰).Expanding on previous work, we explore the effects of Quaternary sea level variations on the global sulfur cycle. Our modeling results confirm the earlier hypothesis that the increased duration and amplitude of sea level lowstands during the Quaternary favors direct sulfide oxidation over microbial disproportionation.We show that oxygen isotope ratios of core top barite are up to 2.5‰ lower than the seawater sulfate δ18O value. We hypothesize that this offset is caused by incorporation of sulfate from oxidized organic sulfur compounds during precipitation of barite. Our results provide another puzzle piece in the attempt to understand the origin of marine barite.