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Updated: Jul 26, 2026

Seawater Sampling and Collection
Published on: June 17, 2009
Calibration of sulfate levels in the archean ocean
Kirsten S Habicht1, Michael Gade, Bo Thamdrup
1Danish Center for Earth System Science and Institute of Biology, University of Southern Denmark, Campusvej 55, DK-5230, Odense M, Denmark.
Abstract:
The size of the marine sulfate reservoir has grown through Earth's history, reflecting the accumulation of oxygen into the atmosphere. Sulfur isotope fractionation experiments on marine and freshwater sulfate reducers, together with the isotope record, imply that oceanic Archean sulfate concentrations were <200 microM, which is less than one-hundredth of present marine sulfate levels and one-fifth of what was previously thought. Such low sulfate concentrations were maintained by volcanic outgassing of SO2 gas, and severely suppressed sulfate reduction rates allowed for a carbon cycle dominated by methanogenesis.
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