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Oxygen and carbon are two elements critical for life on Earth. Earth's most dramatic oxygenation events and carbon isotope excursions occurred during the Proterozoic, including the Paleoproterozoic Great Oxidation Event and the associated Lomagundi carbon isotope excursion, the Neoproterozoic Oxygenation event, and the Shuram negative carbon isotope excursion during the late Neoproterozoic. A specific pattern of a long-lived positive carbon isotope excursion followed by a negative carbon isotope excursion is observed in association with oxygenation events during the Paleo- and Neoproterozoic. We present results from a carbon cycle model designed to couple the surface and interior cycling of carbon that reproduce this pattern. The model assumes organic carbon resides in the mantle longer than carbonate, leading to systematic temporal variations in the δ13C of volcanic CO2 emissions. When the model is perturbed by periods of enhanced continental weathering, increased amounts of carbonate and organic carbon are buried. Increased deposition of organic carbon allows O2 accumulation, while positive carbon isotope excursions are driven by rapid release of subducted carbonate-derived CO2 at arcs. The subsequent negative carbon isotope excursions are driven by the delayed release of organic C-derived CO2 at ocean islands. Our model reproduces the sequences observed in the Paleo- and Neoproterozoic, that is, oxygenation accompanied by a positive carbon isotope excursion followed by a negative carbon isotope excursion. Periods of enhanced weathering correspond temporally to supercontinent break-up, suggesting an important connection between global tectonics and the evolution of oxygen and carbon on Earth.

Proterozoic supercontinent break-up as a driver for oxygenation events and subsequent carbon isotope excursions