Abstract
Oxygen and carbon are 2 elements critical for life on Earth. Earth's most dramatic oxygenation events and carbon isotope excursions (CIE) occurred during the Proterozoic, including the Paleoproterozoic Great Oxidation Event and the associated Lomagundi CIE, the Neoproterozoic Oxygenation event, and the Shuram negative CIE during the late Neoproterozoic. A specific pattern of a long-lived positive CIE followed by a negative CIE is observed in association with oxygenation events during the Paleo- and Neo-proterozoic. 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 δ(13)C of volcanic CO(2) 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 O(2) accumulation, while positive CIEs are driven by rapid release of subducted carbonate-derived CO(2) at arcs. The subsequent negative CIEs are driven by the delayed release of organic C-derived CO(2) at ocean islands. Our model reproduces the sequences observed in the Paleo- and Neo-proterozoic, that is oxygenation accompanied by a positive CIE followed by a negative CIE. 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.