ORGANIC AND CARBONATE CARBON BURIAL THROUGH EARTH’S HISTORY

The carbonate carbon isotope record is traditionally interpreted as providing evidence of remarkable stability in the globally integrated ratio of organic to total carbon burial from Earth’s surface environments over the past ~3.8 billion years. Herein we use a terrestrial biogeochemical model coupled to a global carbon isotope mass balance to track organic carbon oxidation at varying atmospheric oxygen levels and the impact of this process on the sedimentary carbon isotope record. In strong contrast to the traditional view, we provide support for the notion of highly variable values for the organic carbon burial ratio (ƒ_org) throughout Earth’s history. We propose that the carbonate carbon isotope record has been characterized by a constant baseline value due to the linked nature of the carbon and oxygen cycles; increased organic carbon burial releases oxygen, which fuels the oxidation of organic carbon and shifts the isotopic value of the carbon entering the ocean-atmosphere system. This view of the global carbon cycle necessitates that the majority of Earth’s history was characterized by severe nutrient limitation. Further, this framework also predicts highly variable carbonate carbon isotope values during the transition to a more oxygen-rich atmosphere, providing a potential explanation for the extreme carbon isotope instability observed during the late Proterozoic and early Paleozoic.