Abstract
It is unclear why atmospheric oxygen remained trapped at low levels for more than 1.5 billion years following the Paleoproterozoic Great Oxidation Event. Here, we use models for erosion, weathering and biogeochemical cycling to show that this can be explained by the tectonic recycling of previously accumulated sedimentary organic carbon, combined with the oxygen sensitivity of oxidative weathering. Our results indicate a strong negative feedback regime when atmospheric oxygen concentration is of order pO2∼0.1 PAL (present atmospheric level), but that stability is lost at pO2<0.01 PAL. Within these limits, the carbonate carbon isotope (δ13C) record becomes insensitive to changes in organic carbon burial rate, due to counterbalancing changes in the weathering of isotopically light organic carbon. This can explain the lack of secular trend in the Precambrian δ13C record, and reopens the possibility that increased biological productivity and resultant organic carbon burial drove the Great Oxidation Event.
Highlights
It is unclear why atmospheric oxygen remained trapped at low levels for more than 1.5 billion years following the Paleoproterozoic Great Oxidation Event
Transient Proterozoic pO2 excursions cannot be ruled out by sparse data, and it has recently been suggested from a lack of chromium isotope fractionation in ironrich sedimentary rocks[14] that pO2o0.001 present atmospheric level (PAL) during 1.8–0.8 Ga
Models for Phanerozoic oxygen regulation[11,28] tend to focus on strong negative feedbacks on organic carbon burial[29], and any negative feedback on oxidative weathering is estimated to be relatively weak[30,31]. This is because near modern pO2 (B1 PAL), uplifted organic carbon is completely oxidized in slowly eroding soil environments[32], meaning oxidative weathering is transport-controlled by the supply of reduced material, rather than kinetically controlled by the pO2 level
Summary
It is unclear why atmospheric oxygen remained trapped at low levels for more than 1.5 billion years following the Paleoproterozoic Great Oxidation Event. An increase in organic carbon burial from lower values to 425% of present is sufficient to trigger the Great Oxidation Event in the model, as the net biological source of oxygen exceeds the volcanic input of reduced matter.
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