What influenced the rise and fall of atmospheric oxygen during the Phanerozoic?

English Abstract:

A new reconstruction of atmospheric oxygen, which is based on the δ¹³C of terrestrial organic matter, indicates that pO₂ varied considerably during the Phanerozoic, but reached its maximum of 21% only in the recent geologic past. Throughout much of the Phanerozoic, variations in pO₂ closely followed variations in ⁸⁷Sr/⁸⁶Sr of marine carbonates, which indicates that pO₂ was primarily influenced by the rates of continental weathering and the associated burial of organic carbon and pyrite. During episodes of increased weathering, i.e., during orogenetic cycles, more sedimentary carbon and sulfur was deposited, causing a rise in pO₂. Episodes of declining pO₂, on the other hand, were primarily the result of reduced continental weathering and continuous seafloor alteration, which resulted in a constant removal of oxygen through oxidation and hydration processes. High-pO₂ episodes, including the Late Carboniferous-Early Permian and Neogene-Quaternary were characterized by low global temperatures and the presence of extensive glaciations, whereas low-pO₂ episodes were typically linked to hothouse conditions. Assuming that atmospheric carbon dioxide is the main factor that controls global temperatures, this indicates that pO₂ and pCO₂, on a long-term scale, are inversely correlated. However, short-term fluctuations of pCO₂ may have been caused by processes, such as volcanism, that had only a limited effect on the global oxygen cycle. In addition to geological factors, Phanerozoic pO₂ was also influenced by the biological evolution. The appearance of lignin in the tissue of vascular plants, for example, allowed for more efficient soil carbon storage, which ultimately led to a considerable rise in pO₂ during the Paleozoic.