Triple oxygen isotope constraints on atmospheric O2and biological productivity during the mid-Proterozoic

Peng Liu, Jingjun Liu, Aoshuang Ji, Christopher T. Reinhard, Noah J. Planavsky, Dmitri Babikov, Raymond G. Najjar, James F. Kasting

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10 Scopus citations


Reconstructing the history of biological productivity and atmospheric oxygen partial pressure (pO2) is a fundamental goal of geobiology. Recently, the mass-independent fractionation of oxygen isotopes (O-MIF) has been used as a tool for estimating pO2and productivity during the Proterozoic. O-MIF, reported as δ'17O, is produced during the formation of ozone and destroyed by isotopic exchange with water by biological and chemical processes. Atmospheric O-MIF can be preserved in the geologic record when pyrite (FeS2) is oxidized during weathering, and the sulfur is redeposited as sulfate. Here, sedimentary sulfates from the ~1.4-Ga Sibley Formation are reanalyzed using a detailed one-dimensional photochemical model that includes physical constraints on air-sea gas exchange. Previous analyses of these data concluded that pO2at that time was <1% PAL (times the present atmospheric level). Our model shows that the upper limit on pO2is essentially unconstrained by these data. Indeed, pO2levels below 0.8% PAL are possible only if atmospheric methane was more abundant than today (so that pCO2could have been lower) or if the Sibley O-MIF data were diluted by reprocessing before the sulfates were deposited. Our model also shows that, contrary to previous assertions, marine productivity cannot be reliably constrained by the O-MIF data because the exchange of molecular oxygen (O2) between the atmosphere and surface ocean is controlled more by air-sea gas transfer rates than by biological productivity. Improved estimates of pCO2and/or improved proxies for Δ'17O of atmospheric O2would allow tighter constraints to be placed on mid-Proterozoic pO2.

Original languageEnglish (US)
Article numbere2105074118
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number51
StatePublished - Dec 21 2021

All Science Journal Classification (ASJC) codes

  • General


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