Triple Oxygen Isotope Constraints on Atmospheric O₂ and Biological Productivity During the mid-Proterozoic

Authors

Peng Liu, Ocean University of China
Jingjin Liu, The Pennsylvania State University
Aoshaung Ji, The Pennsylvania State University
Christopher T. Reinhard, Georgia Institute of Technology
Noah J. Planavsky, Yale University
Dmitri Babikov, Marquette UniversityFollow
Raymond G. Najjar, The Pennsylvania State University
James F. Kasting, The Pennsylvania State University

Document Type

Article

Publication Date

12-2021

Publisher

National Academy of Sciences

Source Publication

Proceedings of the National Academy of Sciences (PNAS)

Source ISSN

0027-8424

Abstract

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 pO₂ and 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 pO₂ at that time was <1% PAL (times the present atmospheric level). Our model shows that the upper limit on pO₂ is essentially unconstrained by these data. Indeed, pO₂ levels below 0.8% PAL are possible only if atmospheric methane was more abundant than today (so that pCO₂ could 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 pCO₂ and/or improved proxies for Δ′¹⁷O of atmospheric O₂ would allow tighter constraints to be placed on mid-Proterozoic pO₂.

Comments

Published version. Proceedings of the National Academy of Sciences (PNAS), Vol. 118, No. 51 (December 15, 2021): e2105074118. DOI. © 2021 National Academy of Sciences. Used with permission.

Creative Commons License

This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.

Recommended Citation

Liu, Peng; Liu, Jingjin; Ji, Aoshaung; Reinhard, Christopher T.; Planavsky, Noah J.; Babikov, Dmitri; Najjar, Raymond G.; and Kasting, James F., "Triple Oxygen Isotope Constraints on Atmospheric O₂ and Biological Productivity During the mid-Proterozoic" (2021). Chemistry Faculty Research and Publications. 1053.
https://epublications.marquette.edu/chem_fac/1053