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dc.contributor.authorGregory, Bethan S.
dc.contributor.authorClaire, Mark
dc.contributor.authorRugheimer, Sarah
dc.date.accessioned2021-03-25T16:30:01Z
dc.date.available2021-03-25T16:30:01Z
dc.date.issued2021-05-01
dc.identifier273483761
dc.identifier044bc701-35a9-4b17-acb6-d4d61278ec1c
dc.identifier85101275051
dc.identifier000631258000010
dc.identifier.citationGregory , B S , Claire , M & Rugheimer , S 2021 , ' Photochemical modelling of atmospheric oxygen levels confirms two stable states ' , Earth and Planetary Science Letters , vol. 561 , 116818 . https://doi.org/10.1016/j.epsl.2021.116818en
dc.identifier.issn0012-821X
dc.identifier.otherORCID: /0000-0001-9518-089X/work/91340952
dc.identifier.otherORCID: /0000-0003-1620-7658/work/91341004
dc.identifier.urihttps://hdl.handle.net/10023/21721
dc.descriptionThis work was supported by the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation programme (grant no. 678812 awarded to M.W.C).en
dc.description.abstractVarious proxies and numerical models have been used to constrain O2 levels over geological time, but considerable uncertainty remains. Previous investigations using 1-D photochemical models have predicted how O3 concentrations vary with assumed ground-level O2 concentrations, and indicate how the ozone layer might have developed over Earth history. These classic models have utilised the numerical simplification of fixed mixing ratio boundary conditions. Critically, this modelling assumption requires verification that predicted fluxes of biogenic and volcanic gases are realistic, but also that the resulting steady states are in fact stable equilibrium solutions against trivial changes in flux. Here, we use a 1-D photochemical model with fixed flux boundary conditions to simulate the effects on O3 and O2 concentrations as O2 (and CH4) fluxes are systematically varied. Our results suggest that stable equilibrium solutions exist for trace- and high-O2/O3 cases, separated by a region of instability. In particular, the model produces few stable solutions with ground O2 mixing ratios between 6×10-7 and 2×10-3 (3×10-6 and 1% of present atmospheric levels). A fully UV-shielding ozone layer only exists in the high-O2 states. Our atmospheric modelling supports prior work suggesting a rapid bimodal transition between reducing and oxidising conditions, and proposes Proterozoic oxygen levels higher than some recent proxies suggest. We show that the boundary conditions of photochemical models matter, and should be chosen and explained with care.
dc.format.extent12
dc.format.extent1428469
dc.language.isoeng
dc.relation.ispartofEarth and Planetary Science Lettersen
dc.subject1-D photochemical modellingen
dc.subjectAtmospheric evolutionen
dc.subjectOxygenen
dc.subjectOzoneen
dc.subjectMethaneen
dc.subjectProterozoicen
dc.subjectGE Environmental Sciencesen
dc.subjectDASen
dc.subject.lccGEen
dc.titlePhotochemical modelling of atmospheric oxygen levels confirms two stable statesen
dc.typeJournal articleen
dc.contributor.sponsorEuropean Research Councilen
dc.contributor.institutionUniversity of St Andrews. St Andrews Centre for Exoplanet Scienceen
dc.contributor.institutionUniversity of St Andrews. School of Earth & Environmental Sciencesen
dc.identifier.doihttps://doi.org/10.1016/j.epsl.2021.116818
dc.description.statusPeer revieweden
dc.identifier.urlhttps://www.sciencedirect.com/science/article/pii/S0012821X21000777?via%3Dihub#se0220en
dc.identifier.grantnumber678812en


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