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Examining Archean methanotrophy

Slotznick, Sarah P. and Fischer, Woodward W. (2016) Examining Archean methanotrophy. Earth and Planetary Science Letters, 441 . pp. 52-59. ISSN 0012-821X. doi:10.1016/j.epsl.2016.02.013.

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The carbon isotope ratios preserved in sedimentary rocks can be used to fingerprint ancient metabolisms. Organic carbon in Late Archean samples stands out from that of other intervals with unusually low δ^(13)C values (∼−45 to −60‰). It was hypothesized that these light compositions record ecosystem-wide methane cycling and methanotrophy, either of the aerobic or anaerobic variety. To test this idea, we studied the petrography and carbon and oxygen isotope systematics of well-known and spectacular occurrences of shallow water stromatolites from the 2.72 Ga Tumbiana Formation of Western Australia. We examined the carbonate cements and kerogen produced within the stromatolites, because methanotrophy is expected to leave an isotopic fingerprint in these carbon reservoirs. Mathematical modeling of Archean carbonate chemistry further reveals that methanotrophy should still have a discernible signature preserved in the isotopic record, somewhat diminished from those observed in Phanerozoic sedimentary basins due to higher dissolved inorganic carbon concentrations. These stromatolites contain kerogen with δ^(13)C_(org) values of ∼−50‰. By microsampling different regions and textures within the stromatolites, we determined that the isotopic compositions of the authigenic calcite cements show a low degree of variation and are nearly identical to values estimated for seawater at this time; the lack of low and variable δ^(13)C_(carb) values implies that methanotrophy does not explain the low δ^(13)C_(org) seen in the coeval kerogen. These observations do not support a methanotrophy hypothesis, but instead hint that the Late Archean may constitute an interval wherein autotrophs employed markedly different biochemical processes of energy conservation and carbon fixation.

Item Type:Article
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URLURL TypeDescription
Slotznick, Sarah P.0000-0001-8374-3173
Fischer, Woodward W.0000-0002-8836-3054
Additional Information:© 2016 Elsevier B.V. Received 1 October 2015; Received in revised form 10 January 2016; Accepted 5 February 2016. Support for this work was provided by the Agouron Institute (grant number AI-GC17.09.3), NSF Division of Earth Sciences award EAR-1349858, the NSF Graduate Research Fellowship program (S.P.S.), NASA Earth and Space Fellowship (S.P.S.), and the David and Lucile Packard Foundation (W.W.F.). Thanks to John Grotzinger, Renata Cummins, Daniel Stolper and Kristin Bergmann for helpful comments and aid with clumped isotope measurements. We also thank John Higgins, Itay Halevy, David Fike, and two anonymous reviewers for helpful feedback that substantially improved the quality of the study.
Funding AgencyGrant Number
Agouron InstituteAI-GC17.09.3
NSF Graduate Research FellowshipUNSPECIFIED
NASA Earth and Space Science FellowshipUNSPECIFIED
David and Lucile Packard FoundationUNSPECIFIED
Subject Keywords:stromatolite; C isotopes; clumped isotopes; anaerobic oxidation of methane; reductive acetyl-CoA pathway
Record Number:CaltechAUTHORS:20160310-075642470
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Official Citation:Sarah P. Slotznick, Woodward W. Fischer, Examining Archean methanotrophy, Earth and Planetary Science Letters, Volume 441, 1 May 2016, Pages 52-59, ISSN 0012-821X, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:65251
Deposited By: Tony Diaz
Deposited On:10 Mar 2016 19:24
Last Modified:10 Nov 2021 23:42

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