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Anaerobic nitrogen cycling on a Neoarchaean ocean margin

Mettam, C; Zerkle, AL; Claire, MW; Prave, AR; Poulton, SW; Junium, CK; (2019) Anaerobic nitrogen cycling on a Neoarchaean ocean margin. Earth and Planetary Science Letters , 527 , Article 115800. 10.1016/j.epsl.2019.115800. Green open access

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A persistently aerobic marine nitrogen cycle featuring the biologically mediated oxidation of ammonium to nitrate has likely been in place since the Great Oxidation Event (GOE) some 2.3 billion years ago. Although nitrogen isotope data from some Neoarchaean sediments suggests transient nitrate availability prior to the GOE, these data are open to other interpretations. This is especially so as these data come from relatively deep-water environments that were spatially divorced from shallow-water settings that were the most likely sites for the accumulation of oxygen and the generation of nitrate. Here we present the first nitrogen isotope data from contemporaneous shallow-water sediments to constrain the nitrogen cycle in shallow Late Archaean settings. The BH-1 Sacha core through the Campbellrand-Malmani carbonate platform records a transition from a shallow siliciclastic/carbonate ramp to a rimmed carbonate shelf with the potential for reduced communication with the open ocean. In these settings nitrogen isotope (δ15N) data from sub- to peri-tidal and lagoonal settings are close to 0‰, indicating diazotrophy or the complete utilization of remineralised ammonium with an isotopic composition of near 0‰. Our dataset also includes negative δ15N values that suggest the presence of an ammonium pool of concentrations sufficient to have allowed for non-quantitative assimilation. We suggest that this condition may have been the result of upwelling of phosphorus-rich deep waters into the photic zone, stimulating primary productivity and creating an enhanced flux of organic matter that was subsequently remineralised and persisted in the dominantly anoxic Neoarchaean marine environment. Notably, we find only limited evidence of coupled nitrification/denitrification, even in these shallow water environments, calling into question previous suggestions that the Late Archaean nitrogen cycle was characterized by widespread aerobic nitrogen cycling. Rather, aerobic nitrogen cycling was likely spatially heterogeneous and tied to loci of high oxygen production while zones of shallow water anoxia persisted.

Type: Article
Title: Anaerobic nitrogen cycling on a Neoarchaean ocean margin
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.epsl.2019.115800
Publisher version: https://doi.org/10.1016/j.epsl.2019.115800
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: nitrogen isotopes, carbon isotopes, Neoarchaean
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10085420
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