An isotopically light nitrogen reservoir in the ocean : evidence from ferromanganese crusts
Abstract
Ferromanganese (FeMn) oxide crusts and nodules in the deep ocean have been studied extensively in the context of critical metals and metal isotope mass balances; however, their role in the marine nitrogen cycle has been unexplored. Here we investigated a suite of hydrogenetic and diagenetic marine FeMn crusts and nodules from the Pacific to determine their isotopic signature and contribution as another N sink from the modern ocean. Our results reveal unusually low δ15N values down to −12 ‰ in some hydrogenetic crusts, paired with low δ13C values in carbonate associated with these crusts and nodules. This pattern is most parsimoniously explained by partial oxidation of ammonium (nitrification) derived from benthic biomass. Nitrification generates isotopically light nitrite, which may adhere to FeMn oxides by adsorption. In contrast, the diagenetic and hydrogenetic nodules are enriched in 15N/14N to up to +12 ‰, likely due to retention of ammonium in phyllosilicate minerals. Overall, we conclude that FeMn oxide crusts and nodules are a novel archive of microbial activity that may be preserved in the sedimentary record on Earth and possibly Mars.
Citation
Stueeken , E E & Bau , M 2023 , ' An isotopically light nitrogen reservoir in the ocean : evidence from ferromanganese crusts ' , Geochemical Perspectives Letters , vol. 25 , pp. 13-17 . https://doi.org/10.7185/geochemlet.2308
Publication
Geochemical Perspectives Letters
Status
Peer reviewed
ISSN
2410-339XType
Journal article
Description
Funding: UK Nature Environment Research Council NERC (grant NE/V010824/1); Deutsche Forschungsgemeinschaft (DFG SPP1833 grant BA-2289/8-1).Collections
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