Anomalous δ<sup>15</sup>N values in the Neoarchean associated with an abundant supply of hydrothermal ammonium.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 39984454.
- Also identified by DOI 10.1038/s41467-025-57091-3 and PMC identifier 11845595.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Unusually high δ<sup>15</sup>N values in the Neoarchean sedimentary record in the time period from 2.8 to 2.6 Ga, termed the Nitrogen Isotope Event (NIE), might be explained by aerobic N cycling prior to the Great Oxidation Event (GOE). Here we report strongly positive δ<sup>15</sup>N values up to +42.5 ‰ in ~2.75 - 2.73 Ga shallow-marine carbonates from Zimbabwe. As the corresponding deeper-marine shales exhibit negative δ<sup>15</sup>N values that are explained by partial biological uptake from a large ammonium reservoir, we interpret our data to have resulted from hydrothermal upwelling of <sup>15</sup>N-rich ammonium into shallow, partially oxic waters, consistent with uranium isotope variations. This work shows that anomalous N isotope signatures at the onset of the NIE temporally correlate with extensive volcanic and hydrothermal activity both locally and globally, which may have stimulated primary production and spurred biological innovation in the lead-up to the GOE.