Stability of the marine nitrogen cycle over the past 165 million years.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 41068126.
- Also identified by DOI 10.1038/s41467-025-63604-x and PMC identifier 12511428.
- 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
Nitrogen and phosphorus are the two macro-nutrients that limit biological productivity in the ocean. While the supply of P depends on geological processes, N is biologically supplied from an inexhaustible atmospheric source, but can be limited by micro-nutrients, especially iron. Here we present a record of N and C isotopes over the past 165 Ma in marine sediments to address feedbacks between the N-cycle and productivity. Over most of the last 165 Myr, the fixed N averaged +3.2‰, (-2 and +9‰), but higher in distal areas of the ocean due to limited vertical mixing. Using an isotope box model and a coupled climate model we show that this is caused by winds that induce upwelling changing due to continental meander. Upwelling along low latitude east-west orientated Tethyan coastlines results in low δ<sup>15</sup>N, while upwelling along narrow N-S coastlines as it does today, results in high δ<sup>15</sup>N due to denitrification.