Global patterns and drivers of nitrogen isotope signal in modern marine sediments

Le résumé fourni par la source

Marine nitrogen cycle, shaped by nitrogen input and loss processes, regulates ocean productivity and leaves a distinct imprint on the ratio of stable nitrogen isotopes, δ15N. However, quantifying spatial patterns and centennial-scale variations in marine nitrogen cycling through δ15N fingerprints remains poorly constrained. Here, we present a global database of δ15N in marine sediments, comprising over 8400 seafloor samples, and create 148 time series from sediment cores spanning the past century. Our findings reveal that bulk δ15N in global marine sediments predominantly records organic matter, despite the non-negligible role of inorganic nitrogen. A widespread centennial δ15N increase, averaging 1.3‰ (interquartile range: 0.6$$-$$3.3‰) per 100 years, coinciding with total nitrogen enrichment, indicates external nitrogen inputs, productivity, and accelerated denitrification across global coastal oceans. However, in river-influenced continental margins, terrestrial sedimentary processes can obscure the 15N-enriched signal, as riverine export of 15N-depleted refractory organic matter likely lowers sedimentary δ15N. A global synthesis of marine sedimentary δ15N reveals a widespread centennial increase driven by anthropogenic nitrogen inputs and enhanced productivity, while terrestrial processes modulate this signal in river-influenced continental margins.

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