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Article

Abstract

Oxygen-deficient zones are hotspots of marine fixed nitrogen loss, but the temporal dynamics of their microbial processes remain poorly resolved. Here we present a nearly three-year high-resolution record from a Biogeochemical Argo float in the Eastern Tropical North Pacific that captures a decline in nitrite concentrations, reflecting a shift in nitrogen redox balance. Using a stoichiometric mass-balance model, we quantify nitrogen transformations, including dissimilatory nitrate reduction to nitrite, denitrification, anammox, and nitrite oxidation, and their coupling to carbonate chemistry. The model shows that dissimilatory nitrate reduction to nitrite dominates nitrogen transformations, while denitrification and anammox vary over depth, biogeochemical transition, and organic matter supply. Mesoscale eddies episodically modulate carbonate saturation depths horizons via isopycnal shoaling and deepening. We show that oxygen-deficient zone biogeochemistry is inherently dynamic rather than steady-state, with temporal variability in nitrogen and carbon cycling that can only be resolved through sustained autonomous observations.

Digital Object Identifier (DOI)

https://doi.org/10.1038/s43247-026-03410-5

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This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.

APA Citation

Bif, M. B., Kelly, C., Altabet, M. A., Bourbonnais, A., Elbon, C., Flores, E., Mnich, A., Plant, J., & Johnson, K. S. (2026). BGC-Argo float reveals shifts in nitrogen-carbon cycling in an oxygen-deficient zone. Communications Earth & Environment, 7.https://doi.org/10.1038/s43247-026-03410-5

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