Isotopic evidence of dissolved organic nitrogen production and consumption in ocean surface waters
9 affiliations
- 1Department of Geosciences, Princeton University, Princeton, NJ 08544
- 2Climate Geochemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany
- 3Division of Biosphere Sciences and Engineering, Carnegie Institution for Science, Pasadena, CA 91125
- 4Oceanography Department, Texas A&M University, College Station, TX 77843
- 5Department of Geosciences, Environment and Society, Université Libre de Bruxelles, Brussels 1050, Belgium
- 6Department of Oceanography, University of Cape Town, Rondebosch 7700, South Africa
- 7Marine and Antarctic Research Centre for Innovation and Sustainability, University of Cape Town, Rondebosch 7700, South Africa
- 8College of Marine Science, University of South Florida, St. Petersburg, FL 33701
- 9Department of Earth and Planetary Sciences, ETH Zürich, Zürich 8092, Switzerland
Abstract
Unlike dissolved inorganic nitrogen, which is scarce in much of the tropical, subtropical, and temperate surface ocean, dissolved organic nitrogen (DON) has significant concentrations and gradients. Accordingly, the lateral transport of DON may fuel biological productivity in nutrient-depleted low-latitude surface waters. Here, we report measurements of the concentration and 15N/14N ratio (δ15N) of DON in surface waters over the Pacific and Atlantic basins. DON concentration is generally highest in subpolar and equatorial waters, with minima in the subtropical gyres. A δ15N correlation is observed between surface DON and the nitrate consumed in the surface waters, indicating in situ DON production and consumption. Samples with lower DON concentrations tend to have anomalously high DON δ15N, confirming net DON transport to, and consumption in, the subtropical gyres. Net local DON production or consumption appears to dominate the observed spatial variation in the DON-to-subsurface nitrate δ15N difference. For example, N2 fixation tends to lower the δ15N of surface DON relative to subsurface nitrate mostly through encouraging DON accumulation rather than by the specific δ15N of the nitrogen introduced by N2 fixation. Unique conditions appear to apply in the equatorial Atlantic, where despite high productivity, a local minimum in DON concentration and a slight elevation in DON δ15N suggest net DON degradation. In this phosphorus-rich, nitrogen-poor upwelling environment where low iron may restrict N2 fixation, net decomposition of DON may supply needed recycled nitrogen to the ecosystem.
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BibTeX
@article{ryu2026isotopic,
title = {{Isotopic evidence of dissolved organic nitrogen production and consumption in ocean surface waters}},
author = {Yeongjun Ryu and Dario Marconi and Zhou Liang and Angela N. Knapp and François Fripiat and Sarah E. Fawcett and Patrick A. Rafter and Sergey Oleynik and Alfredo Martínez-García and Gerald H. Haug and Daniel M. Sigman},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
year = {2026},
month = oct,
doi = {10.1073/pnas.2530315123},
url = {https://doi.org/10.1073/pnas.2530315123},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Isotopic evidence of dissolved organic nitrogen production and consumption in ocean surface waters
AU - Yeongjun Ryu
AU - Dario Marconi
AU - Zhou Liang
AU - Angela N. Knapp
AU - François Fripiat
AU - Sarah E. Fawcett
AU - Patrick A. Rafter
AU - Sergey Oleynik
AU - Alfredo Martínez-García
AU - Gerald H. Haug
AU - Daniel M. Sigman
PY - 2026
DA - 2026/10/28
JO - Proceedings of the National Academy of Sciences of the United States of America
DO - 10.1073/pnas.2530315123
UR - https://doi.org/10.1073/pnas.2530315123
AB - Unlike dissolved inorganic nitrogen, which is scarce in much of the tropical, subtropical, and temperate surface ocean, dissolved organic nitrogen (DON) has significant concentrations and gradients. Accordingly, the lateral transport of DON may fuel biological productivity in nutrient-depleted low-latitude surface waters. Here, we report measurements of the concentration and 15N/14N ratio (δ15N) of DON in surface waters over the Pacific and Atlantic basins. DON concentration is generally highest in subpolar and equatorial waters, with minima in the subtropical gyres. A δ15N correlation is observed between surface DON and the nitrate consumed in the surface waters, indicating in situ DON production and consumption. Samples with lower DON concentrations tend to have anomalously high DON δ15N, confirming net DON transport to, and consumption in, the subtropical gyres. Net local DON production or consumption appears to dominate the observed spatial variation in the DON-to-subsurface nitrate δ15N difference. For example, N2 fixation tends to lower the δ15N of surface DON relative to subsurface nitrate mostly through encouraging DON accumulation rather than by the specific δ15N of the nitrogen introduced by N2 fixation. Unique conditions appear to apply in the equatorial Atlantic, where despite high productivity, a local minimum in DON concentration and a slight elevation in DON δ15N suggest net DON degradation. In this phosphorus-rich, nitrogen-poor upwelling environment where low iron may restrict N2 fixation, net decomposition of DON may supply needed recycled nitrogen to the ecosystem.
SN - 0027-8424
SN - 1091-6490
ER -