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A quantitative comparison of the physical supply and biological uptake of new nitrogen in the Arctic Ocean

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Abstract

Nitrogen constrains biomass across the Arctic Ocean, with nitrate (NO3) supply to the surface waters fuelling new primary production and net carbon drawdown. In this Review, we explore the physical mechanisms driving NO3 fluxes to the euphotic zone across the Arctic Ocean and how biological processes respond. The volume and inflow depth of Atlantic and Pacific Ocean waters, together with sea ice and halocline dynamics, govern internal physical mixing of NO3. Respectively, these inflows supply ~34 ± 5 kmol NO3 s−1 and 9 ± 1 kmol NO3 s−1, spreading at mid-depth. NO3 from below the euphotic zone is mixed upwards via several mechanisms. Overall, NO3 fluxes associated with diffusive and turbulent mixing, submesoscale fronts and cyclonic mesoscale eddies are relatively low (on the order of ~0.1–0.7 mmol m−2 per day) but cover a large area, with peaks associated with wind events or individual strong eddies. By comparison, upwelling-driven fluxes are much stronger (on the order of ~1 mmol m−2 per day) but are more localized. Near-inertial and tidal mixing over the Arctic Ocean’s complex bathymetry drives perhaps the strongest NO3 fluxes, for example, reaching 4.5 mmol m−2 per day in the Barents Sea. Comparing these fluxes with observed biological NO3 uptake rates indicates that the internal physical supply of NO3 only limits primary productivity in 9 of the 17 cases considered. Thereafter, light limitation and lagged growth responses can result in excess NO3 remaining in the surface waters. Future research should prioritize linking NO3 supply and uptake at corresponding spatiotemporal scales.

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Fig. 1: Surface currents and summer surface nitrate concentrations in the Arctic Ocean.
Fig. 2: Characteristics and factors influencing stratification across the Arctic Ocean.
Fig. 3: Inferring nitrate limitation of primary production from observations.
Fig. 4: Physical nitrate fluxes of varying scales and magnitude.
Fig. 5: Double diffusion in a quiescent region of the Arctic Ocean.
Fig. 6: The range of physical processes driving nitrate fluxes from Pacific water, Atlantic water or terrigenous sources into the euphotic zone of the Arctic Ocean.

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Acknowledgements

The authors thank P. Wassmann (University of Tromsø) for facilitating the workshop in Motovun, Croatia, where this Review was conceptualized, and C. Oldham (UWA, Australia) for instigating the original discussions regarding the use of the Damköhler Number. A.M.W. and A.L. thank the Canada First Research Excellence Fund through the Ocean Frontier Institute for financial support. S.L.D. thanks NSF award OPP-2053084: Collaborative research: taking the pulse of the Arctic Ocean — a US contribution to the International Synoptic Arctic Survey for support. A.R. thanks the INSPIRES programme of the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research under the framework of Helmholtz Research Program ‘Changing earth — sustaining our future’ (PoF IV), the DFG Priority Program SPP 1158 ‘Antarctic research with comparative investigations in Arctic ice areas’ (project number 562122740) and a Visiting Fellowship funded by the Ocean Frontier Institute and OFI and the Canada First Research Excellence Fund for financial support. L.O. thanks the German Federal Ministry of Education and Research (BMBF) for the nuArctic project (grant 03F0918A) for financial support.

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Authors and Affiliations

  1. Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany

    Anya M. Waite, Laurent Oziel, Benjamin Rabe, Andreas Rogge, Sinhué Torres-Valdés, Sarah-Sophie Weil & Wilken-Jon von Appen

  2. Oceanography Department and Ocean Frontier Institute, Dalhousie University, Halifax, Nova Scotia, Canada

    Anya M. Waite & Alice Lane

  3. Institute of Ocean Sciences, Department of Fisheries and Oceans, Sidney, British Columbia, Canada

    Eddy Carmack

  4. College of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Fairbanks, AK, USA

    Seth L. Danielson

  5. SINTEF Ocean, Trondheim, Norway

    Ingrid Ellingsen

  6. Geophysical Institute, University of Bergen and Bjerknes Centre for Climate Research, Bergen, Norway

    Ilker Fer

  7. School of Ocean Sciences, Bangor University, Bangor, UK

    Yueng-Djern Lenn

  8. Akvaplan-niva AS, Fram Centre, Tromsø, Norway

    Achim Randelhoff

  9. Minderoo Foundation, Broadway, Nedlands, Australia

    Eric J. Raes

  10. The UWA Oceans Institute, The University of Western Australia, Crawley, Western Australia, Australia

    Eric J. Raes

  11. Institute of Environmental Physics, University of Bremen, Bremen, Germany

    Andreas Rogge

  12. Québec-Océan and Université Laval, Québec, Canada

    Jean-Éric Tremblay

  13. Biodiversity, Macroecology and Biogeography, University of Göttingen, Göttingen, Germany

    Sarah-Sophie Weil

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Contributions

A.M.W. conceptualized and led the article. A.L. led the data synthesis. All authors contributed to discussions and the writing of the paper.

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Correspondence to Anya M. Waite.

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Supplementary information

Glossary

Barotropic

The horizontal ocean velocity is mostly depth-independent.

Denitrification

A microbially driven process whereby specialized anoxic bacteria use nitrate (NO3) as an electron acceptor to oxidize organic matter, yielding N2 and N2O.

Diffusive layering

Similar to salt fingering, these intrusions occur owing to the difference in diffusion rates between heat and salt, but diffusive layering occurs where cool fresh water overlays warm salty water.

Eddy kinetic energy

A measure for the variability of the flow field on timescales of days to weeks owing to, for example, eddies, meanders and storm-induced motions.

Euphotic zone

The upper tens of metres of the ocean in which there is enough light for phytoplankton to grow.

Freshet

High seasonal water flow through rivers as a result of snow and/or ice melt.

Halocline

The strong vertical gradient in salinity, which in the Arctic Ocean typically ranges from ~30 practical salinity units (psu) to ~35 psu and occurs between 50 m and 300 m depth, generally overlapping with the pycnocline.

Inertial frequency

Also known as the Coriolis parameter, f = 2Ω sinΦ, in which the inertial frequency, f, is in radians per second, Ω is the angular velocity of the Earth’s rotation (~7.2921 × 10−5 rad s−1) and Φ is the latitude.

Internal wave

A gravity wave that oscillates in a stratified fluid.

Mesoscale eddies

Approximately circular motion of water with a radius similar to the Rossby radius (~10 km in the Arctic Ocean); the horizontal velocities are in geostrophic balance and the associated vertical velocities are small.

Near-inertial waves

Internal gravity waves with a frequency near the local inertial frequency, f (Coriolis parameter).

Nitracline

The vertical range in the ocean over which the nitrate concentration strongly increases; in the Arctic Ocean, this often is tightly linked to the halocline.

Nitrification

The oxidation of ammonia (NH3) to nitrate (NO3) via ammonia oxidizing archaea and bacteria.

Nitrogen fixation

The enzymatic conversion of atmospheric N2 to ammonia (NH3) by diazotrophs.

Salt fingering

Instabilities or salt fingers across a density interface that occur when warm salty water overlays cool fresh water (salinity is not stably stratified), because heat diffuses faster than salt.

Tidal frequencies

The frequency of fundamental tidal constituents such as M2, the principal lunar semidiurnal constituent with a period of about 12.42 h, or K1, a luni-solar diurnal constituent with a period of 23.93 h. There are four semidiurnal and four diurnal fundamental frequencies.

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Waite, A.M., Lane, A., Carmack, E. et al. A quantitative comparison of the physical supply and biological uptake of new nitrogen in the Arctic Ocean. Nat Rev Earth Environ (2026). https://doi.org/10.1038/s43017-026-00769-z

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