1. Program on Climate Change, School of Oceanography, University of Washington, Seattle, Washington 98195, USA
2. Atmospheric and Oceanic Sciences Program, Princeton University, Princeton, New Jersey 08544, USA
3. Department of Geosciences, Guyot Hall, Princeton University, Princeton, New Jersey 08544, USA
4. IGPP and Department of Atmospheric and Oceanic Sciences, University of California at Los Angeles, Los Angeles, California 90095, USA
5. NOAA/Geophysical Fluid Dynamics Laboratory, PO Box 308, Forrestal Campus B Site, Princeton, New Jersey 08542, USA
6. Present address: Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Zurich, Switzerland.

Correspondence to: Curtis Deutsch¹ Correspondence and requests for materials should be addressed to C.D. (Email: cdeutsch@ocean.washington.edu).

Abstract

Nitrogen fixation is crucial for maintaining biological productivity in the oceans, because it replaces the biologically available nitrogen that is lost through denitrification. But, owing to its temporal and spatial variability, the global distribution of marine nitrogen fixation is difficult to determine from direct shipboard measurements. This uncertainty limits our understanding of the factors that influence nitrogen fixation, which may include iron, nitrogen-to-phosphorus ratios, and physical conditions such as temperature. Here we determine nitrogen fixation rates in the world's oceans through their impact on nitrate and phosphate concentrations in surface waters, using an ocean circulation model. Our results indicate that nitrogen fixation rates are highest in the Pacific Ocean, where water column denitrification rates are high but the rate of atmospheric iron deposition is low. We conclude that oceanic nitrogen fixation is closely tied to the generation of nitrogen-deficient waters in denitrification zones, supporting the view that nitrogen fixation stabilizes the oceanic inventory of fixed nitrogen over time.

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