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The supply of excess phosphate across the Gulf Stream and the maintenance of subtropical nitrogen fixation

Author(s): Palter, Jaime B; Lozier, MS; Sarmiento, Jorge L; Williams, Richard G

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Abstract: The subtropical North Atlantic is considered a hot spot for biological nitrogen fixation, with estimated rates between 1 and 20 × 1011 mol nitrogen fixed annually. However, the region's nutrient reservoir beneath the euphotic zone is so enriched in nitrate relative to phosphate that it is perplexing how fixation might be sustained there. Here, we investigate whether the physical transport of excess phosphate into the subtropical gyre is sufficient to sustain nitrogen fixation in the gyre. Specifically, we assess the Ekman advection and isopycnal mixing of excess phosphate to the subtropical North Atlantic, using detailed hydrographic and nutrient sections occupied across the Gulf Stream combined with satellite wind data. Ekman advection and along‐isopycnal mixing provide a source of approximately 2 × 1010 mol yr−1 of excess phosphate in the northwestern subtropics, a physical mechanism that has the potential to support more than 3 × 1011 mol yr−1 of biological nitrogen fixation, after accounting for alternative sinks of excess phosphate. This excess phosphate supply across the gyre's northern boundary and high nitrogen fixation there offers a mechanism that can explain both the maintenance of subtropical North Atlantic nitrogen fixation in a phosphate‐poor environment and help account for the weak gradients in the proxies of fixation observed along interior circulation pathways of the gyre.
Publication Date: 3-Nov-2011
Citation: Palter, Jaime B., M. Susan Lozier, Jorge L. Sarmiento, and Richard G. Williams. "The supply of excess phosphate across the Gulf Stream and the maintenance of subtropical nitrogen fixation." Global Biogeochemical Cycles 25, no. 4 (2011). doi:10.1029/2010GB003955.
DOI: doi:10.1029/2010GB003955
ISSN: 0886-6236
EISSN: 1944-9224
Type of Material: Journal Article
Journal/Proceeding Title: Global Biogeochemical Cycles
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.

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