Increasing anthropogenic nitrogen in the North Pacific Ocean

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Science  28 Nov 2014:
Vol. 346, Issue 6213, pp. 1102-1106
DOI: 10.1126/science.1258396

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The recent increase in anthropogenic emissions of reactive nitrogen from northeastern Asia and the subsequent enhanced deposition over the extensive regions of the North Pacific Ocean (NPO) have led to a detectable increase in the nitrate (N) concentration of the upper ocean. The rate of increase of excess N relative to phosphate (P) was found to be highest (∼0.24 micromoles per kilogram per year) in the vicinity of the Asian source continent, with rates decreasing eastward across the NPO, consistent with the magnitude and distribution of atmospheric nitrogen deposition. This anthropogenically driven increase in the N content of the upper NPO may enhance primary production in this N-limited region, potentially leading to a long-term change of the NPO from being N-limited to P-limited.

Polluting the way to more productivity

Most biologically available nitrogen comes from the recycling of organic matter and nitrogen fixation. However, airborne anthropogenic nitrogen—air pollution—can also provide a source of such nitrogen. Kim et al. reconstructed changes in the N content of surface water across the North Pacific Ocean for the past four decades. N concentrations have increased markedly. This trend could enhance microbial growth in the ocean and eventually increase production of the greenhouse gas N2O.

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