The isotopic ratio of dissolved nitrogen (15N/14N) in seawater has been measured at 147 stations covering depths from 3 m to 5000 m (Malaspina 2010 expedition). A total of 1488 gas samples were analyzed. The δ15N values range between -0.18 ‰ and + 0.34 ‰ (AIR), with a mean value of +0.07 ‰ (AIR). Dissolved surface N2 (3 m depth) has a mean value of δ15N ‰ = -0.01 vs AIR. Samples taken at depths of 3000 m and 5000 m, have a mean value of +0.13 vs AIR (n = 183). The Atlantic, Indian and Pacific have similar mean isotopic values, with noticeably more positive values in the Pacific zone between Hawaii and Panama Pacific, coinciding with oxygen minimum zones (OMZs). Despite the small range of global variation of the δ15N values, trends are observed in the profiles from the surface to the DCM. Also noteworthy are the changes related to oxygen minimum zones, which are probably related to denitrification or anammox processes contributing to major losses of fixed nitrogen as dinitrogen (N2) which has a different isotopic footprint

Aquatic Sciences Meeting, Aquatic Sciences: Global And Regional Perspectives - North Meets South, 22-27 February 2015, Granada, Spain

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