Water column nitrate+nitrite d15N measurements from R/V L'Atalante in the southwest Pacific Ocean between New Caledonia and Tahiti from February to March 2015

Abstract

Constraining the rates and spatial distribution of di-nitrogen (N2) fixation fluxes to the ocean informs our understanding of the environmental sensitivities of N2 fixation as well as the timescale over which the fluxes of nitrogen (N) to and from the ocean may respond to each other. Here we quantify rates of N2 fixation as well as its contribution to export production along a zonal transect in the Western Tropical South Pacific (WTSP) Ocean using N isotope (“d15N”) budgets. Comparing measurements of water column nitrate+nitrite d15N with the d15N of sinking particulate N at a western, central, and eastern station, these d15N budgets indicate high, modest, and low rates of N2 fixation at the respective stations. The results also imply that N2 fixation supports exceptionally high, i.e., >50%, of export production at the western and central stations, which are also proximal to the largest iron sources. These geochemically-based rates of N2 fixation are equal to or greater than those previously reported in the tropical North Atlantic, indicating that the WTSP Ocean has the capacity to support globally significant rates of N2 fixation, which may compensate for N removal in the oxygen deficient zones of the eastern tropical Pacific. For a complete list of measurements, refer to the supplemental document 'Field_names.pdf', and a full dataset description is included in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: http://www.bco-dmo.org/dataset/733237