| Summary: | Constraining the rates and spatial distribution of dinitrogen (N-2) fixation fluxes to the ocean informs our understanding of the environmental sensitivities of N-2 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 N-2 fixation as well as its contribution to export production along a zonal transect in the western tropical South Pacific (WTSP) Ocean using N isotope ("delta N-15") budgets. Comparing measurements of water column nitrate + nitrite delta N-15 with the delta N-15 of sinking particulate N at a western, central, and eastern station, these delta N-15 budgets indicate high, modest, and low rates of N-2 fixation at the respective stations. The results also imply that N-2 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 N-2 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 N-2 fixation, which may compensate for N removal in the oxygen-deficient zones of the eastern tropical Pacific.
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