Dataset: Tropical Pacific nitrate nitrogen and oxygen isotopes

Sampling and Analytical Methodology:
Nitrate isotope measurements were performed using the “Denitrifier” method (Sigman et al. 2001; Casciotti et al. 2002). Measurements are referenced to atmospheric N2 or Vienna Standard Mean Ocean Water, respectively. The analytical precision was 0.2 per mil for nitrate N isotopes and 0.3 per mil for nitrate O isotopes based on a seawater-based, in-house standard included in every batch of analyses. Nitrite was removed from all samples using the protocol of Granger and Sigman (2009). Nitrate concentrations were measured by reduction to NO using a vanadium(III) reagent, followed by chemiluminescence measurement of NO (Braman and Hendrix 1989). Hydrographic data (salinity, temperature, and oxygen) for each cruise were acquired from NOAA’s Pacific Marine Environmental Laboratory data portal (www.epic.noaa.gov). Acoustic Doppler Current Profiler (ADCP) measurements for the upper 200 m were available for most stations (with the notable exception of the boreal spring 2005 cruise along 1108W) and are available through the University of Hawai’i (currents.soest.hawaii.edu).