Some water samples were collected by Niskin bottle on a CTD rosette ("CTD profile"), while others were collected using a trace metal clean "Towfish" that was running along side the ship and collected trace metal clean underway samples ~1 m below the sea surface.

NO3-+NO2- d15N and d18O and TDN δ15N analysis was by the "denitrifier method" and followed the methods described by Sigman et al., 2001, Casciotti et al., 2002, McIlvin and Casciotti, 2011, and Weigand et al., 2016. Briefly, NO3-+NO2- was quantitatively reduced to N2O by Pseudomonas aureofaciens and Pseudomonas chlororaphis, which was then cryogenically focused and analyzed on an isotope ratio mass spectrometer. A volume of sample was added to each bacterial vial to achieve a final quantity of 10 or 20 nmols N2O, which was then purged from the vial using a helium carrier gas. The d15N of N2O in samples was calibrated with the international isotopic reference materials

The δ15N of TDN was measured using persulfate oxidation of DON to NO3- followed by the denitrified method as described in Knapp et al. (2005).

Nitrate+nitrite concentration was measured by others (Karl lab, U. Hawaii) using colorimetric methods, and total dissolved nitrogen concentration was measured by others (Karl lab, U. Hawaii) using uv-oxidation and subsequent colorimetric analysis. Both of these data sets can be found at: http://scope.soest.hawaii.edu/data/