Nitrate isotope data from R/V Thomas G. Thompson cruise TN303 in the Eastern Tropical Pacific in 2013 (U.S. GEOTRACES EPZT project) (NCEI Accession 0278415)

Acquisition Description:
Sampling : Full depth and super station samples were collected from the ship's rosette. Samples were filtered through 0.8/0.45 um acropak5 00 filter cartridges into triple-rinsed 60 mL HDPE bottles. Demi station samples were collected from the GETORACES Go-Flo rosette. Samples were filtered through 0.2 um acropak capsule filters into triple-rinsed 60 mL HDPE bottles. Each sample was collected in triplicate. Samples were frozen at -20 C immediately and stored frozen until analysis.

Analysis : Samples were analyzed for nitrate d15N using the denitrifier method (Sigman et al., 2001; Casciotti, et al., 2001, with technical updates described by McIlvin and Casciotti, 2011). In the Casciotti Lab, Nitrate isotope reference materials USGS32 and USGS34 were used to calibrate d15N. Each sample was analyzed 2-6 times. Mean and standard deviations are reported for each sample. Samples were analyzed either on a DeltaPLUS XP or DeltaV PLUS isotope ratio mass spectrometer (IRMS), both with custom-built inlets described in McIlvin and Casciotti, 2011. Where possible (concentrations exceeded 2 uM), samples and standards were analyzed in 20 nanomole aliquots. When NO3- concentrations were below 2 uM, samples were injected in maximum volume (10 mL) and calibrated using interpolations between standard curves of 5 and 20 nano moles NO3-. Samples containing nitrate concentrations lower than 0.3 uM were not analyzed. Samples containing measurable NO2- concentrations were treated with sulfuric acid prior to analysis (Granger and Sigman, 2009).