The methods on how the samples were collected and processed for the attached dataset can be found in the methodology section of Flynn et al. (2019).\u00a0
\nHydrographic measurements were made using a conductivity-temperature-depth (CTD) profiler fitted with a temperature, salinity and oxygen sensor.\u00a0
\nNitrate+nitrite concentrations were measured following published auto-analysis protocols (Diamond 1994; Grasshoff 1976), and nitrite and phosphate concentrations were determined using benchtop colourimetric methods (Strickland and Parsons 1968; Bendschneider and Robinson 1952; Parsons et al. 1984).\u00a0
\nNitrate N and O isotope ratios were measured using the \u201cdenitrifier method\u201d (Sigman et al. 2001; Casciotti et al. 2002; McIlvin and Casciotti 2011).
\nSeawater samples were collected at discrete depths from the surface to the seafloor using a tethered rosette holding twelve 6-L Niskin bottles. At each CTD station, nutrient and nitrate isotope samples were collected filtered (0.22 \u00b5m PES membrane syringe filter) throughout the water column in 60 mL HDPE bottles. Each bottle was rinsed three times prior to being filled, and then immediately frozen at -20\u00b0C pending analysis. All nutrient samples were analysed within a year from collection, and nitrate isotopes within 18 months of collection.\u00a0
CTD data:
\nThe temperature and conductivity probes are calibrated annually by the manufacturer while the oxygen sensor was calibrated against discrete seawater samples analyzed for dissolved oxygen concentrations by Winkler titration (Carpenter 1965; Grasshoff et al. 1983).
Nutrients:
\nDuplicate samples were measured for nitrate+nitrite on different days, and the standard deviation for duplicates was <0.5 \u00b5M, with a lower standard deviation for lower concentration samples
\nDuplicate samples for phosphate and nitrite were measured in duplicate on different days of analysis, yielding a standard deviation for duplicates of \u22640.1 \u00b5M.\u00a0
Nitrate isotopes:
\nThe N and O isotope ratios of nitrate were measured in triplicate in separate batch analyses and standard deviations for both \u03b415N and \u03b418O were <0.3\u2030. Certified nitrate isotope ratio reference materials in nutrient-free seawater were measured in all batch analyses. These included IAEA-NO3-, with \u03b415N of 4.7 \u00b1 0.2\u2030 vs. N2 air (Gonfiantini et al. 1995) and and \u03b418O of 25.6 \u00b1 0.4\u2030 vs. VSMOW (B\u00f6hlke et al. 2003), and USGS-34, with \u03b415N of -1.8 \u00b1 0.1\u2030 vs. N2 air and \u03b418O of -27.9 \u00b1 0.3\u2030 vs. VSMOW (B\u00f6hlke et al. 2003). Nitrate isotstandards in individual runs were diluted in nutrient-free seawater to concentrations similar to those of the samples to account for potential matrix effects on the \u03b418O measurements (Weigand et al. 2016). Reproducibility was monitored by analysis of an internal seawater nitrate standard from the deep North Atlantic.
BCO-DMO Processing Notes:
\n-\u00a0added conventional header with dataset name, PI name, version date
\n- modified parameter names to conform with BCO-DMO naming conventions
\n- converted positive latitude values for SHGML005 in May 2017 to negative values as they were incorrect.
\n- removed extra data row at bottom of Aug sheet.