Dataset: GN01 Snow NO3 NH4 H2O

NOTES: Not enough nitrate for D17O analysis. Ammonium concentrations were below detection for stations 43 and 46. Due to low concentrations/no detectable ammonium, no icehole seawater samples were measured for d15N-NH4. Sample 59 had no sample left to conduct NH4 or H2O isotope sample analysis. Of the sample volume available and concentration, only two snow samples were measured for d15N-NH4.

As described in Kaiser et al. (2007), isotopic data is corrected and standardized to international reference materials IAEA-N3, USGS34, and USGS35, which are run 3-9 times with each sample run. For d15N, samples are corrected for isobaric interferences and a blank associated with the bacteria. For d18O, samples are corrected for isobaric interferences, blank, and exchange between sample nitrate and background water that takes place during denitrification to nitrous oxide. The pooled standard deviation for the reference materials are (n=88): 0.2 per mil for d15N and 0.7 per mil for d18O of IAEA-N3; 0.3 per mil for d15N and 0.7 per mil for d18O of USGS34; and 0.7 per mil for d18O of USGS35 (sample d15N is not corrected for d15N of USGS35, this is used as an internal quality check and pooled standard deviation across all runs in 0.2 per mil). 10 samples were run in duplicate or triplicate and the paired pooled standard deviation (n=10) is 0.2 per mil for d15N and 0.4 per mil for d18O. Pooled standard deviation for USGS34 and USGS35 run for D17O is 0.6 and 0.9 per mil each (n=14 and 15, respectively), and replicate samples were 0.9 per mil (n=4).

Due to low sample volume and concentrations, only 3 samples were analyzed for d15N-NH4 using hypobromite oxidation to nitrite coupled with the denitrifier method (Felix et al., 2013; Zhang et al., 2007; Sigman et al., 2001). Briefly, ammonium is oxidized to nitrite with hypobromite, and nitrite is quantitatively converted to nitrous oxide with denitrifying bacteria. For the three samples with sufficient analyte, oxidations were conducted in triplicate. Samples were calibrated using ammonium reference materials USGS25 and IAEA-N2. Precision for d15N-NH4 of reference materials was ≤ 2.7 per mil and based on the standard deviation of reference replicates. The d15N-NH4 is then computed from the weighted difference from d15N-NO3.

Oxygen and hydrogen isotope ratios of water (d18O-H2O vs. VSMOW, dD-H2O vs. VSMOW) were measured using wavelength-scanned cavity-down ring spectroscopy on a Picarro L1102-I liquid analyzer calibrated to international reference standards USGS46, USGS49 and VSMOW. Raw data are corrected for memory and drift effects followed by normalization using a standard calibration (Vaughn and Claymoore, INSTAAR, University of Colorado). Precision for d18O and dD was better than ±0.1 and ±0.4 per mil, respectively, based upon repeated measures of an internal standard (BW-1).  

BCO-DMO Processing:
- modified parameter names (replaced spaces with underscores);
- separated Dates_of_collection field into Date_Start and Date_End (yyyy-mm-dd).