Water column samples were collected by Niskin bottle on a CTD rosette (\u201cCTD profile\u201d). NO3-+NO2- concentration was measured using a chemiluminescent method described by Braman and Hendrix, 1989, with a detection limit of 0.1 \u00b5M. NO3-+NO2- d15N and d18O analyses were by the \u201cdenitrifier method\u201d 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.
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The average precision of the nitrate+nitrite concentration measurement was <0.2 \u00b5M. The average precision of nitrate+nitrite d15N measurements was <0.2 per mil and for d18O was <0.3 per mil, but with the standard deviation for duplicate analyses of each sample reported here. NO3-+NO2- \u03b415N \u03b418O analyses were calibrated with IAEA N3 and USGS 34 NO3- d15N isotopic reference materials as described in McIlvin and Casciotti, 2011. NO3-+NO2- d18O were also calibrated with the USGS 35 isotopic reference material as described in McIlvin and Casciotti, 2011.
This data set includes water column nitrate+nitrite d15N and d18O measurements from the Gulf of Mexico and Florida Straits. These measurements were used to address whether Mississippi River nitrate is entrained in Loop Current waters and potentially exported from the Gulf of Mexico to the North Atlantic.\u00a0 Water samples were collected during R/V Pelican and R/V F.G. Walton Smith cruises in the Gulf of Mexico and Florida Straits between 2011 and 2018.
BCO-DMO Data Manager Processing Notes:
\n* converted xlsx file to csv
\n* latitude and longitude exported with 4 decimal places
\n* added a conventional header with dataset name, PI name, version date
\n* modified parameter names to conform with BCO-DMO naming conventions
\n* blank values in this dataset are displayed as \"nd\" for \"no data.\"\u00a0 nd is the default missing data identifier in the BCO-DMO system.
\n* Date format converted to ISO 8601 format yyyy-mm-dd
\n*\u00a0 Columns SigmaTheta,NO3_NO2,NO3_NO2_d15N, NO3_NO2_d18O, sal ,\u00a0temp rounded to two decimal places.