Dataset: Nitrate + nitrite isotope measurements from surface and water-column profiles in the Atlantic Sector of the Southern Ocean during the SCALE 2019 cruise aboard the S.A. Agulhas II from Oct 2019 to Nov 2019

Surface and water-column profiles were sampled aboard S/A Agulhas II in the late spring/early summer Atlantic Sector of the Southern Ocean, starting and ending in Cape Town, South Africa along the Good Hope line to the ice edge, from October 2019 to November 2019. Water column samples were collected by Niskin bottle on a CTD rosette (“CTD profile”). 

NO3-+NO2- d15N and d18O

The isotopic composition of NO3-+NO2- was determined 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, 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 and d18O of samples was calibrated with the international isotopic reference materials as described above.