Nitrate plus nitrite isotopic compositions from Leg 1 of the Antarctic Circumnavigation Expedition (ACE) research cruise onboard the R/V Akademik Treshnikov from December 2016 to January 2017 (NCEI Accession 0294398)

This dataset contains chemical and physical data collected on R/V Akademik Tryoshnikov during cruise ACE_Leg1 in the Indian Ocean from 2016-12-26 to 2017-01-17. These data include d15N, density, depth, and oxygen 16 to oxygen 18 ratio. The instruments used to collect these data include Isotope-ratio Mass Spectrometer and Niskin bottle. These data were collected by Angela N. Knapp of Florida State University and Sarah E. Fawcett of University of Cape Town as part of the "Collaborative Research: Quantifying the effects of variable light and iron on the nitrate assimilation isotope effect of phytoplankton (Nitrate Assimilation Phytoplankton)" project. The Biological and Chemical Oceanography Data Management Office (BCO-DMO) submitted these data to NCEI on 2023-07-24.

The following is the text of the dataset description provided by BCO-DMO:

ACE-Leg 1 NO3 Isotopes

Dataset Description:
Methods and Sampling:
Samples were collected during Leg 1 of the Antarctic Circumnavigation Expedition (ACE) research cruise onboard the R/V Akademik Treshnikov, which took place in the Indian Sector of the Southern Ocean from December 2016 to January 2017. Water column samples were collected by Niskin bottle on a CTD rosette. Surface samples were collected from the ship's underway intake (at ~5 meters depth). Nitrate and nitrite (NO3- + NO2-) d15N and d18O analyses were 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 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 nanomoles (nmols) N2O, which was then purged from the vial using a helium carrier gas. The d15N and d18O of samples were calibrated with the international isotopic reference materials as described below.

The average precision of nitrate+nitrite d15N measurements was <0.2 per mil and for d18O was <0.3 per mil. NO3-+NO2- d15N and d18O analyses were calibrated with IAEA N3 and USGS 34 NO3- d15N isotopic reference materials as described in McIlvin and Casciotti (2011). NO3-+NO2- d18O was also calibrated with the USGS 35 isotopic reference material as described in McIlvin and Casciotti (2011).