Dataset: Nitrate N and O isotopes from the GP12 ("PANDORA") cruise in the South-West Pacific and Solomon Sea from June to August 2012 carried out as part of the international GEOTRACES program

ValidatedFinal no updates expectedDOI: 10.26008/1912/bco-dmo.838914.1Version 1 (2021-01-27)Dataset Type:Cruise Results

Principal Investigator: Patrick Rafter (Princeton University)

Co-Principal Investigator: Catherine Jeandel (Laboratoire d’Etudes en Géophysique et Océanographie Spatiales)

Co-Principal Investigator: Daniel M. Sigman (Princeton University)

BCO-DMO Data Manager: Shannon Rauch (Woods Hole Oceanographic Institution)


Program: U.S. GEOTRACES (U.S. GEOTRACES)

Project: Understanding the nitrogen isotopes of planktonic foraminifera: A modern Sargasso Sea study (N Isotopes Foraminifera)

Project: Collaborative Research: US GEOTRACES PMT: Investigating geochemical tracers of the Pacific nitrogen cycle and budget (PMT Nitrate)

Project: Collaborative Research: GEOTRACES Atlantic Section Nitrate Isotope Measurements (GP12) (GT Atlantic Nitrate)


Abstract

Nitrate N and O isotopes from the GP12 ("PANDORA") cruise in the South-West Pacific and Solomon Sea from June to August 2012 carried out as part of the international GEOTRACES program. This dataset was supported by NSF OCE-1060947, NSF OCE-1736652, NSF OCE-0960802, and the Grand Challenges Program of Princeton University.

Briefly, samples were acquired and kept frozen until analysis using the Denitrifier Method (Sigman et al. 2001; Casciotti et al. 2002) at Princeton University.

The following methods are further described in the Intercalibration Report (PDF) for this dataset (also provided under Supplemental Files).

Sampling and storage procedures followed the GEOTRACES cookbook: (1) seawater samples were collected from Niskin bottles into pre-rinsed square 60 mL high-density polyethylene (HDPE) bottles, (2) Each sample was filled to approximately ¾ the bottle height to prevent sample overflow during ice expansion, (3) Samples were stored immediately in upright position at -20°C. The one difference between the sampling for the PANDORA cruise and the GEOTRACES cookbook is that these samples were not filtered before freezing. As per the GEOTRACES cookbook, filtration is recommended, but prior tests showed no difference between filtered and non-filtered samples for nitrate isotope measurements (at least within 18 months of sampling).

Samples were analyzed by the Denitrifier Method (Casciotti et al., 2002; Sigman et al., 2001), with technical updates described by (Weigand et al., 2016). Specific protocols for these samples are described in (Marconi et al., 2015) and in detail along with extensive analysis of reference solution results in Weigand et al., 2016. All isotope analyses were performed on a MAT253 Thermo IRMS equipped with a custom-sample preparation system, described by Weigand et al. (2016). Nitrite was not removed from these samples, so they should be considered as possibly "Nitrate + Nitrite" measurements. 

Raw data were calibrated to nitrate reference materials IAEA-NO3 and UGSS34, dissolved in low-nitrate seawater collected from the mixed layer at BATS. Samples were bracketed in nitrate concentration by the reference nitrate solutions. When nitrate reference solutions indicated a concentration trend in nitrate d18O, a correction was applied based on those results. These and other aspects of the data processing are described in detail by Weigand et al. (2016).


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Related Publications

Methods

Casciotti, K. L., Sigman, D. M., Hastings, M. G., Böhlke, J. K., & Hilkert, A. (2002). Measurement of the Oxygen Isotopic Composition of Nitrate in Seawater and Freshwater Using the Denitrifier Method. Analytical Chemistry, 74(19), 4905–4912. doi:10.1021/ac020113w
Methods

Sigman, D. M., Casciotti, K. L., Andreani, M., Barford, C., Galanter, M., & Böhlke, J. K. (2001). A Bacterial Method for the Nitrogen Isotopic Analysis of Nitrate in Seawater and Freshwater. Analytical Chemistry, 73(17), 4145–4153. doi:10.1021/ac010088e
Methods

Weigand, M. A., Foriel, J., Barnett, B., Oleynik, S., & Sigman, D. M. (2016). Updates to instrumentation and protocols for isotopic analysis of nitrate by the denitrifier method. Rapid Communications in Mass Spectrometry, 30(12), 1365–1383. doi:10.1002/rcm.7570