Dataset: Nutrient and nitrate isotope data from the southern Benguela upwelling system from February to August 2017

Final no updates expectedDOI: 10.26008/1912/bco-dmo.811839.1Version 1 (2020-05-19)Dataset Type:Cruise Results

Principal Investigator: Julie Granger (University of Connecticut)

Principal Investigator: Samantha Siedlecki (University of Connecticut)

Contact: Raquel Flynn (University of Cape Town)

BCO-DMO Data Manager: Mathew Biddle (Woods Hole Oceanographic Institution)


Project: Investigation of mechanisms leading to seasonal hypoxia in the Southern Benguela Upwelling System (SBUS Hypoxia)


Abstract

Analysed Particulate Organic Matter data, Nutrient data and Nitrate isotope data from the 2017 Integrated Ecosystem Programme: Southern Benguela (IEP:SB) cruises conducted in February, May, and August 2017. The IEP:SB is a multi-disciplinary, multi-institutional platform to undertake relevant science in the Southern Benguela; also functioning as a platform for collaboration and learning. Nitrate+nitrite concentrations were measured on a Lachat QuickChem flow injection analysis platform in a ...

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CTD data:
The temperature and conductivity probes are calibrated annually by the manufacturer while the oxygen sensor was calibrated against discrete seawater samples analyzed for dissolved oxygen concentrations by Winkler titration (Carpenter 1965; Grasshoff et al. 1983).

Nutrients:
Duplicate samples were measured for nitrate+nitrite on different days, and the standard deviation for duplicates was <0.5 µM, with a lower standard deviation for lower concentration samples
Duplicate samples for phosphate and nitrite were measured in duplicate on different days of analysis, yielding a standard deviation for duplicates of ≤0.1 µM. 

Nitrate isotopes:
The N and O isotope ratios of nitrate were measured in triplicate in separate batch analyses and standard deviations for both δ15N and δ18O were <0.3‰. Certified nitrate isotope ratio reference materials in nutrient-free seawater were measured in all batch analyses. These included IAEA-NO3-, with δ15N of 4.7 ± 0.2‰ vs. N2 air (Gonfiantini et al. 1995) and and δ18O of 25.6 ± 0.4‰ vs. VSMOW (Böhlke et al. 2003), and USGS-34, with δ15N of -1.8 ± 0.1‰ vs. N2 air and δ18O of -27.9 ± 0.3‰ vs. VSMOW (Böhlke et al. 2003). Nitrate isotstandards in individual runs were diluted in nutrient-free seawater to concentrations similar to those of the samples to account for potential matrix effects on the δ18O measurements (Weigand et al. 2016). Reproducibility was monitored by analysis of an internal seawater nitrate standard from the deep North Atlantic.


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Methods

Bendschneider, K., and Robinson, R.J. (1952). A new spectrophotometric method for the determination of nitrite in sea water. Technical Report No. 8. University of Washington
Methods

Böhlke, J. K., Mroczkowski, S. J., & Coplen, T. B. (2003). Oxygen isotopes in nitrate: new reference materials for18O:17O:16O measurements and observations on nitrate-water equilibration. Rapid Communications in Mass Spectrometry, 17(16), 1835–1846. doi:10.1002/rcm.1123
Methods

CARPENTER, J. H. (1965). THE CHESAPEAKE BAY INSTITUTE TECHNIQUE FOR THE WINKLER DISSOLVED OXYGEN METHOD. Limnology and Oceanography, 10(1), 141–143. doi:10.4319/lo.1965.10.1.0141
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

Diamond, D. (1994). QuikChem Method 10-114-21-1-B: Silicate by flow injection analysis. Lachat Instruments