Planktic foraminifer shells were picked from Oceanic Flux Program (OFP) sediment traps at 500 m, 1500 m, and 3200 m water depth (Conte et al., 2001; Conte and Weber, 2014). After crushing and the appropriate cleaning steps (Ren et al., 2012; Ren et al., 2015), shell-bound N was released by dissolution with hydrochloric acid, and organic N converted to nitrate using a basic persulfate oxidising reagent (POR; a potassium persulfate/sodium hydroxide solution) (Nydahl, 1978; Knapp et al., 2005). The \"denitrifier method\"\u00a0was used to convert sample nitrate to N2O gas for isotope analysis (Sigman et al., 2001; Casciotti et al., 2002; Weigand et al., 2016). See methods section of Smart et al. (2018) for more details of sample collection, isotope analysis and data quality.
\nThe isotopic composition of N2O was measured at Princeton University by GC-IRMS using a Thermo MAT 253 mass spectrometer with a purpose-built on-line N2O extraction and purification system. See methods section of Smart et al. (2018) for more details of sample collection, isotope analysis and data quality.
Planktic foraminifer shell d15N from sediment traps in the Sargasso Sea (off Bermuda) in the western subtropical North Atlantic.\u00a0Sediment traps from 500 m, 1500 m, and 3200 m water depth (31\u00b050\u2019N, 64\u00b010\u2019W).
\nData published in:
\nSmart, S.M., H. Ren, S.E. Fawcett, R. Schiebel, M. Conte, P.A. Rafter, K.K. Ellis, M.A. Weigand, S. Oleynik, G.H. Haug, D.M. Sigman (2018). Ground-truthing the planktic foraminifer-bound nitrogen isotope paleo-proxy in the Sargasso Sea, Geochimica et Cosmochimica Acta, doi:\u00a0https://doi.org/10.1016/j.gca.2018.05.023
Data Processing:\u00a0Isotope ratio measurements were referenced against automated injections of N2O from a gas cylinder, and then calibrated to N2 in air using two international reference materials IAEA-N3 and USGS-34 that were included in every run. An in-house N2O standard was also measured along with each batch of samples to monitor mass spectrometry. Oxidized samples were additionally corrected for the contribution of the N blank associated with the POR.
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