Dissolved thorium-230 and thorium-232 from R/V Pelican cruise PE17-24 in the deep Northern Gulf of Mexico during June 2017 (NCEI Accession 0277720)

Acquisition Description:
Sampling occurred according the GEOTRACES cookbook recommendations for radionuclides ( https://www.geotraces.org/methods-cookbook/ ). Water was filtered from standard Niskin bottles through a 0.45 micron Acropak capsule filter and teflon line tygon tubing. Water was acidified to 0.024 M HCl using optima acid once the samples were returned to the lab about 2-3 days after collection. Water samples were left to sit acidified for at least 3 months prior to analysis to avoid adsorption loss.

Analysis of the thorium isotopes was by isotope dilution inductively-coupled plasma mass spectrometry as described by Hayes et al. (2017). Briefly, thorium-229 was added to acidified 4-liter water samples and allowed to equilibrate overnight. About 10 mg of Fe from an iron chloride solution was added and pH was raised with optima ammonium hydroxide to 8-9 and iron (oxy)hydroxide precipitate was allowed to settle for 2 days. Overlaying seawater was decanted and the iron precipitate was isolated using a series of centrifugation steps. The precipitate was digested with HNO3, HF and H2O2, then thorium was purified using anion exchange resin AG1-X8. Final solutions were dried down and taken up in 2% HNO3 for analysis on ICP-MS.