Dataset: Measurements of global dissolved submarine groundwater discharge (SGD) 226-Radium and 228-Radium

ValidatedFinal no updates expectedDOI: 10.26008/1912/bco-dmo.878519.1Version 1 (2022-08-16)Dataset Type:Other Field Results

Principal Investigator: Matthew A. Charette (Woods Hole Oceanographic Institution)

Co-Principal Investigator: Willard S. Moore (University of South Carolina)

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


Project: Collaborative Research: US GEOTRACES PMT: Sources and Rates of Trace Element and Isotope Cycling Derived from the Radium Quartet (PMT Radium Isotopes)


Abstract

This dataset includes measurements of global dissolved submarine groundwater discharge (SGD) 226-Radium and 228-Radium.

Samples were collected using either a peristaltic pump or a well pump and the groundwater was passed through a 1 or 5 μm prefilter to remove suspended sediment before being filtered at <1 L/min onto Mn-coated acrylic fiber. The fiber was rinsed with Ra-free MilliQ water to remove any salts or sediment, then partially dried.

Samples with low activities (<0.4 dpm) were analyzed for 228Ra via 228Th ingrowth using a delayed coincidence counter (RaDeCC) (Moore, 2008), as described in Charette et al. (2015). Briefly, when 228Ra is extracted onto the Mn fiber, 228Th is extracted in parallel. Using the initial concentration of 228Th and the concentration of 228Th after 1 to 2 years, measured via RaDeCC, along with the decay constants of 228Th and 228Ra, the initial concentration of 228Ra can be calculated. Low activity samples were analyzed for 226Ra via 222Rn emanation (Key et al. 1979), as described in Charette et al. (2015). Fibers were placed in a fiber holder that was then flushed with He for 5 minutes at 250 mL/min, sealed, and left for two weeks before analysis via 222Rn ingrowth and scintillation counting. These two methods were used for low activity samples due to better method sensitivity than gamma counting (Charette et al., 2001), which was used for samples with high activities (>0.4 dpm per sample). For this method, the fibers were ashed (880 °C, 16 h), homogenized, capped with epoxy resin, and left for >3 weeks to obtain secular equilibrium between 226Ra and its daughter radionuclides. The samples were then counted in a well-type gamma spectrometer for 228Ra (via 228Ac at 338 keV) and 226Ra (via 214Pb at 351.9 keV) (Charette et al., 2001).

When not specifically listed, errors are 10%.


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Related Publications

Methods

Charette, M. A., Buesseler, K. O., & Andrews, J. E. (2001). Utility of radium isotopes for evaluating the input and transport of groundwater-derived nitrogen to a Cape Cod estuary. Limnology and Oceanography, 46(2), 465–470. Portico. https://doi.org/10.4319/lo.2001.46.2.0465
Methods

Charette, M. A., Morris, P. J., Henderson, P. B., & Moore, W. S. (2015). Radium isotope distributions during the US GEOTRACES North Atlantic cruises. Marine Chemistry, 177, 184–195. doi:10.1016/j.marchem.2015.01.001
Methods

Key, R. M., Brewer, R. L., Stockwell, J. H., Guinasso, N. L., & Schink, D. R. (1979). Some improved techniques for measuring radon and radium in marine sediments and in seawater. Marine Chemistry, 7(3), 251–264. doi:10.1016/0304-4203(79)90042-2
Methods

Moore, W. S. (2008). Fifteen years experience in measuring 224Ra and 223Ra by delayed-coincidence counting. Marine Chemistry, 109(3-4), 188–197. doi:10.1016/j.marchem.2007.06.015