Dataset: Dissolved radium isotopes for river and estuary samples collected from November 2022 to August 2023 along the West Florida Shelf

Surface water radium isotope samples were collected at all river and estuary stations via a submersible pump lowered ~1.0 m below the water’s surface. River samples were collected at upstream (60 L) and downstream (20 L) stations, and physicochemical parameters were recorded with a calibrated handheld water quality sonde (In Situ Aqua Troll 600). For estuary samples, the water column was characterized by a CTD cast (Seabird 19plus v2) and 20 L of water was collected for radium isotopes. For all sample types, dissolved radium samples were filtered at <1L/min onto a MnO₂-coated acrylic fiber to adsorb Ra. Samples were washed with Ra-free deionized water to remove salts and remaining particles, then dried to a 1:1 fiber:water mass ratio (Moore, 2008).

Short-lived ²²³Ra and ²²⁴Ra were measured using a delayed coincidence counter (RaDeCC) at Old Dominion University (Moore and Arnold 1996), following recommended best-practices (Diego-Feliu et al. 2020). Additional measurements were performed one month (²²⁸Th) and two months (²²⁷Ac) post-collection to assess parent activities supporting ²²³Ra and ²²⁴Ra. ²³²Th standards in equilibrium with ²²⁸Th were measured to assess detector efficiencies for ²²⁴Ra and ²²³Ra (Moore & Cai, 2013). Errors are propagated from counting statistics, chance-coincidence corrections, and detector efficiencies (Diego-Feliu et al. 2020). Following, the Mn-coated acrylic fibers were combusted at 850°C for 16 hours, homogenized, sealed with epoxy resin, and incubated for a minimum of three weeks until ²²²Rn was in secular equilibrium with its parent ²²⁶Ra. Long-lived Ra isotopes were measured via gamma spectroscopy in a Ge well-type detector for ²²⁶Ra (352 keV photopeak) and ²²⁸Ra (average of 338 and 911 keV photopeaks), with efficiencies calibrated using standards prepared in the same fashion as the estuarine samples (Charette et al., 2001). Select estuary samples were analyzed for ²²⁸Ra via ingrowth of ²²⁸Th using the RaDeCC system, following Moore (2008).