Dataset: Measurements of the dissolved radium isotopes Radium-223, Radium-224, Radium-228 collected on the US GEOTRACES GP17-OCE cruise on R/V Roger Revelle (RR2214) in the South Pacific and Southern Oceans from December 2022 to January 2023

Because of their short half-life, Radium-223 and Radium-224 were measured onboard from large-volume samples via delayed coincidence counting (RaDeCC, Moore & Arnold, 1996), immediately after collection from the Mn-coated cartridges, and after rinsing with Ra-free water and drying to dampness. Radium-223, Radium-224, and Radium-228 were collected on manganese-coated cartridges filtered at depth using an adapted McLane in situ pump (WTS-LV). The pumps were programmed to filter 1500-2000 liters (L) of seawater per deployment. The cartridges were rinsed with radium-free fresh water, and excess moisture was removed using compressed air. In addition to the water column samples, large-volume surface samples were collected by pumping from a depth of 2 meters via a hand-deployable pump through 2 pre-filters, a single Mn-cartridge accompanied by a 15-25 liter sample that was passed through a 20 gram (g) Mn-fiber column to retain radium.

Radium-228 was measured via RaDeCC through Th-228 ingrowth. Cartridge efficiency was individually corrected from comparison between Ra-226 on cartridge and fiber samples. For select samples (DQ flag = C), Ra-228 was counted from the large volume samples via gamma spectroscopy for Ra-226, Ra-228, and Th-228 following the methods from Moore et al. (2024). The Mn cartridges were ashed in a muffle furnace at 820 degrees Celsius (˚C) for 48 hours, transferred to 15 or 25 millimeter (mm) diameter polystyrene vials and sealed with epoxy to prevent Rn-222 loss. After waiting at least three weeks for daughter isotopes to reach equilibrium, the samples were counted from 3-6 days in high purity, well-type germanium detectors at WHOI laboratories. Ra-226 activities were quantified via the Pb-214 photopeak at 352 keV and Ra-228 was quantified via the Ac-228 photopeaks at 338 and 911 keV.