Dataset: Radium isotope (223Ra, 224Ra, and 226Ra) measurements from CTD and underway water samples collected on R/V Endeavor cruise EN640 from June-July 2019

Water samples for radium isotope analysis were collected from both the ship's clean underway intake system ('U' designator in data) and niskin bottles attached to the CTD rosette ('C' designator in data). Salinity data were derived from the ship's clean underway intake system with SBE 21 SEACAT Thermosaliograph. Water samples were filtered through 47 mm GFF filters (unless otherwise noted), then passed slowly through 25 g (dry) acrylic fibers impregnated with MnO2 (Moore, 1976). Fibers were then washed 10x with Ra-free freshwater to remove salts and dried to a mass between 35 and 57 g for optimal humidity levels (Sun and Torgersen, 1998). Fibers were then immediately counted on a Radium Delayed Coincidence Counter (RaDeCC; Moore and Arnold, 1996) for total Ra-224 and Ra-223. Roughly 3 weeks later, fibers were counted again for supported Ra-224. Thus, excess ('XS') Ra-224 is the difference between total and supported Ra-224 measurements. Ra-226 activities were then measured on a radon emanation line as per Peterson et al. (2009).

Minimum detectable activities (dpm/100L) are calculated based on Currie (1968). Any measured values lower than the minimum detectable activity is labeled 'BD' in the dataset.