Radium and thorium isotopes measured in the Western Arctic as part of the 2015 US GEOTRACES Arctic Cruise on the USCGC Healy (HLY1502) from August to October 2015 (NCEI Accession 0291583)

Acquisition Description:
Water column sampling:
Radium and thorium isotopes were collected on manganese-coated cartridges filtered at depth using an adapted McLane in situ pump (WTS-LV). The pumps were programmed to filter 1500-2000L of seawater per deployment. Water (15-25 L) was also collected at the same depth using a 30L Niskin bottle; these samples were filtered (at <1L/min) through a manganese-coated acrylic fiber and used to calculate radium extraction efficiency of the pumped samples. The cartridges were rinsed with radium-free fresh water and excess moisture was removed using compressed air. Samples were analyzed three times using a delayed coincidence counter (RaDeCC) for 223Ra, 224Ra, 228Th, and 227Ac. The cartridge and fiber media were ashed at 820 degrees C and measured on gamma detectors for long lived radium (226Ra, 228Ra) and thorium isotopes. 226Ra was determined via alpha scintillation counting of the Niskin bottle Mn fiber samples.

Surface water sampling:
Surface water radium samples (280 L) were collected from approximately 2 m using a submersible surface pump and filtered through a manganese coated acrylic fiber, which quantitatively scavenges radium from the seawater. Fiber samples were then ashed in a muffle furnace at 820 degrees C for 24 hours and the fiber ash was transferred to polystyrene vials, sealed with epoxy (to prevent 222Rn loss), and counted on high purity, well-type germanium detectors to measure 228Ra, using the lines of 228Ac (338 KeV and 911 KeV), and 226Ra, using the line for 214Pb (352 KeV). Detector efficiencies were determined by measuring ashed fiber standards prepared with a standard solution containing 226Ra and 232Th with daughters in equilibrium.