Dataset: Guaymas Sedimentary Radium AT37-06
Deployment: AT37-06

Samples for this dataset were collected as push cores using the HOV Alvin submersible. Analytical methods for measuring particulate Ra-224 and Th-228 are based on methods described in Cai et al. (2012; 2014). In short, once the cores were recovered on the ship, overlying waters were siphoned off and the sediment cores were sectioned in 2 cm vertical intervals for the top 10 cm, then 4 cm intervals for the remainder of the core. A slurry was prepared by adding ~¼ of the sediment volume (or ~1/8 of the sediment volume for the 4 cm intervals) to 150 mL of Ra-free tap water. The pH of the slurry was adjusted by adding 5-10 drops of concentrated NH3-OH, after which 1 mL of 19 mM KMnO4 and 1 mL of 40 mM MnCl2 solutions were added to precipitate any dissolved radium and thorium. A portion of this slurry was vacuum-filtered onto pre-weighed 47 mm diameter GFF filters until no further drops passed through the filter. Filters were dried in a drying oven (at 60 °C) for 12 hours, then placed is a filter holder within a cartridge and counted on a Radium Delayed Coincidence Counter (Moore and Arnold, 1996). Results from this analysis represent particulate Ra-224 activities. Filters were then measured on the Radium Delayed Coincidence Counter again after 3 weeks, from which the results are representative of Th-228 activities on the sediments.