Dataset: Water column Th-234 activities
Deployment: DY077

Samples were collected during two deployment cycles (termed “deployment 1” and “deployment 2”) occupied during the RRS Discovery cruise DY077 to the Porcupine Abyssal Plain Sustained Observatory (PAP-SO) Site in April 2017. In each of the cycles, we conducted particle flux sampling method intercomparisons between fluxes derived from upper water column deficits of 234Th vs. its parent isotope 238U, two types of neutrally buoyant sediment traps (NBST and PELAGRA), and a surface tethered array of sediment traps (STT).
234Th profiles were sampled at the beginning and end of each deployment, triangulated 10 km apart around the drifting trap location (Figure 1). A total of 161 234Th samples were collected (Table 1). A 4-L sample was collected from CTD casts, a stable Th yield monitor was added and the pH was adjusted to promote the formation of a Mn precipitate that scavenges Th. This was then filtered onto a 25-mm diameter quartz filter (Buesseler et al., 2009). The quartz filter was dried and mounted, then beta counted on board and again 6 months post-cruise to determine the amount of interfering beta activity and detector background that was not associated with 234Th in the sample.

Porcupine Abyssal Plain Sustained Observatory (PAP-SO) site in the Northeast Atlantic Ocean (49°N, 16.5°W)