TPC, PIC, POC, TPN, and Th-234 from in-situ pumps at the Porcupine Abyssal Plain Sustained Observatory (PAP-SO) site in the Northeast Atlantic Ocean during RRS Discovery cruise DY077 in April of 2017 (NCEI Accession 0278573)

Acquisition Description:
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 (Figure 1). 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). DY077 samples analyzed in US (WHOI and Skidmore College) are archived here; DY077 samples analyzed in the UK (NOC) are archived in the British Oceanographic Data Centre. Two McLane in-situ battery powered pumps were deployed two times for the collection of size fractionated particles. The water passes first through a 51-micron screen followed by a nominal 1-micron quartz filter. Filter diameters are both 142 mm and a baffled opening developed for the GEOTRACES program keeps particles from washing off the top screen during retrieval of the pumps as they ascend on the wire. The pumps were programmed with a 1-hour delay time before turning on at depths of 200 and 350 m. After a pumping time of 2 hours, the pumps shut off and were retrieved. After retrieval, volumes were noted (measured by dual flow meters), any water that remained in the pump was drained through the filters, and the screen was rinsed with prefiltered seawater onto a 1-µm pore size silver filter (25-mm diameter).

The Ag filter and a 25-mm subsample from the QMA were dried at 45°C, mounted, and immediately counted for low-level β emission onboard the ship. At WHOI, a subset of samples was re-counted approximately one month later on shore. Final background counts to measure non-234Th related β emissions were conducted approximately six months later. At this point, filters were unmounted, re-dried, and gravimetrically subdivided into four sections. One half of the filter was analyzed for total carbon and nitrogen after high-temperature combustion on a Thermo Electron FlashEA 1112 C/N analyzer. Coulometric analysis for PIC after sample acidification was performed on a quarter of the filter (Johnson et al, 1985; Honjo et al, 2000). The remainder of the filter was archived.

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