Particulate Thorium-234 activity along the equatorial Atlantic collected on RV METEOR during cruise M181 Cape Town - Mindelo, 2022-04-17 - 2022-05-27

This dataset includes 234Th activity (dpm/L) measured in particulate samples across small (1-51 µm) and large (>51) size friction, which were sampled as a part of the TRATLEQ-II from April 17th to May 28, 2022, onboard the R/V Meteor (M181). During M181, 6 large volume insitu pumps (4 from McLane Research Laboratories and 2 from Challenger Oceanic) to sample 2 size classes of particles at 6 depths at a time. Sampling depths between the surface and 500 m were chosen such that the resulting profiles represent as well as possible the depth variability of the POC/234Th ratio. 4 pumps were deployed in the productive surface layer down to 150 m and 2 pumps below this depth. We obtained 10 pump profiles evenly distributed every 5° longitude between 1° East and 44° West. Each pump was equipped with two filters in sequence, a first prefilter made of Nitex tissue with a mesh size of 50µm to sample the large size settling particles, and a micro quartz filter (QMA, 1 μm nominal size) of 142 mm (McLane) and 293 mm (Challenger) diameter to sample the suspended small particles. The large particles collected on the prefilter were rinsed off with filtered (0.2 µm) seawater and filtered on a 25 mm QMA filter, and the small particles from the QMA filters were subsampled by punches, one on the 142 mm and 18 punches on the 293 mm filters. Punches and rinsed particles were mounted on sample holders for beta counting as was done for the 234Th precipitate. The International GEOTRACES protocol was followed for both sampling and analysis for particulate samples as explained in Bam et al. 2023 and Clevenger et al., 2024.