The expedition 64PE474 aboard RV Pelagia started on the 18th of July 2021, leaving from Reykjavik (Iceland), half a day later than initially planned owing to delayed luggage that also contained essential equipment for the expedition. The expedition ended on August 16th 2021, also in Reykjavik (Iceland). During the expedition, samples were taken using several systems. The ‘Titan’ ultraclean CTD sampling system (UCC) for trace metal collection (De Baar, et al. 2008), mounted with pristine large volume samplers (Rijkenberg, et al. 2015), was used the most as part of the trace metal focal point of the expedition. The large volume Pristine samplers were made from polypropylene to allow sampling for light sensitive phytoplankton. After deployment, the complete CTD sampling system was placed in a cleanroom environment inside a modified high cube shipping container where subsamples were collected for trace metals, isotopes, ligands, and various auxiliary parameters (see section 2.4). The other deployed instruments included a conventional CTD rosette system (CTD), a multi-corer (MUC) to collect sediment cores from which samples were taken for both sediments and porewaters, and a novel bottom gradient sampler (BGS) to sample dissolved and particulate trace metals close to the seafloor. Overall, 38 full depth stations were sampled with in total 38 UCC casts, 14 CTD casts, 19 BGS casts, and 13 MUC casts. Additionally, 2 shallow stations (station 4 and 26) were occupied to collect surface water to start the planned bioassays. During the expedition, 2 large, 6-day bio-assays were conducted (see section 2.5) to investigate the influence of Fe concentrations and temperature on phytoplankton biomass and composition. Another 2-day bioassay was also carried out to further investigate the influence of Fe and ammonium on phytoplankton productivity and composition. For these bioassays, 2 large custom-built temperature-controlled incubators where used that were place on the deck in front of the bridge of RV Pelagia where irradiance was mostly unobstructed. Additionally, 32 smaller bioassays were conducted by Willem Poll’s group at controlled temperature and irradiance levels inside a climate-controlled container laboratory on Pelagia. (2025-12-17)