The aim of the research cruise 64PE460 to the North Sea for Mareike Paul's PhD project was to investigate trace metal sequestration and mobilization in North Sea sediments. Due to their redox-sensitive behaviour, sedimentary trace metals serve as potential proxies for past oxygen conditions in coastal areas.
The focus of this cruise was on the muddy locations like the German Bight, as most of the targeted trace metal dynamics were expected to happen there. But as the North Sea is a very dynamic system strongly influenced by tidal cyclicity and lateral transport, silty and sandy locations were included in this research cruise proving the possibility to reveal yet undiscovered trace metal signals and fluxes in non- or less muddy sediments.
In total 6 stations were sampled: 1. Frysian Front, 2. Oyster Grounds, 3. Dogger Bank, 4. Devil's Hole, 5. South of Fisher Bank and 6. German Bight.
At each station, 5 multiple sediment cores (MUC cores) were taken for different purposes. Two cores were frozen for storage, one core was sampled under oxic condition for dating and porosity analyses, one core was used for resin embedding and the last one for sampling under anoxic conditions to prevent post-oxidation and mobility of certain trace metals. As not all stations were suitible for taking MUC cores, a special tube with holes was used for sampling for porewaters as a back up. The samples from the anoxic core were further subsampled for nutrients (N, P, Si), H2S, organic matter (e.g. DIC), alkalinity and metals. Both sampling and subsampling was done in a N2 flushed glove bag.
Additionally to Mareike's own project, she was also responsible for collecting water column samples from CTD casts for a colleague. Those samples were further processed on board for later analysis of alkalinity, DIC and metal contents in a similar way as the anoxic core subsampling.
Right from the start, working onboard the Pelagia was quite challenging as the crew and scientific team ran into several technical issues as well experiencing very rough weather. For the first time, Mareike was leading a small team of two Master students from Utrecht University. That was a new experience for her as well but in the end the small group worked well in a team and they overcame all of the above problems and challenges.
The 64PE460 research cruise was led by Karline Soetaert from NIOZ (Yerseke, The Netherlands) and remotely by Peter Kraal from NIOZ (Texel, The Netherlands). The participation of Mareike Paul was part of the research project “Sedimentary trace metals: unlocking the archives of coastal marine hypoxia” funded by the Academy of Finland (Research Fellowship to Tom Jilbert) in collaboration with Caroline Slomp's working group at Utrecht University, where many samples are going to be analyzed in 2020.