To investigate the influence of organic matter (OM) on rare earth element (REE) distributions and patterns in the marine environment we monitored concentrations of dissolved REEs (dREEs) during an artificially induced spring bloom. Our mesocosm approach mimicked a neritic North Sea water body. Three biological replicates (P2-P4) were inoculated with a phytoplankton and associated bacterial community, which was retrieved in March 2018 from the southern North Sea. The incubation was monitored for 38 days. The experiment additionally covered the investigation of two biota-free controls. A variety of parameters were sampled, the results of some can be found in Mori et al. (2021; doi:10.1016/j.gca.2021.08.002).Samples for dREE analyses were taken at intervals of 1-5 days. Preconcentration, analysis and quantification of dREEs followed the method described in Behrens et al. (2016; doi:10.1016/j.marchem.2016.08.006.). Concentrations were normalized to the Post Archaen Australian Shale (Rudnick and Gao, 2003). We further normalized concentrations throughout the experiment to initial concentrations (T0-normalization) and calculated loss and gains of dREEs.