To investigate links between biological, biogeochemical and physical parameters, we closely monitored 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).Total alkalinity was sampled daily. For the analysis we used a multiscan GO microplate spectrophotometer (Thermo Scientific) and followed the method described by Sarazin et al. (1999; doi:10.1016/S0043-1354(98)00168-7).