This dataset is from an experiment with large-volume in situ mesocosms (~55-60 m3 and 21 m depth) in Raunefjord (Bergen), Norway in 2015. In this pelagic in situ mesocosm experiment, we assessed how ocean acidification (particularly episodic extreme events) affect natural plankton communities. A particular focus was the response of the appendicularian Oikopleura dioica, and its influence on vertical carbon fluxes. Therefore, we sampled ecological and biogeochemical key parameters for 49 days in regular intervals.