Keywords: Alkalinity, total; Ammonium; Aphanizophyll; Aragonite saturation state; Baltic Sea; Bicarbonate ion; BIOACID; Biogenic silica; Biological Impacts of Ocean Acidification; Biomass/Abundance/Elemental composition; Calcite saturation state; Calculated; Calculated using seacarb after Nisumaa et al. (2010); Canthaxanthin; Carbon, inorganic, dissolved; Carbon, organic, dissolved; Carbon, total, particulate; Carbon/Nitrogen ratio; Carbon/Phosphorus ratio; Carbon/Silicon ratio; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Chlorophyll a; Chlorophyll b; Chlorophyll c2; Chlorophytes, biomass; Coast and continental shelf; Community composition and diversity; Cryptophytes, biomass; Cyanobacteria, biomass; DATE/TIME; Day of experiment; Diatoms, biomass; Dry mass; Entire community; Euglenophytes, biomass; Field experiment; Fluorescence determination; Fucoxanthin; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Hand-operated CTD (Sea&Sun Technology, CTD 60M); High Performance Liquid Chromatography (HPLC); KOSMOS_2012_Tvaerminne; MESO; Mesocosm experiment; Mesocosm label; Mesocosm or benthocosm; Myoxoxanthophyll; Neoxanthin; Nitrate and Nitrite; Nitrogen, organic, dissolved; Nitrogen, organic, particulate; Nitrogen/Phosphorus ratio; OA-ICC; Ocean Acidification International Coordination Centre; Other metabolic rates; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); Pelagos; pH; Phase; Phosphate; Phosphate, total, particulate; Phosphorus, inorganic, dissolved; Phosphorus, organic, dissolved; Prasinophytes, biomass; Prasinoxanthin; Salinity; Silicate; SOPRAN; Spectrophotometric; Surface Ocean Processes in the Anthropocene; Temperate; Temperature, water; Type; Violaxanthin