Seawater carbonate chemistry and carbon fixation of a temperate plankton community in response to calcium- and silicate-based Ocean Alkalinity Enhancement

A Large-scale mesocosm experiment was conducted in the temperate fjord ecosystem near Bergen, Norway during late spring 2022 to investigate the effects of OAE on biogeochemical processes and organisms under close-to-natural conditions. A non-CO2-equilibrated approach was chosen, simulating OAE with calcium- and silicon-based minerals. A gradient of five OAE levels was achieved by increasing total alkalinity (TA) by 0–600 µmol kg-1. Carbonate chemistry parameters were monitored for the total length of the 53-day experiment. The added TA remained relatively stable over the experimental period and the measured CO2 gas exchange rate was comparable to what would be expected for large oceanic regions. The study and data set offer insights into impacts of non-equilibrated alkalinity enhancement on the carbonate system, air-sea gas exchange and carbon fixation.