The overall objective of our project is to determine the importance of greenhouse gases, as well as mercury, for chemical and biological exchange processes in the marine environment with focus on polar regions and their feedback mechanisms in the context of a changing climate. Within this context a first in a series of laboratory (and field) experiments was designed to study interaction effects of increased temperature and increased carbon dioxide on a sea-ice-inhabiting diatom. CO₂ treatments were 380 ppm (present day) and 970 ppm (projected year 2100). Temperatures were ambient and +4°C. Biological variables measured were photosynthetic activity, growth and photosynthetic pigments. The CO₂ system was described by measuring total alkalinity (AT), pH, temperature and salinity: from these variables for example fugacity of CO₂, DIC, [CO₂], [CO₃^2–] and [HCO₃^–] was calculated. Results are currently analysed and will be presented on the poster.