The CO2MARINE sets out to assess the impact of increased CO2 level on geochemical processes in marine sediments and sea water as well as on benthic biota at relevant hydrostatic pressure. The project proposal addresses environmental risk assessment related to potential CO2 leakage from sub-seabed storage reservoir as described in thematic area “Environmental impact” of the CCS 2013 call and, more generally, is in line with the EU strategy on reduction of CO2 emission. In a series of laboratory experiments, surface sediments and benthic species from the potential CO2 storage site in the Polish part of the southern Baltic Sea will be exposed to different CO2 levels at high water pressure thus imitating closely natural environmental conditions at the seafloor. Access to cutting-edge experimental facility (the hyperbaric TiTank) will allow us to study CO2-induced modifications to chemical gradients across sediments and mobilization processes of trace elements, heavy metals and organic pollutants, and their combined effects on marine organisms. Biological impacts will be measured at different levels of biological organization, going from gene, cell and tissue to individual, species and community, and functions including behaviour, physiological and enzymatic activity. The CO2MARINE will generate novel empirical data from high-pressure experiments and unique direct observations covering a range of potential CO2 exposure levels, operating over short periods of time, to define early-warning chemical indicators and biomarkers of environmental stress due to CO2 leak. The ultimate aim of the proposal will be to identify appropriate chemical and biological methods to monitor the marine environment above a storage site, thereby providing support to potential CO2-storage operators and environmental management of CCS under seabed in the Baltic Sea.