Potential effect of CO2 seepage at high pressure on the marine organic matter

Seepage from a carbon capture and storage site (CCS) under the seabed can lead to CO2 enrichment of the surrounding seawater. This seepage may cause changes that alter the composition of the marine dissolved organic matter (DOM) pool. This study evaluated possible changes in the composition of the DOM in the event of CO2 seepage in sediments from a CCS site in the Baltic Sea. High-pressure (9 atm) and low pH (pH 7) conditions were simulated using a hyperbaric titanium tank over a period of 40 days. The DOM composition was analyzed by liquid chromatography coupled to a high-resolution mass spectrometer (LC-HRMS) with electrospray (ESI) as ionization mode in both positive and negative polarities. An effect of the pH7 conditions on the DOM compounds was detected in both ionization modes. In this study, it was possible to determine whether the changes observed on the DOM were caused by natural seawater variation or by the effect of pH 7. Results showed that the composition of organic compounds can be impacted in seepage areas where a pH 7 occurs.