Impact on bacterial activities of ocean sequestration of carbon dioxide into bathypelagic layers

The ocean sequestration of carbon dioxide (CO 2 ), direct injection of CO 2 into bathypelagic layers, is one of the climate change mitigation options. It is essential to assess the potential environmental impacts on the marine ecosystem. In bathypelagic layers, bacteria are dominant organisms and play significant roles in oceanic carbon cycling through utilization and transformation of organic matter. We performed laboratory experiments by acidifying bathypelagic seawater with CO 2 gas or buffer solutions to examine the impact on bacterial activities (abundance, production rate, and proportion of viable cells). In the laboratory experiments, we observed some potential effects by artificial changes in CO 2 concentration, pH, or both, on bacterial activities. It was suggested that trophic conditions of bacterial assemblage strongly influence the magnitude of the impacts on bacterial activities and metabolisms by CO 2 sequestration.