Abstract To evaluate chronic impacts of CO 2 ocean sequestration, we simulated the distribution of injected CO 2 using an oceanic general circulation model (OGCM) with a horizontal resolution of 0.1°. The model can explicitly express transport and dispersion of dissolved CO 2 by mesoscale eddies. The CO 2 which is continuously injected by a moving ship dissolves and accumulates within the first several to 10 years, but the CO 2 concentration has an upper limit after its initial increase as a result of the dilution effect of mesoscale eddies which counterbalances the accumulation effect of injection. We can estimate the CO 2 injection flux with the CO 2 maximum concentration below the “Predicted No Effect Concentration” (PNEC), an index to estimate concentration causing no effects on biota.