ABSTRACT

For the assessment of the long-term consequences of the carbon dioxide ocean sequestration, the CO₂ injection into the middle depth parts of the ocean was simulated using a geochemical box model of the global carbon cycle. The model consists of 19 reservoir boxes and includes all the essential processes in the global biogeochemical cycles, such as the ocean thermohaline circulation, the solubility pump, the biological pump, the alkalinity pump and the terrestrial ecosystem responses. The present study aims to reveal the effectiveness and consequences of the direct ocean CO₂ sequestration in relation to both lowering the atmospheric transient PCO₂ peak and reduction in future CO₂ uptake potential of the ocean. We should note that the direct ocean injection of CO₂ at the present time means the acceleration of the pH lowering in the middle ocean due to the eventual and inevitable increase of CO₂ in the atmosphere, if the same amount of CO₂ is added into the atmosphere-ocean system. The minimization of impact to the whole marine ecosystem might be attainable by the direct ocean CO₂ sequestration through suppressing a decrease in the pH of the surface ocean rich in biota. The geochemical implication of the ocean sequestration is such that the maximum CO₂ amount to invade into the ocean, i.e., the oceanic CO₂ uptake potential integrated with time until the end of fossil fuel era, is only dependent on the atmospheric PCO₂ value in the ultimate steady state, whether or not the CO₂ is purposefully injected into the ocean; we gave the total potential capacity of the ocean for the CO₂ sequestration is about 1600 GtC in the case of atmospheric steady state value (PCO₂) of 550 ppmv.