IPCC AR4 reported that the emission of the anthropogenic Carbon Dioxide (CO2) increase the CO2 concentration in atmosphere after the Industrial Revolution, and increasing of CO2 concentration caused the global warming. Moreover, it is shown that CO2 dissolution into the ocean causes the acidification in the surface layer. The buffering effect of the ocean can suppress the change of the CO2 concentration in the atmosphere. However, the rise of the CO2 concentration in the ocean surface means the pH of seawater decreases. This phenomenon continues until the difference of CO2 partial pressure between the atmosphere and the ocean disappears if the emission of CO2 is stopped. But, the acidification of the ocean progresses as long as it keeps CO2 emission. It is feared that the ocean acidification has crises influence on various organisms and entire ocean ecosystem. Carbon Capture and Storage is one of the mitigation measure technologies of CO2 emission. Famous carbon storage technology of the CCS using ocean region is Sub-seabed Geological Storage and dilution type Ocean Sequestration. These CCS Technologies has been developed in RITE. Especially, Research and development project of ocean sequestration technology was established the core technologies for example CO2 injection and dilution technology, prediction of drop and diluted CO2 and evaluation methods of biological influence of CO2. These core technologies were enabled a feasibility study of Ocean Sequestration technology as total system. These studies showed constructions of ocean sequestration system, and estimated sequestration costs and additional CO2 amount. Furthermore, in this evaluation, the ocean sequestration system without the influence on the marine organism was shown by scientists of the Ocean Sequestration Project of Japan. This evaluation and comparison study for atmospheric CO2 decreasing measure and ocean acidification mitigation measure was based on above results, and it was carried out using three dimensional numerical model with ocean circulation model (MOM: Modular Ocean Model), global carbon cycle model based on a lower trophic ecosystem model and one box atmospheric model. And the several scenarios were selected for evaluation of CCS efficiency. These scenarios ware targeted over CO2 emission based on S550 scenario and over emission were allocated to Geological Storage, Ocean Sequestration, other measure and no measure. Simulation results of Ocean Sequestration suggested efficiency for mitigation measure of increase atmospheric CO2 and Ocean Acidification. However, it was shown that the effect was different according to the ocean. Results of the simulation study showed "Geological storage without leakage is the best as the effect of measures". And it is suggested that "There is a possibility of suppressing the ocean surface acidification to more effective by combining dilution type ocean sequestration with subseabed geological storage". The effectiveness of ocean sequestration and geological storage was shown to some degree by this research. It is necessary to re-examine the use of the ocean model of a high resolution and the emission scenario of CO2, and to show the result with higher reliability.
An artificial mound was settled in the shallow ocean to enhance vertical mixing of nutrients and consequent primary production. It is expected that this technology contributes to the biological fixation of CO2 in the ocean. The turbulent mixing generated by the interaction between tidal currents and the mound was numerically simulated by using large eddy simulation in the cases of spring and half tides. The energy dissipation rate calculated from the numerical simulation shows a large horizontal variation when the tidal speed is large and a clear enhancement by the mound can be seen. The comparison between numerical result and the measurement implies that the location of the measurement was not included in the region of large energy dissipation. The vertical diffusivity was estimated from the numerical result to roughly quantify the vertical diffusive velocity of nutrients, which was enhanced up to 10−6–10−5 m s−1 when the tidal speed is its maximum, while it was 10−7 m s−1 when the effect of the mound is little .
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