Ocean sequestration technique of CO₂ may not be able to replace the cut of CO₂ emission itself, but can be one of quick-effect measures against the climate warming, elevation of sea level, and other influences of the global climate changes due to greenhouse gas accumulation in the atmosphere. Environmental effects of CO₂ ocean sequestration on surrounding sea areas must be properly assessed. One of the proposed methods consists in releasing CO₂ from onshore plants through pipeline at pre-determined depth in the ocean. In another, CO₂ may be continuously released into the middle depth from a ship cruising at a slow speed (Ozaki, 2001). In alternative methods, CO₂ may be deposited on the deepest sea bottom where no current and turbulence are considered to exist. In order to examine the feasibility of CO₂ sequestration technique, we followed the behavior of CO₂ released into the Pacific Ocean using the flow field discussed in the chapters above. We analyzed a case in which CO₂ generated by electric power plants is released through a pipeline at a fixed point in the ocean.

　

　

Total CO₂ emission of Japan in 1999 was billion tons (as CO₂), according to a report published by Environment Ministry in 2001. This amount exceeds by about 0.046 Gt (as C) the targeted cut of emission stated in COP3 (6% cut from the reference year of 1990). We examined by numerical simulation the behavior of this excess CO₂ that might be continually introduced in a single cell of the Pacific Ocean for 50 years. Whole calculated sea area was 0 (μmol/kg) at the initial state. The site of introduction was supposed to be under the stratification layer (in this study we assume the 7^th layer) at the subarctic region of the Northern Pacific Ocean, where has the potential to absorb CO₂.

　

　

Behaviors of sequestrated CO₂ are calculated by the following equation:

　

　

Where C the total carbonate concentration (μmol/kg), t is time (s), K_H the horizontal diffusion coefficient 1.0x10⁶cm²/s, K_v the vertical diffusion coefficient (1.0 x 10cm²/s) and β(λ,ψ,t) the annual input concentration of CO₂, 1.26 x 10² (μmol/kg/yr). The value of C was calculated from the surplus over the targeted emission cut (0.046 Gt).

　

　

To consider the CO₂ sequestration, most important problem is even if the injected CO₂ can be saved in the ocean for a long time. From the viewpoint of marine ecology, an abnormally high CO₂ concentration in specific sea areas must be avoided. Effects on meiobenthos, small bottom-living creatures less than 1 mm with little mobility, such as nematodes and foraminiferans, have also to be taken into consideration. Table 2 shows that calculation results of the total amount of CO₂ reaching for the surface, maximum CO₂ concentration at the surface and ratio of CO₂ reaching for the surface layer after the 50 years continual discharging in the North Pacific Subarctic region, is well known to the CO₂ absorption areas. The different sites of injection cause the variation of the total amount of CO₂ reaching for the surface and maximum CO₂ concentration at the surface. In case of zonal sites variation, further eastern sequestration can suppress the amount of reaching the CO₂ in the sea surface layer. On the other hand, meridional sites changes do not influence the CO₂ concentration. These trends are same in the all test case of injection CO₂. Figure 2 shows vertical distribution of CO₂ concentration at latitude 170°E and longitude 52°N in case of injection at 7^th layer and Figure 3 shows vertical distribution of CO₂ concentration (μmol/kg) at latitude 160°W and longitude 52°N in case of injection at 7^th layer.

　

　

　

　

　

Figure 4 shows the surface distribution of CO₂ concentration when CO₂ was released at 7^th layer. CO₂ reaching the surface is advected and diffused westwards from the release point under the influence of North Pacific Current. It was confirmed that CO₂ hardly crossed the equator into the southern hemisphere although it dispersed extensively in Subtropical Circulation System.

　

　

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