Norikazu Nakashiki

Response of the North Atlantic Thermohaline Circulation and Ventilation to Increasing Carbon Dioxide in CCSM3

Abstract The response of the North Atlantic thermohaline circulation to idealized climate forcing of 1% per year compound increase in CO2 is examined in three configurations of the Community Climate System Model version 3 that differ in their component model resolutions. The strength of the Atlantic overturning circulation declines at a rate of 22%–26% of the corresponding control experiment maximum overturning per century in response to the increase in CO2. The mean meridional overturning and its variability on decadal time scales in the control experiments, the rate of decrease in the transient forcing experiments, and the rate of recovery in periods of CO2 stabilization all increase with increasing component model resolution. By examining the changes in ocean surface forcing with increasing CO2 in the framework of the water-mass transformation function, we show that the decline in the overturning is driven by decreasing density of the subpolar North Atlantic due to increasing surface heat fluxes. While...

Density change of water due to dissolution of carbon dioxide and near-field behavior of CO2 from a source on deep-sea floor

Abstract CO 2 recovery from the flue gases of fossil energy power sources followed by ocean disposal should be carefully examined in terms of engineering and ecological constraints. For detailed assessment of ocean floor disposal options, the prediction of solute CO 2 behavior in the bottom ocean current is important for evaluating the degree of possible damage by the CO 2 to the benthic ecosystem. A water coexisting with liquid CO 2 in a 35-ml cell (at 3 °C, 343 atm) was sampled and introduced into a vibrating-tube type densitometer. After the density measurement the sample was expanded into a buret system, where the CO 2 can be determined volumetrically. Density increase of 0.00284 g/cm 3 per 1 wt.% CO 2 dissolution was observed, which corresponds to the CO 2 partial molar volume of 31.0 cm 3 /mole. A preliminary computer simulation experiment of CO 2 behavior around “CO 2 lake” formed on the deep ocean floor was conducted under the condition as follows: bottom water current; 5 cm/s, thickness of benthic boundary layer; 100 m, vertical eddy diffusivity in the benthic boundary layer; 100 cm 2 /s. The density flow regime was remarkably observed near the “CO 2 lake”.

Dispersion of CO2 injected into the ocean at the intemediate depth

Abstract The biological impact on the ambient marine environment should be assessed in the CO 2 injection at the intermediate depth. The long term dispersion (several decades) will also have a potential impact on the marine ecosystem in the wide area. The velocity field and dispersion of the substance in the North Pacific ocean at the intermediate depth were computed using an OGCM, and discussed with the comparison with the observed temperature, salinity and CFCs profiles. A model was applied to estimate the diffusion of the artificially injected CO 2 .

Lake-type storage concepts for CO2 disposal option

Many types of deep ocean storage of CO 2 have been proposed, and are classified into two groups: a deep ocean dissolution, and a deep ocean storage. The concepts of these storage systems are briefly reviewed. Problems and difficulties are discussed concerning deep ocean storage.

Calculation of artificial radionuclides in the ocean by an ocean general circulation model

The concentrations of three artificial radionuclides (90Sr, 137Cs and 239+240Pu) introduced into seawaters from global fallout were simulated from 1957 to 1994 by using an ocean general circulation model. The distributions of the calculated 137Cs and 90Sr concentrations were in good agreement with the observed concentrations. The vertical distribution of the calculated 239+240Pu concentration in the South Pacific also agreed with the observed data. However, the calculated 239+240Pu concentrations in the North Pacific water columns were significantly underestimated in comparison with the observed data, which strongly suggests the presence of additional sources of plutonium input to the North Pacific.

Effectiveness of ocean intermediate depth injection

The effectiveness of isolation (i.e., retention time) for the CO 2 injected at the North Pacific intermediate deep water was examined, based on the calculation of the annual mean circulation in the world ocean. Particle tracing was carried out to study the water mass movement at the intermediate depth in the North Pacific Ocean, which suggests that the CO 2 injection into 100 m depths of the North Pacific Ocean could provide an effective measure of the short term isolation of the collected CO 2

Effectiveness of ocean intermediate depth injection (Part 2)

Abstract The effectiveness of isolation of CO 2 injected in the North Pacific Ocean was discussed in the seasonal flow fields, which were computed on the bases of the seasonal change of wind, water temperature and salinity. A periodic annual flow field was estimated, where the seasonal change of flow was taken into account using the computed flow fields in four seasons. Particle tracking was also carried out in the periodic flow field over 200 years. The effectiveness of isolation was discussed, in comparison with the computational results in the annual mean flow fields.