| Summary: | The principal objective of this study is to determine whether or not the penetration of a passive tracer is analogous to the penetration of a greenhouse-gas-induced heating. The Atmosphere-Ocean General Circulation Model (A-O GCM) has been used to study CO$\sb2$-induced climate change and the penetration of passive tracers into the world ocean. The present climate and a 2 x CO$\sb2$ climate have been simulated. The passive tracers tritium, CFC-11, CFC-12 and a "passive CO$\sb2$-induced heating" are simulated. The CO$\sb2$-induced active and passive warmings are larger in the subtropics and high latitudes than in the tropics. The largest difference between the active and passive CO$\sb2$-induced heatings occur in the North Atlantic deep ocean, with maximum cooling about $-$1.5$\sp\circ$C for the active case in layer four of the ocean (1150m). There is no hemispherically asymmetric warming as that found by Manabe et al. (1990) and Stouffer et al. (1990). The convective overturning and large-scale sinking motion are responsible for the large penetration of CO$\sb2$-induced warming in high latitudes. The CO$\sb2$-induced circulation changes show that the North Atlantic thermohaline circulation is significantly weakened due to the penetration of CO$\sb2$-induced heating. Associated with this change, the strength of North Atlantic conveyor belt is reduced, which results in a large warming in the upper ocean and cooling in the deep layers. The characteristic response time ranges from 40-50 years for the active CO$\sb2$-induced climate change, and 70-160 years for passive CO$\sb2$-induced climate change. The physical processes controlling the geochemical tracer penetration are very similar to those for the CO$\sb2$-induced heating. There is no a single tracer which penetrates into the ocean exactly like the active CO$\sb2$-induced heating in terms of distribution, transport or physical process. CFCs may be the best candidate as a surrogate for the CO$\sb2$-induced oceanic climate study. The model is capable of simulating the observed ocean-atmosphere pCO$\sb2$ difference ($\Delta$pCO$\sb2$) in most areas. However, the model cannot simulate the observed magnitude and detailed geographical distribution of $\Delta$pCO$\sb2$ because they are also determined by the organic and biological processes which are neglected in the present study. (Abstract shortened with permission of author.)
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