The role of the individual air-sea flux components in CO_2-induced changes of the ocean's circulation and climate

Abstract

In this study we investigate the role of heat, freshwater and momentum fluxes in changing the oceanic climate and thermohaline circulation as a consequence of increasing atmospheric CO_2 concentration. Two baseline integrations with a fully coupled ocean atmosphere general circulation model with either fixed or increasing atmospheric CO_2 concentrations have been performed. In a set of sensitivity experiments either freshwater and/or momentum fluxes were no longer simulated, but prescribed according to one of the fully coupled baseline experiments. This approach gives a direct estimate of the contribution from the individual flux components. The direct effect of surface warming and the associated feedbacks in ocean circulation are the dominant processes in weakening the Atlantic thermohaline circulation in our model. The relative contribution of momentum and freshwater fluxes to the total response turned out to be less than 25%. Changes in atmospheric water vapour transport lead to enhanced freshwater input into middle and high latitudes, which weakens the overturning. A stronger export of freshwater from the Atlantic drainage basin to the Indian and Pacific ocean, on the other hand, intensifies the circulation. In total the modified freshwater fluxes slightly weaken the Atlantic thermohaline circulation. The contribution of the modified momentum fluxes has a similar magnitude, but enhances the formation of North Atlantic deep water. Salinity anomalies in the Atlantic as a consequence of greenhouse warming stem to almost equal parts from changes in net freshwater fluxes and from changes in ocean circulation caused by the surface warming due to atmospheric heat fluxes36 refs.Available from TIB Hannover: RR 1347(263) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman