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Subject: freshwater input ×

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    The modern and glacial overturning circulation in the Atlantic ocean in PMIP coupled model simulations
    (München : European Geopyhsical Union, 2007) Weber, S.L.; Drijfhout, S.S.; Abe-Ouchi, A.; Crucifix, M.; Eby, M.; Ganopolski, A.; Murakami, S.; Otto-Bliesner, B.; Peltier, W.R.
    This study analyses the response of the Atlantic meridional overturning circulation (AMOC) to LGM forcings and boundary conditions in nine PMIP coupled model simulations, including both GCMs and Earth system Models of Intermediate Complexity. Model results differ widely. The AMOC slows down considerably (by 20–40%) during the LGM as compared to the modern climate in four models, there is a slight reduction in one model and four models show a substantial increase in AMOC strength (by 10–40%). It is found that a major controlling factor for the AMOC response is the density contrast between Antarctic Bottom Water (AABW) and North Atlantic Deep Water (NADW) at their source regions. Changes in the density contrast are determined by the opposing effects of changes in temperature and salinity, with more saline AABW as compared to NADW consistently found in all models and less cooling of AABW in all models but one. In only two models is the AMOC response during the LGM directly related to the response in net evaporation over the Atlantic basin. Most models show large changes in the ocean freshwater transports into the basin, but this does not seem to affect the AMOC response. Finally, there is some dependence on the accuracy of the control state.
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    On freshwater-dependent bifurcations in box models of the interhemispheric thermohaline circulation
    (Abingdon : Taylor and Francis Ltd., 2002) Titz, S.; Kuhlbrodt, T.; Rahmstorf, S.; Feudel, U.
    Conceptual box models of the interhemispheric thermohaline circulation are studied with respect to bifurcations. Freshwater fluxes are the main control parameters of the system: they determine the stable states and transitions between stable states of the large-scale thermohaline circulation. In this study of interhemispheric box models both numerical and analytical methods are used to investigate transition mechanisms of the thermohaline circulation. The box model examined first is an interhemispheric four-box model. It is shown that the two bifurcations where the present THC can become unstable, the saddle-node and the Hopf bifurcation, depend in a different way on hemispheric freshwater fluxes. A reduction of the model variables leads to the conclusion that two fixed freshwater fluxes between three surface boxes are the model feature responsible for the bifurcation behavior found. The significance of the Hopf bifurcation for the stability of the thermohaline circulation is discussed.