Effects of Ice Albedo and Runoff Feedbacks on the Thermohaline Circulation

Abstract

Simple parameterizations of the ice albedo feedback and its implicit effect on the high-latitude river runoff have been added to the coupled atmosphere-ocean box model developed by Nakamura et al. The additional parameterizations introduce four new feedbacks into the model. The first is a stabilizing feedback between high-latitude albedo and the thermohaline circulation through influence on the temperature. In terms of the Newtonian cooling concept, introduction of this feedback is equivalent to allowing changes in the ?apparent equilibrium temperature.? The second and the third feedbacks are consequences of the first; the modified temperature profile affects the meridional transports of moisture and heat by atmospheric eddies, which form positive feedbacks with the thermohaline circulation as shown by Nakamura et al. The fourth is a stabilizing feedback between the thermohaline circulation and freshwater flux into the high-latitude ocean due to ice freezing or melting. The experiments show that the net effect of the four feedbacks is stabilizing in this idealized model when salinity or temperature are perturbed. However, it is destabilizing when the solar forcing is perturbed. The results suggest that accurate representation of the response of high-latitude hydrological paths to changing temperatures may be crucial to modeling the sensitivity of the thermohaline circulation.