Interactions of the northern and southern branches of the thermohaline circulation

摘要

Coarse resolution models are used to investigate the influence of Southern Hemisphere processes on the northern branch of the thermohaline circulation. The link between the zonal wind stress at the latitude of Drake Passage and the production of deep water in the Northern Hemisphere is explored. Transient studies are conducted that illustrate the transmission of the wind generated signal from the Southern Hemisphere to the northern sinking region. Mixed-boundary condition experiments are conducted in a number of model configurations. The results of the OGCM mixed boundary condition experiments are investigated using simple box models. Two scenarios are presented to produce oscillations that are similar to deep-decoupling oscillations in the presence of continued AABW production. First, the high northern latitudes are subjected to a melt pulse/retreat pattern of freshening. Second, stochastic forcing is applied to the high northern latitude surface fresh water flux. In two-basin mixed boundary condition experiments, cooling the climate is seen to result in deep-decoupling type oscillations under stochastic forcing that produced no such variability in a warmer climate.