Rapid Transitions of the Thermohaline Ocean Circulation

Abstract

This chapter discusses the stability of the Atlantic thermohaline circulation with special emphasis on the critical thresholds and state transitions found in model experiments. The thermohaline ocean circulation is a major heat transport mechanism which causes the relatively mild climate in the North Atlantic region (including Europe) in the modern times. The formation of North Atlantic Deep Water and the associated large-scale meridional transports in the Atlantic are maintained by a positive salinity feedback (first identified by Stommel in 1961). A second positive feedback is responsible for the tendency of deep convection to reoccur in the same regions. These two feedbacks are the main reason for the non-linear behaviour of the thermohaline ocean circulation found in models; their characteristic processes, time and length scales are discussed. Simulations of plausible circulation changes during the last glacial maximum and due to future greenhouse warming are presented.