M. Latif
Max-Planck-Institut für Meteorologie
Bundesstr. 55, D-20146 Hamburg, Germany

Analysis of sea surface temperature (SST) observations (Latif 2001) suggests a pan-oceanic in-teraction between the tropical Pacific and the Atlantic Ocean at multi-decadal time scales, such that periods of anomalously high SSTs in the eastern tropical Pacific are followed by a basin-wide SST dipole in the Atlantic Ocean with a time delay of a few decades (Figure 1). The SST anomaly structure in the Atlantic Ocean is reminscent of variations in the North Atlantic thermohaline circulation. The two ocean basins are linked through an "atmospheric bridge" involving anomalous fresh water fluxes. Based on the observational findings, the Atlantic thermohaline circulation may strengthen during the next decades in response to the strong decades-long increase in eastern tropical Pacific SST, which will have strong impacts on the climates of North America and Europe through changes in the North Atlantic. It has been shown in a recent paper (Latif et al. 2000) that changes in the tropical Pacific stabilise the North Atlantic thermohaline circulation (THC) in a greenhouse warming simulation, with the atmosphere serving as a coupling device between the two oceans. The proposed mechanism works as follows: The long-term changes in the eastern tropical Pacific SST induce changes in the fresh water flux over the tropical Atlantic, which will lead to anomalous sea surface salinities (SSSs) in the tropical Atlantic Ocean. The SSS anomalies are advected poleward by the mean ocean circulation, eventually affecting the density in the sinking region of the Northern Hemisphere, thereby affecting the convection and the strength of the thermohaline circulation.