Project A10

Temporal variations in upper ocean stratification strongly influence the heat and gas exchange between the atmosphere and the ocean interior as well as ENSO (El Niño-Southern Oscillation) variability, and thus global climate change. This project builds on the hypothesis that changes in the strength of Atlantic meridional overturning circulation can trigger changes in tropical thermocline depth as suggested by theoretical considerations and coupled climate models. Weakening of the overturning circulation causes a deepening of the thermocline, and vice versa, with largest effects in the Atlantic (Huang et al., 2000; Timmermann et al., 2005). It will be tested whether this mechanism operated on different timescales (orbital-to-millennial) and climate background states. Comparisons of sediment records from doldrums- (weakest tropical wind-stress) and upwelling-areas will permit isolation of circulation- from wind-induced changes in thermocline depth. The relevance of the outlined mechanism will be evaluated by combining proxy data and model results.