Present-day climate variability in the tropical Atlantic - A model for paleoclimate changes?

Paleoproxy records of the Holocene and last glacial period suggest that the meridional position of the Atlantic Intertropical Convergence Zone (ITCZ) and hence the thermally direct circulation in that region changed significantly in the past, a behavior similar to that of a leading mode of interannual-decadal climate variability in the present-day tropical Atlantic. This chapter explores how knowledge of this mode of variability may be usefully employed to advance hypotheses for understanding tropical Atlantic paleoclimate change. A review of past coupled general circulation model (CGCM) studies reveals that change to the Atlantic ITCZ meridional position is pervasive in two situations of paleoclimate interest; namely, modification of the Atlantic thermohaline circulation, and adjustment to last glacial maximum (LGM) boundary conditions. Comparison of atmosphere-ocean general circulation model LGM simulations from the Paleoclimate Modeling Intercomparison Project (PMIP) shows, however, that the magnitude of the latter adjustment is model dependent. Accurate paleoproxy records of tropical Atlantic climate may therefore be able to provide crucial constraints on acceptable coupled model behavior.