THE PAST DYNAMICS OF THE AFRICAN AND INDO-ASIAN MONSOONS

The monsoon system is characterized by a seasonal meridian swing in winds and precipitation which produces dry winters and humid summers in the Tropics. This system arises from the difference in heat that is seasonally created between the oceans and the continent and between the two hemispheres of the world. It is a key mechanism in the world’s current and past climatic systems because it plays and essential role in the global distribution of heat and humidity.

Paleoclimatic studies show that the dynamics of the regional monsoon systems have varied over time, particularly during the Quaternary, as a function of the earth’s orbital parameters and insolation forcing. It appears that complex processes and interactions involving, for example, the extent of the ice caps, changes in atmospheric pCO₂ and ocean dynamics, have also contributed to the variability of monsoon dynamics over time. On the continents, past variations in precipitation and wind regimes determined the vulnerability of rocks to erosion by impacting on river flows, vegetation type and soil types. These variations thus affect chemical alteration in the source zones, the mobilization of sedimentary material on the continents and the transfer of this material, by water and/or air, to the ocean basins.  In the oceans, they cause significant changes in the dynamics of surface waters and particularly in the depths of the thermocline/nutricline which in turn have a considerable impact on primary producers (particularly coccolithophores). It is in this context that a multi-tool study (using sedimentological, mineralogical, geochemical and micropaleontological analyses) of sedimentary archives retrieved for African, Indian and Asian monsoon contexts, allows us to examine, from various angles, the issue of variability in the Monsoon system at various spatial and temporal scales.