Variability of the Indo-Asian monsoon and its impact on primary productivity since the Last Glacial Maximum: Local processes and global processes

India and Asia, as well as the tropical regions of the Indian and Pacific Oceans, are under the direct influence of a South West summer monsoon and a North East winter monsoon. In the past there is no doubt that these monsoon systems depended on the Earth’s orbital parameters and insolation forcing. However, complex processes and interactions within the Ocean-Atmosphere system (the extent of ice sheets, atmospheric pCO₂, the dynamics of the AMOC, ENSO, IOD, etc.), which are still poorly understood, probably also played important roles.

The aim of this thesis is to reconstruct, at a high temporal resolution, the dynamics of the Indian and Asian monsoons over the course of the last 25 ka and to gain an understanding of the natural forcing factors (pre-anthropic) responsible of their variations using a model-data comparison centred on changes in primary production. Particular attention is paid to coccolithophoric assemblages; coccolithophores are principal primary producers in the region and are sensitive to the monsoon dynamic directly impacting on the mixing zone (depth of the thermo/nutricline). This study is based on four sedimentary cores taken from the Gulf of Bengal, the Arabian Sea and the China Sea and uses IPSL marine biogeochemical models in order to compare the Indian and Asian systems and to better understand the concept of global monsoon in the past.

Stéphanie Duchamp-Alphonse, Christophe Colin

Chinese Scholarship Council (CSC)