iMonsoon

The Indian summer monsoon (ISM) occurs within the word’s strongest hydrological regime and its rainfall and wind patterns affect the livelihoods of billions of people. Globally, the area influenced by monsoon systems is predicted to increase over the 21st century as a result of anthropogenic temperature and greenhouse gas forcing. However, model uncertainty for projections of monsoon rainfall is high, and the instrumental record is too short to resolve natural monsoon variability and forcings. Many fundamental questions on the functioning and feedbacks of the ISM, which varies on seasonal to tectonic timescales, remain unanswered. Our ability to predict future responses of the ISM to warming and high CO2 is hindered by a limited geological perspective, and reconstructions of the monsoon from older time intervals with warmer mean climate states are needed. During the late Miocene (around 11 to 5 million years ago, Ma) global temperatures and CO2 levels are estimated to have been significantly higher than during the Pleistocene; this interval therefore represents an important analogue for future climate. The iMonsoon project aims to reconstruct past climate and ISM variability during the warm late Miocene via the application of multiple geochemical and micropaleontological proxies to a new unique sediment core from the Bay of Bengal (IODP Site U1443), located in the core convective region of the ISM. In this single sedimentary sequence, we will reconstruct orbital to secular timescales changes in global climate (deep-sea temperature/ice volume), forcing mechanisms (surface ocean CO2 concentration) and parameters sensitive to the ISM (sea surface productivity, stratification, and temperature), producing the first reference record for this key interval. Global climate will be reconstructed via the analysis of stable isotopes in benthic foraminifers, and the use of paired stable isotope and trace element analyses in planktic foraminifers will allow us to assess upper water-column structure. Using calcareous nannofossil assemblages, we will reconstruct primary productivity and at the same time gain new insights into biotic evolutionary responses to changing climate. A unique aspect of this project will be the coeval reconstruction of CO2 concentrations, achieved by the continued development of a new proxy using coccolith geochemistry. These marine records, the first of their kind from the Miocene Indian Ocean, will be compared with new simulations of Miocene climate using the IPSL-CM6VLR model. These simulations will model the impact of changes in CO2 and orbital parameters on ISM intensity and productivity. This will allow us to better understand the mechanisms driving identified climate changes and potential monsoon-climate feedbacks in a warm background climate state. Results from this project will contribute to answering important questions in the field, namely (1) the sensitivity and timing of changes in monsoon circulation relative to external insolation forcing and internal boundary conditions including the export of latent heat from the southern hemisphere, the extent of global ice volume, and greenhouse gas concentrations, and (2) the timing and conditions under which monsoonal circulation initiated and evolved, and (3) the degree of coupling between the various subsystems of the Asian monsoon. This project will lead to the establishment of the PI’s research theme within the group at CEREGE, increasing the scope of paleoclimate research already carried out at this world-class institute. It will also provide her with the means to establish a research group centred on this theme, to create valuable long-lasting collaborations in the national and international communities, and to carry out research at a high level.