Though decoupled in time and space in the ocean, Si and C cycles are closely linked. The role played by these elements on climate and marine ecosystems is essential and their biogeochemical cycle is undergoing dramatic changes. MuSiCC proposes to bring unique know-how, developed abroad by the applicant, to UPMC, a leading French university where he now has a permanent position. This project is complementary to the excellence already developed at UPMC. Two research axes are proposed:– Si and C cycles in the Southern Ocean (SO). The specific objectives are to quantify for the different biogeochemical provinces of the SO, the seasonal evolution of: Si nutrient supply, diatoms’ production, C and Si export out of the surface layer, mesopelagic remineralisation and the ultimate C export to the deep ocean.– Si cycle at continent – ocean interfaces. This axis is more exploratory and we plan to bring new elements to answer the following questions: What is the contribution to Si cycle of sedimentary diagenesis in the continental margins? What is the contribution and fate of riverine biogenic Si fluxes to the ocean? How do anthropogenic pressures affect the Si cycle in estuarine and coastal zones?MuSiCC is based on the implementation of an advanced multi-proxy approach integrating several temporal scales and processes:- The natural isotopic composition of Si allows identification of Si source and quantitative estimates of Si fluxes and mixing at annual scale.- Si isotopic dilution is the most precise and sensitive technique to determine short-term uptake – dissolution fluxes.- mesopelagic Ba content is one of the very few proxies to provide estimates of carbon remineralisation fluxes.Complementing the salary funding already obtained, MuSiCC CIG would provide an ideal framework, based on international collaboration, to set up this approach at UPMC, would make significant progress on these issues within the project lifetime and facilitate integration of the applicant.