The global carbon cycle represents the collection of complex biogeochemical processes that influence our climate and link all carbon pools on Earth. Soils play a very active and key role in this cycle, as upon sequestration in marine sediments they act as long-term sink of atmospheric CO2. A large part of organic carbon (OC) stored in soils is continuously mobilized and either returned to the atmosphere or transported by rivers to the oceans. However, the fate and residence time of soil OC within in a river basin is often overlooked, and our understanding of potential feedback mechanisms to our climate remains far from complete. In this project I aim to determine the origin of soil OC in a river, the transformations that soil OC undergoes during its transport from land to sea, the duration of this transport, as well as to assess the factors that control these processes. For this I will utilize a suite of soil bacterial membrane lipids, branched glycerol dialkyl glycerol tetraethers (brGDGTs), as specific molecular tracers of soil OC. River-transported brGDGTs stored in continental margin sediments may reflect the integrated climate history of the river basin, as their initial distribution in soils is determined by temperature and soil pH. The novelty of my approach lies in the combination of these molecular tracers with an array of advanced isotopic techniques (13C, D/H, 14C) and inorganic chemistry (Neodymium isotopes). This allows me to monitor soil OC during its complete journey from terrestrial source to sedimentary sink. The new information resulting from this project will deepen our understanding of the role of soils in OC storage and export, and thus the carbon cycle, and will improve our interpretation of paleoclimate records based on down-core variations in brGDGTs preserved in marine sediments.