Magdalena River in Colombia is the biggest freshwater input into the Caribbean Sea, with 7 211 m3s-1 or 227,4 km3y-1 (1). This discharge interacts with wind-driven currents and mesoscale eddies and is assumed to be an important component for the unique La Guajira Upwelling System (GUS). So far, however, the complex patterns of fresh and saltwater influence, nutrient cycles, plankton distribution and sediment deposits along the coast, on the shelf and in open sea this is only partially understood at best. In this Region of Freshwater Influence (ROFI), circulation is a complex convergence of mesoscale (Panamá-Colombia Gyre, Panamá countercurrent, GUS) and sub-scale (fronts and vortices) processes (2, 3, 4, 5). Understanding how these processes are dynamically related will enable the analysis of ecosystem connectivity, including geomorphology, sediment transport pathways, nutrient cycles and plankton productivity in the present and in the past. The Magdalena River input to the Caribbean Sea is not only significant in terms of fresh water, sediments, and nutrients, but also in contaminants (6). With fluxes exceeding 186 000 t y-1 and 47 000 t y-1, respectively, the Magdalena River is the most important external source for Phosphorus (P) and Nitrogen (N) to the Caribbean Sea (7). Such nutrient inputs significantly influence the behavior of biological communities in the estuary and river plume. However, detailed knowledge of the distribution, transport and turnover of nutrients and, therefore, biological communities is lacking. A very important aspect to be investigated by this project is the relationship between the freshwater discharge and the GUS. The GUS has the highest upwelling volume of the western boundary systems (8), but low chlorophyll concentration. The cause is not completely understood even though some possible explanations have been proposed (8, 9, 10). Some evidence suggests that seasonally and inter-annually, waters from the Magdalena River reach the GUS (1,2, 11, 12). The effects of this river-upwelling integration are unknown, but theoretically, during these events the low salinity waters from the river may favors stratification, limiting the upwelling and its associated productivity. These effects can be understood knowing the relation between circulation, primary productivity, biogenic sediment production and sediment accumulation on the sea floor. Additionally, an historical reconstruction of sediment accumulation and composition will reveal the reconstruction of climatic conditions at different time scales. Thus, selective views of the involved components in this ROFI do not allow knowledge gain as they ignore mutual interactions. We propose a comprehensive study of the system through an interdisciplinary approach. This proposal is based on a research cruise approved to be carried out by a group of German and Colombian institutions with the German research vessel Maria S. Merian. Due to the Covid-19 global emergency, the date of the cruise was postponed to 2021. We jointly intend to prepare an international proposal to finance the participation of the scientists on the cruise, and the commitments and challenges that it implies (the analysis of the samples taken during the expedition and the evaluation of the results and measured values). During the cruise we will sample from the mouth of the river to the outer extension of the plume of freshwater and over the GUS, to investigate the main processes of land-sea interaction that take place in this tropical ROFI. Knowledge generated with the proposal will have impact to the food security of La Guajira department and to environmental concerns of the Magdalena department. Additionally, the proposal will educate human resources at highest level, and will maintain international collaboration with German colleagues and institutions.