Shelf and coastal regions are at the interface between continents (impacted by human activities) and the open ocean (the main regulator of our planet’s climate and its biogeochemical cycles). The shelf-sea carbon pump largely relies on lateral transport to remove atmospheric CO2 from the ventilated surface waters and sequester it at depth. A good understanding of the physical transport processes in coastal regions and their impact on the ecosystem dynamics is therefore not only important for future climate predictions but also has a more immediate relevance (e.g. knowledge of local transport is necessary for the creation of marine protected areas, the management of spills, or the mitigation of harmful blooms events, etc.).<br/>SeaQUEST will study the horizontal transport and cross-shelf exchange processes including their effect on the biogeochemistry in the coastal zone around the Gulf of Lion (GoL) off the French Mediterranea coast, a highly productive area and important feeding ground for fish, birds, and mammals, both resident and migratory. The main goal of SeaQUEST is to examine the role of the Northern Current as a physical barrier to cross-shelf transport and the effect of its seasonal variability on the local biogeochemistry and plankton dynamics at meso- and sub-mesoscales. This will be achieved through a highly interdisciplinary approach employing a range of methods and data (numerical simulations, in situ and satellite observations). SeaQUEST will provide new insights into the ecosystem functioning and biological-physical interactions in a highly productive and economically important coastal area which is also one of the main tourist destinations worldwide. The results will therefore be of broad relevance to a variety of stakeholders including decision makers and local managers.