Understanding the role played by the combined physical-biogeochemical dynamics at (sub)-mesoscales in exchanges of matter and energy between coastal and open sea areas. The LATEX strategy is based on selective and combined use of numerical modelling and in situ observations (Lagrangian floats, SF6, shipboard ADCPs, ADCP moorings, satellite images, gliders and coastal radars). The main objective of LATEX is to study the impact of an eddy structure at (sub)mesoscale, which is chronically present in the western part of the Gulf of Lion, in interaction with the North Mediterranean current(NMC)on trends in the distribution of conservative tracers and biogeochemical properties. Thanks to this strategy, LATEX should provide answers to the following questions: - Is this type of structure likely to significantly affect the horizontal transfer of matter between the continental shelf and the NMC? - What are the consequences for biogeochemical cycles of the structure's interaction with the NMC? - How do CO2 concentrations evolve within the eddy throughout its life cycle? - How does this type of (sub)-mesoscale coastal eddy act in structuring of plankton communities and the variability in primary production observed in the study zone? - Are the amounts of matter transferred by (sub)-mesoscale structures significant with respect to that displaced by the general circulation on seasonal and annual scales? The related project is called LATEX (LAgrangian Transport Experiment).

<p>Studying eddies related to water circulation in the Gulf of Lion. The LOPB and LOMIC labs will implement a technique never used before for coastal systems, i.e. tracking of a water mass using the chemically inert compound sulphur hexafluoride (SF6). After injecting the tracer from aboard RV Suroît, the substance's dissemination will be estimated thanks to real-time measurements performed on board. To monitor the eddy structure, RV Suroît will be accompanied by RV Tethys II. Several innovative devices or systems will be deployed simultaneously (measuring currents using Doppler acoustic profiler (with the moorings already in the zone since 2009 and the 2 vessels' shipboard current meters); Measuring surface currents using an array of HF radars installed onshore; several satellite-monitored drifting buoys, including a CARIOCA buoy which will continuously log the physical parameters and CO2 trends near the surface; autonomous underwater gliders fitted with various biogeochemical sensors; real-time satellite observation of surface temperature and phytoplankton concentrations; and operational numerical modelling. The measurements will be analyzed on board and will be used to locate the eddy's position in order to guide the vessels to the drifting research zone. The original aspect of LATEX is that it combines expertise in physical oceanography and marine biogeochemistry to try and penetrate the mystery of these mesoscale structures and particularly to assess the role they play in transfer of matter between the coastal zone and the open sea. The fate of organic matter will be closely observed during this monitoring of the drifting eddy structure to understand how the biogeochemical properties (quality of organic matter, stoichiometry of particulate matter, primary and bacterial production) evolve over time in this volume of water enclosed by physical processes.</p>