The main objective of the LAgrangian Transport EXperiment (LATEX) project was to study the influence of coastal mesoscale and submesoscale physical processes on circulation dynamics, cross-shelf exchanges and biogeochemistry in the western continental shelf of the Gulf of Lion, Northwestern Mediterranean Sea. LATEX was a five-year multidisciplinary project based on the combined analysis of numerical model simulations and multi-platform field experiments. The model component included a ten-year realistic 3D numerical simulation, with a 1 km horizontal resolution over the gulf, nested in a coarser 3 km resolution model. The in situ component involved four cruises, including a large-scale multidisciplinary campaign with two research vessels in 2010. This review concentrates on the physics results of LATEX, addressing three main subjects: 1) the investigation of the mesoscale to submesoscale processes. The eddies are elliptic, baroclinic and anticyclonic; the strong thermal and saline front is density-compensated. Their generation processes are studied; 2) the development of sampling strategies for their direct observations. LATEX has implemented an adaptive strategy Lagrangian tool, with a reference software available on the web, to perform offshore campaigns in a Lagrangian framework; 3) the quantification of horizontal mixing and cross-shelf exchanges. Lateral diffusivity coefficients, calculated in various ways including a novel technique, are in the range classically encountered for their associated scales. Cross-shelf fluxes have been calculated, after retrieving the near-inertial oscillation contribution. Further perspectives are discussed, especially for the ongoing challenge of studying submesoscale features remotely and from in situ data.

The interactions between ageostrophic processes and large scale dynamics in the western part of the Gulf of Lion (NW Mediterranean) play a fundamental role in regulating water exchanges between the continental shelf and the open sea. The dominant regimes emerging from these interactions were successfully characterized during the Lagrangian Transport Experiment (LATEX, 2008-2010) thanks to a multi-platform approach which included in-situ observations, satellite measurements and numerical model simulations. During the Latex10 campaign (September 1-24, 2010), in-situ Lagrangian Coherent Structures reconstructed from drifter trajectories allowed to identify an alongshore corridor through which coastal waters escaped the Gulf. Satellite imagery indicated that the offshore boundary of the corridor was associated with a strong frontal region. Glider profiles allowed to reconstruct the vertical structure of the front, and ship-based ADCP currents to estimate the associated horizontal fluxes. Realistic numerical simulations showed that this regime alternates with periods during which the circulation is dominated by coastal anticyclones (also observed in previous campaigns). Model results, along with a regional satellite altimetry product, allowed to characterize the influence of the two regimes in regulating cross-shelf exchanges.

We investigate the dynamics of a coastal anticyclonic eddy in the western part of the Gulf of Lion (GoL) in the northwestern Mediterranean Sea during the Latex campaign in the summer 2009 (Latex09). The sampling strategy combines SST satellite imagery, hull-mounted ADCP data, CTD casts and drifter trajectories. Our measurements reveal an anticyclonic eddy (Latex09 eddy) with a diameter of ~23 km and maximum depth of 31 m, centered at 3°34'E - 42°33'N. We use a high resolution, 3-dimensional, primitive equation numerical model to investigate its generation process and evolution. The model is able to reproduce the observed eddy, in particular its size and position. The model results suggest that the Latex09 eddy is induced by a large anticyclonic circulation in the northwestern part of the GoL, pushed and squeezed toward the coast by a meander of the Northern Current. This represents a new generation mechanism that has not been reported before. The post generation dynamics of the eddy is also captured by the model. The collision of the Latex09 eddy with Cape Creus results in a transient structure, which is depicted by the trajectories of two Lagrangian drifters during Latex09. The transient structure and its advection lead to a transfer of mass and vorticity from the GoL to the Catalan shelf, indicating the importance of mesoscale structures in modulating such exchanges in the region.

The general circulation in the northwestern Mediterranean Sea is characterized by a cyclonic circulation. The northern part of this gyre is formed by the Northern Current (NC), which flows along the continental slope from the Ligurian Sea towards the Catalan Shelf. The NC has an important influence on the Gulf of Lion (GoL), a large continental margin in the northern part of the basin. The NC constitutes an effective dynamical barrier which blocks coastal waters on the continental shelf. The western part of the GoL is a key region for regulating the outflow from the continental shelf to the Catalan Basin. These exchanges are mainly induced by partially ageostrophic processes originating from the interaction between the NC and mesoscale activity like meanders, filaments and eddies. Both GoL and Catalan shelf are characterized by an intense mesoscale activity. Eddies in the GoL are baroclinic structures extending throughout the mixed layer (30 to 50m), often elliptic in shape and about 20-30km in diameter. Catalan eddies are characterized by a vertical extension between 70 and 100m and a diameter of about 45km. The LAgrangian Transport EXperiment (LATEX, 2008-2011) was designed to study the mechanisms of formation of anticyclones in the western part of the GoL and their influence on cross-shelf exchanges. Mesoscale anticyclones have been observed in the western part of the GoL and over the Catalan shelf by the combined use of data from satellite observations, in situ measurements and numerical modeling. Recent numerical experiments show an anticyclonic circulation extending over a large part of the coastal area (latitudinal range : 41°50' to 43°N ; longitudinal range : 3°10' to 4°10'E). Interaction with a meander of the NC induces the separation of this circulation in two different eddies, one in the GoL and the other in the Catalan shelf. These eddies exhibit strong interaction between them, resulting in important exchanges between the two coastal regions. On one hand the Catalan eddy causes a heat transfer to the GoL; and, on the other hand, the interaction between the GoL eddy and a topographic barrier (Cap Creus) leads to a transfer of energy to the Catalan eddy. In order to quantify this exchange, a balance of kinetic energy has been analyzed from the model results. Numerical results are also discussed in comparison with in situ observations collected during the Latex09 campaign (August 24-28, 2009). The analysis of Sea Surface Temperature (SST) satellite images, Acoustic Doppler Current Profiler (ADCP) and Lagrangian drifter trajectories, confirmed the above interpretation derived from numerical model.

We investigate the dynamics of a coastal anticyclonic eddy in the western part of the Gulf of Lion (GoL) in the northwestern Mediterranean Sea during the Latex campaign in the summer 2009 (Latex09). The sampling strategy combines SST satellite imagery, hull-mounted ADCP data, CTD casts and drifter trajectories. Our measurements reveal an anticyclonic eddy (Latex09 eddy) with a diameter of ~23 km and maximum depth of 31 m, centered at 3°34'E - 42°33'N. We use a high resolution, 3-dimensional, primitive equation numerical model to investigate its generation process and evolution. The model is able to reproduce the observed eddy, in particular its size and position. The model results suggest that the Latex09 eddy is induced by a large anticyclonic circulation in the northwestern part of the GoL, pushed and squeezed toward the coast by a meander of the Northern Current. This represents a new generation mechanism that has not been reported before. The post generation dynamics of the eddy is also captured by the model. The collision of the Latex09 eddy with Cape Creus results in a transient structure, which is depicted by the trajectories of two Lagrangian drifters during Latex09. The transient structure and its advection lead to a transfer of mass and vorticity from the GoL to the Catalan shelf, indicating the importance of mesoscale structures in modulating such exchanges in the region.