Surface coastal circulation patterns by in-situ detection of Lagrangian coherent structures

Coastal transport and cross-shelf exchanges are important factors in controlling the dispersal of human and river discharged pollutants, as well as the advection of nutrients and larvae. Altimetry-based Lagrangian techniques provide accurate information on horizontal transport in the open ocean but are unreliable close to the coast. In order to circumvent this problem, during the Lagrangian Transport Experiment 2010 campaign (Latex10, 1-24 September 2010) transport structures in the western Gulf of Lion were investigated with an adaptive sampling strategy, combining satellite data, ship-based ADCP measurements, and iterative Lagrangian drifter releases. The sampling strategy was able to identify errors in the surface transport patterns derived from altimetry, and to track with in-situ observations attractive and repelling Lagrangian coherent structures for a period of 12 days. The structures maintained a corridor ∼10 km-wide, roughly parallel to the coast, along which waters from the continental shelf leave the gulf. This is confirmed by high-resolution SST imagery. The use of this sampling strategy to explore surface transport structures may provide important information for the environmental management of coastal regions, and may serve for validating future coastal altimetric products.