Characterization of 3D coastal mesoscale structures and transports from multiplatform observations and a data reconstruction method

The role of coastal mesoscale variability in the modulation of surface along-shelf and cross-shelf exchanges in the SE Bay of Biscay has been demonstrated by several works, from land-based and satellite observations, including high resolution current fields from high-frequency (HF) radars. However, the characterization of physical processes and associated transports at subsurface levels from observations remains a challenge since observations are often too scarce to offer the required spatio-temporal resolution and coverage. In addition to the numerical modelling, the use of methods to reconstruct three-dimensional (3D) current fields from the combination of multiplatform data offers an alternative approach for the study of 3D properties of mesoscale coastal processes, and an improved background to explore bio-physical interactions. Studying the physical properties of coastal mesoscale structures at subsurface levels, where primary production and plankton concentration peak, is key to understand the coupling between physical and biological processes. In this work, we use a previously validated data-reconstruction method and different CMEMS products (coastal simulations, observations from HF radar, satellite, mooring) and glider data, to better characterize the 3D structure of a coastal mode-water eddy and its associated water volume transport. Different Lagrangian properties (maps of particle density, residence times, Lagrangian eddy kinetic energy) obtained at surface and subsurface levels provide a new insight into the water volume transports associated with the main coastal processes in the area.