Coastal wetlands, from the continuum of backshore marshes to the intertidal zone, are widely represented on the French Channel-Atlantic coast. These highly productive environments receive continental inputs and can capture and sequester carbon (C) sustainably. The ANR CABESTAN project, selected within the framework of the PEPR FairCarboN, aims to address knowledge gaps regarding the processes and forcings governing carbon fluxes in these environments, particularly surface-atmosphere fluxes of CO2 and CH4. How do carbon uptake and recycling processes at tidal, diurnal, and seasonal scales influence long-term carbon sequestration? How does carbon dynamics evolve across salinity and eutrophication gradients, from the intertidal zone to salt marshes? In this multidisciplinary study context (30 researchers from 9 laboratories), the LMD will focus on surface-atmosphere exchange processes of CO2 and CH4 at the land-sea interface using multiple in situ observations (flux chamber, eddy-covariance) and remote sensing (hyperspectral imaging, lidar). In particular, the 3D lidars TERA (T, H2O), COWI (wind, CO2), and MEDAL (CH4) will be utilized to upscale energy and carbon fluxes from the small scale (m) to the spatial resolution of the LSM ORCHIDEE model (km).