Diagnosing cross‐shelf transport along an ocean front: An observational case study in the Gulf of Lion

Abstract

AbstractExchanges between coastal regions and the open ocean are often associated with intermittent and localized processes such as eddies, fronts, and filaments. Since these features are difficult to observe, their impact has been predominantly investigated using numerical models and remote sensing. In this study, satellite sea surface temperature maps, Lagrangian surface drifter trajectories, and ship‐based surveys of currents and hydrography from the Latex10 campaign are used to quantify cross‐shelf exchanges associated with a temperature front in the western Gulf of Lion. Satellite imagery and thermosalinograph sections provide the characterization of the various water masses associated with the front. Lagrangian drifter trajectories are used to identify the main transport structures and to quantify the velocity components associated with near‐inertial oscillations. These are removed from the instantaneous ADCP observations with which the cross‐shelf exchanges are then computed. The results indicate an average outflow of 0.074 ± 0.013 Sv and an inflow of 0.021 ± 0.006 Sv. Integrated over the 2 week lifetime of the front, such outflow induced a total export of ∼90 ± 14 km3 of water, indicating that three to four of such events are sufficient to completely renew the surface waters of the Gulf of Lion. The total import was ∼25 ± 7 km3, suggesting larger inflows at depth or in the eastern part of the gulf to maintain its volume balance. These in situ estimates represent a key term of comparison for the further development of numerical model‐based and satellite‐based studies of cross‐shelf exchanges associated with this type of processes.