Spatial and Seasonal Distributions of Frontal Activity over the Continental Shelf in the Bay of Biscay - Focus on Density Fronts in Winter

Özge Yelekçi, IFREMER, DYNECO - Laboratoire de Physique Hydrodynamique et Sédimentaire, Plouzané, France, Guillaume Charria, IFREMER, Plouzané, France, Xavier Capet, Université Pierre et Marie Curie, LOCEAN , IPSL, Paris, France, Gilles P Reverdin, Sorbonne Université - CNRS/IRD/MNHN, LOCEAN, Paris, France, Joël Sudre, LEGOS/CNRS, SYSCO2, TOULOUSE, France and Hussein Yahia, GeoStat team, INRIA Bordeaux Sud-Ouest, Talence, France
Abstract:
Recent observations over the continental shelf in the Bay of Biscay (in the Eastern Atlantic along French and Spanish coasts) revealed an expected complex small scale (O(1km)) activity with high frequency variations. A dataset of 11 years’ (2003 to 2013) Sea Surface Temperature (SST) remotely sensed by MODIS sensor onboard Aqua and Terra satellites has then been studied to detail the spatial and seasonal distributions of fronts over the continental shelf North of 45°N in the Bay of Biscay.

Observed spatial and temporal patterns of frontal activity have enabled the characterization of fronts based on their driving mechanisms. Results are in agreement with previous studies defining the location and seasonality of tidal fronts in the Ushant region and the frontal activity close to the internal tide generation area along the shelf break.

This analysis also highlighted a third group of fronts in the middle of the shelf during winter months. With similar features as observed in other regions (e.g. Mid-Atlantic Bight), the driving mechanisms of these winter fronts have been explored. Analysis of the SST dataset combined with the results of a hydrodynamic model showed that these thermal fronts carry a salinity signature. They are shown to be a particular case of density fronts where the main driver of the density difference is the increased freshwater input over the shelf. The role of the surface cooling in winter, wind stress, and background circulation in the formation and distribution of these winter time fronts is investigated.

After describing the spatial and seasonal evolutions of frontal occurrence over the northern part of the continental shelf in the Bay of Biscay, a first insight in explaining the processes that sustain frontal activity is proposed. This step is mandatory to improve models in this region and to estimate the impact of these structures on biogeochemical activity.

Back to: The Dynamics of Buoyancy Driven Flows in Estuaries and River Plumes and on the Continental Shelf IV Posters