Freshwater from the Bay of Biscay shelves in 2009

In April–November 2009, surface salinity data provide a good coverage of most of the south-east Bay of Biscay and nearby Aquitaine/Armorican shelves. By late April most of the shelf, in particular south of 46°N, is covered by a fresh surface layer amounting to a fresh water volume of 49 · 109 m3. At that time, a moderate amount of fresh water has spread over the Landes Plateau. By mid-June, this shelf water penetrates over the Cape Ferret Canyon north of the Landes Plateau. By mid-July, it is found west of the Landes Plateau to at least 4°W, with an estimated fresh-water content of 11–14 · 109 m3. Drifters deployed on June 17 in the Cape Ferret Canyon, or later on the shelves, confirm the spreading of shelf fresh-water over the deep ocean. Lagrangian tracking using altimetric products, also confirms the transport by a quasi-stationary circulation. Operational numerical simulations (PREVIMER, IBI, HYCOM) display this spread of the freshwater, but in different areas. In particular, all have some fresh water escaping westward near the coast in the Basque region, which is not observed. Later in the summer season, the fresh water spreads westward to south-westward and along the shelf break to at least 5.5°W in late September.