North-Atlantic Oscillation and regional-scale sea-surge variability in Gulf of Lions during the 20th century

Article soumisInternational audienceSea-surge variations recorded at three tide-gauge stations (Grau-de-la-Dent, Sète, and Port-Vendres) around the Gulf of Lions (Northwest Mediterranean Sea) are mostly locally forced by onshore winds blowing from 90° to 180° related to an atmospheric depression usually centered between the Bay of Biscay and the British Island, which is more prevalent during the negative phase of the North-Atlantic Oscillation (NAO). During the second half of the 20th century, the long-term increase of sea-surge height at Grau-de-la-Dent finds no counterpart in the positive deviation of the NAO. The relationship between the monthly frequency of sea surges > 20 cm at Grau-de-la-Dent and the monthly mean NAO Index significantly strengthens from 1975. This is synchronous with the eastward shift of the two main centers of the NAO (i.e. Iceland low and Azores high) and an increase of the occurrence of depressions near the Bay of Biscay and of surge-related onshore winds in the Gulf of Lions during negative phases of the NAO