The Rhone river dilution zone present in the northeastern shelf of the Gulf of Lion in December 2003

Acoustic doppler current profiler (ADCP), CTD and thermosalinograph data from the Gulf Of Lion Time Series (GOLTS) cruise of December 2003, and corresponding AVHRR images, show the unusual presence of the Rhone river dilution zone far east from the Rhone river mouth. It is the first time this event is studied with simultaneous hydrological and current data. This dilution zone extends as far as 5.27°E in longitude (45 km from the Rhone river mouth). At longitude 5.13°E (37 km from the Rhone river mouth), the dilution zone is 40 m deep and spreads over 0.075° latitude (8 km). It is due to an eastward current present there throughout the ADCP-detected range (12–120 m). The analysis of moored ADCP time series reveals that such eastward currents occur there about 18% of the time and that diluted waters from the Rhone reach the Station d’Observation Fixe (SOFI) site between 3.9% and 8.4% of the time. This December 2003 event is the consequence of the combined effects of a storm with east winds and the presence of freshwater along the coast.