Watershed and origin of the salinity of the karstic submarine spring of Port-Miou

Watershed and origin of the salinity of the karstic submarine spring of Port-Miou (Marseille-Cassis-Bouches-du-Rhone). The salinity of the karstic submarine spring of Port-Miou has sometimes been attributed to the leaching of continental evaporites. Our recent chemical and isotopic analyses indicate a simple mixing between fresh karstic water and seawater. In the main gallery, the contamination by seawater, still present up to 2.2 km from the entrance at a depth of 147 m below the sea level, forces us to think about a general geometry that allows mixing of waters, at a great depth, in the karstic system. The measurements of the discharge of the spring indicate an excess of water compared with its supposed watershed, whereas a succinct evaluation of the aquifers of the Lower Provence indicates a deficit of discharge. Consequently, it seems possible that parts of the calcareous areas of the Lower Provence feed the springs of Port-Miou with a total catchment area of 1200 km(2). This deep and large karstic system was probably installed during the Messinian period, when the important lowering of the level of the Mediterranean Sea provoked an important gradient between Provence and the seashore. (C) 2004 Academie des sciences. Publie par Elsevier SAS. Tons droits reserves.