Potential for fresh submarine groundwater occurrence in an arid Mediterranean region: the case of Gulf of Gabes, Tunisia

Arid and semiarid zones, including the southern Mediterranean countries, are among the world’s most affected by water scarcity. Unconventional water resources, such as submarine fresh groundwater, may be key contributors to mitigate ongoing and future water crises for coastal regions and islands. In the Gulf of Gabes, Tunisia, several deep confined aquifers have been identified and the parts that are onshore have been well characterized. However, the offshore extension of these aquifers has been unexplored to date, except beneath Kerkenah and Djerba islands, where a number of exploitation wells are operating. In this work, the existing, but fragmented, geological, geophysical and hydrogeological data from both the marine and terrestrial sides of the Gulf of Gabes are synthesized for the first time in order to map the offshore extension of the deep aquifers and identify the quality of their groundwaters. Geological data confirmed the offshore continuity of the deep aquifers contained in the Miocene siliciclastic formations, particularly the Serravallian-Tortonian (ST) water-bearing horizon, on which the present research focuses more specifically, because of its wide extension and potential. In the study region, the ST aquifer is present onshore and is currently exploited in Kerkenah and Djerba islands. Offshore, the average thickness of the ST aquifer is ~200 m. Wireline log data suggest total porosity and salinity ranges of 30–36% and 5.5–7.5 g/L, respectively. These conditions make the offshore water-bearing horizon of potential interest for agriculture, industry and domestic purposes, including after adequate treatments such as desalination or dilution with freshwater.