Submarine groundwater discharge in the southeastern Mediterranean (Israel)

Low salinities and relatively high ²²²Rn activities were found in several sites along the northern coast of Israel. Seawater salinities were as low as 37.4 ppt (compared with 39.6-39.8 ppt in eastern Mediterranean water) and ²²²Rn activities were up to 3.5 dpm/l, implying the existence of Submarine Groundwater Discharge (SGD). ²²⁶Ra activities were usually low (< 0.3  dpm / l), suggesting that the discharge is mainly of fresh water. Very high radon activities (up to 1,800 dpm/l) with strong tidal variability were found in small tidal flat springs in northwestern Carmel. High activities of ²²²Rn were not found at any site south of Mt. Carmel, and low salinities were documented just at two sites. The lack of SGD in the south is probably due to the efficient confinement of the Cretaceous carbonate aquifer and to the reduced hydraulic heads in the overlying Pleistocene granular aquifer. On the other hand, the SGD in the north is from the Cretaceous aquifer, either by direct discharge to the sea or through the overlying Pleistocene aquifer. The latter becomes possible due to the absence of confining layers or via transversal faults.