Submerged notches in Istria and the Gulf of Trieste: Results from the Geoswim project

This paper is aimed at mapping the submerged notch along the northeastern Adriatic coast and discussing the relations between the submerged notch, the seawater, the groundwater and the freshwater discharge along the coasts of the study area. Using hydrological and observational data collected during a solitary snorkel-swimming expedition along ∼250 km-long route along the Istrian coasts and thermal and topographical data, we discuss the hydrogeological and topographical constraints on the origin and development of the submerged notch in the northeastern Adriatic Sea. The submerged notch was surveyed at depths ranging between −0.6 m m.s.l. and −2.6 m m.s.l. in the northern sector of the Gulf of Trieste (Italy), and at about −0.5/−0.7 m m.s.l along the Limski channel (Croatia). Along the Savudrija peninsula, a slightly carved submerged notch was surveyed at −0.5/−0.6 m m.s.l. The modern notch is completely lacking in the study area. Topographical data highlight that the submerged notch occurs in correspondence of plunging cliffs. Moreover, the submerged notch developed in correspondence of the submarine springs that allow mixing-zone dissolution. Data suggest that the mixing-zone dissolution, caused by the freshwater from submerged springs or from the largest rivers in the Gulf of Trieste, was a major factor in developing submerged notches. These new observations provide basic data for future studies on the development of the submerged notch along the northeastern Adriatic coast, previously linked almost exclusively to bioerosion.