Seafloor evidence for the interaction between cascading and along-slope bottom water masses

The steep slope of the SW Adriatic margin (Central Mediterranean) is impacted today by two water masses having markedly different origin but a similar southward flow component: the Levantine Intermediate Water (LIW) and the North Adriatic Deep Water (NAdDW). The LIW forms through evaporation in the eastern Mediterranean and enters the Adriatic along a counterclockwise path. The NAdDW forms through winter cooling on the North Adriatic shelf and cascades across the western slope of the South Adriatic basin. Bathymetric and side-scan sonar (TOBI) images of the SW Adriatic margin, accompanied by Chirp sonar profiles, define an area of extreme seafloor complexity characterized by a variety of sediment waves, erosional scours, longitudinal furrows, and giant comet marks. These distinctive bottom-current features are not randomly distributed but appear genetically linked and have a consistent down-current arrangement. We ascribe this seafloor pattern to the constructive interference of the highly saline LIW, flowing along the slope between 200- and 600-m water depth, and the cold NAdDW, plunging off-shelf obliquely to the slope. Stratigraphic data indicate that this oceanographic regime has been active since the last glacial-interglacial transition. The cascading NAdDW is density driven but is not short-lived (as a turbidity current would be); consequently, the interaction between downslope and along-slope currents is here more dynamical as two water masses act simultaneously over a prolonged interval, somewhat diverting their paths and leading to locally enhanced energetic conditions at the seafloor