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

Abstract

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.