Impact of dense bottom water on a continental shelf: An example from the SW Adriatic margin

Abstract

Dense shelf waters have been recognised as a key factor in transporting sediment and organic matter across continental slopes; however, the effect of their circulation on continental shelves is still overlooked. The Adriatic Sea is one of the areas in the Mediterranean where dense shelf water forms and flows as a bottom-hugging gravity current along the continental margin. A fraction of this dense water passes beyond the shelf break and flows downslope through cascading, while a large (lighter and faster) portion remains on the shelf, with a principal vein flowing between 80 and 120 m water depth.This paper presents the 3D shape, internal architecture and sediment facies of a variety of large-scale sedimentary features detected on the continental shelf and at the shelf edge, between 50 and 300 m water depth. These features include giant comet marks, large flute-shaped scours, muddy sediment waves, very large dunes with superimposed bedforms, active and relict sand ridges and shelf edge contourites. Both erosional and depositional features show an overall internal geometry and orientation consistent with water masses flowing southward, and are located where flows become accelerated by topographic constraints and deviated by the curvature of the shelf edge.In this study, the morphology and seismic stratigraphic structure of large-scale bedforms are investigated in an effort to place constraints on bedform evolution and preservation, especially as predictive tools for sand resource management, and to bring new evidence of the interaction between unidirectional hydrodynamic processes and seafloor dynamics on the shelf.