The reshaping of the South West Adriatic Margin by cascading of dense shelf waters

The South West Adriatic Margin (SAM) includes a steep and morphologically complex continental slope stretching about 600 km from the Pelagosa sill to the Otranto strait. The margin is clearly dissected by submarine slides, active fault systems (e.g.: the Gondola deformation belt), numerous shallowly incised and relatively straight canyons located south of Bari Canyon, and a variety of large-scale erosional and depositional features. This area is seasonally impacted by dense shelf water forming in the North Adriatic through wind-forced winter cooling, moving south along the western side of the basin, and cascading across the South Adriatic slope.The area has been investigated through multibeam surveys integrated by high-resolution seismic stratigraphic data resolving glacial and post-glacial deposits. This paper gives a detailed and comprehensive description of the SAM seafloor morphology to document how the process of dense shelf water cascading concurs to a thorough "restyling" of the submarine landscape by interacting with the pre-existing and markedly differentiated morphologies and sediment distribution. We focus on depositional and erosional features such as: giant sediment drifts down to 1200 m water depth, muddy and sandy sediment waves, comet marks against pre-existing slide blocks, furrow fields against steep slopes, large scours at the shelf edge and large erosional moats adjacent to major morphological barriers. The analysis of the bedform orientation and spatial distribution indicates that the downslope-cascading bottom-currents (dominantly directed to the SE) encounter a straight upper slope, oriented north south in the north and progressively more east west proceeding to the south; as the slope orientation becomes more E-W it also appears more dissected by small-scale canyons, active during glacial times. In the latter area, therefore, the dense shelf waters follow a slope-parallel direction almost perpendicular to the pre-existing slope canyons. As a consequence, erosional furrows develop perpendicular to the canyon flanks and some of the canyon heads become disconnected from the main canyon downslope.