Sediment transport processes from the topset to the foreset of a crenulated clinoform (Adriatic Sea)

Crenulated clinoforms of complex and uncertain origin characterize large portions of the Late-Holocene prograding mud wedge in the western Adriatic continental shelf. Sediment failure was originally postulated as the most plausible mechanism for the formation of the crenulations. Subsequent work has shown that, although the origin of the crenulations may have been related to deformation processes, their maintenance through time seems to be better explained by different sediment accumulation rates in the flat and steep flanks. In order to establish relationships between active sediment dynamics, across-shelf transport and sediment accumulation in these crenulated clinoforms, two tripods and a mooring were deployed off the Pescara River during autumn and winter 2002–2003 as part of the EuroSTRATAFORM program, and in combination with the Po and Apennine Sediment Transport and Accumulation (PASTA) study. The tripods were placed on the shallow topset region and close to the clinoform roll-over point (i.e., offlap break), at 12 and 20-m water depth, respectively, and the mooring was located at 50-m depth, in the crenulated foreset region. Several sediment-resuspension events were recorded, mainly related to Bora and Sirocco storms, during which wave–orbital and current velocities increased considerably. Sediment transport in the topset region was predominantly towards the SE, following the direction of the coastal current and the bathymetry, but showing a significant offshore component at the roll-over point that was intensified during storm events. Currents at the foreset region were also directed to the SE. In mid-waters they were clearly aligned with the local bathymetry, whereas near the bottom they had an important and persistent offshore component. This current behavior seems to be associated with an intense bottom Ekman transport that causes the near-bottom current to be deflected to the left (i.e., offshore) with respect to the direction of the surface current. This mechanism enhances the suspended-sediment transport from the topset down the foreset region along the Adriatic prograding mud wedge, contributing to the basinward clinoform progradation and controlling the depth of the clinoform roll-over point. In addition, activity of near-inertial internal waves was also recorded by the near-bottom instrument deployed in the foreset region. During periods characterized by a strong near-inertial signal, increases of the water turbidity clearly coincided with an intensified offshore velocity component, which suggest that this mechanism also contributes to the transport of suspended sediment across the clinoform. Both the bottom Ekman transport and the internal waves are mechanisms that could be responsible for the formation/maintenance of the Adriatic seafloor crenulations until present-day, although several arguments suggest that the latter likely plays the major role.