Hydrodynamics over the Gulf of Valencia continental slope and their role in sediment transport

Circulation patterns and sediment dynamics were studied over the Gulf of Valencia (GoV) continental slope during spring and winter 2011-2012. Two moorings were deployed at two locations; at 450 m depth from February to May 2011, and at 572 m depth from October 2011 to February 2012. At both mooring sites, observations were made of currents, temperature and near-bottom turbidity within the lowermost 80 m above the seafloor. The temperature measurements allowed distinction of the different water masses and their temporal evolution. The fluctuations of the boundary between the Western Mediterranean Deep Water (WMDW) and the Levantine Intermediate Water (LIW) masses were monitored, and several intrusions of Western Mediterranean Intermediate Water (WIW) were observed, generally coinciding with changes in current direction. At both mooring sites, the currents generally maintained low velocities <10 cm s−1, with several pulses of magnitude increases >20 cm s−1, and few reaching up to 35 cm s−1, associated with mesoscale eddies and topographic waves. The current direction was mainly towards the SSE on the first deployment and to the ESE on the second deployment. This second location was affected by a strong bottom offshore veering presumably generated by local topographic effects. Increases in suspended sediment concentrations (SSC) were observed repeatedly throughout the records, reaching values >3 mg l−1. However, these SSC variations were uncorrelated with changes in velocity magnitude and direction and/or with temperature oscillations. Results presented in this paper highlight the complex relation between the hydrodynamics and sediment transport over the GoV continental slope, and suggest that other potential sediment resuspension mechanism not linked with current fluctuations, might play a key role in the present-day sedimentary dynamics. Resuspension due to bottom trawling appears to be the most plausible mechanism.