HR: 1340h
AN: OS23C-1323    [Abstracts]
TI: Sediment Resuspension and Transport During Bora in the Western Adriatic Coastal Current
AU: * Mullenbach, B L
EM: bmullenbach@ocean.tamu.edu
AF: Texas A&M University, Department of Oceanography, College Station, TX 77843-3146 United States
AU: Geyer, W R
EM: rgeyer@whoi.edu
AF: Woods Hole Oceanographic Institution, Applied Ocean Physics and Engineering, Woods Hole, MA 02543 United States
AU: Sherwood, C R
EM: csherwood@usgs.gov
AF: U.S. Geological Survey, 384 Woods Hole Road, Woods Hole, MA 02540-1598 United States
AB: The Western Adriatic Coastal Current (WACC) is an important agent for along-shelf transport of sediment and fresh water in the western Adriatic Sea. The WACC is driven by a combination of buoyancy forcing from the Po River (northern Adriatic) and wind forcing from northeasterly Bora winds. The large seasonal pulse of freshwater (during the winter) from the Po River influences WACC strength; however, preliminary results from current measurements and model runs indicate that the WACC responds quickly and strongly to Bora wind events, with a strengthening of the current moving southward. Along-margin sediment transport to the south is significantly increased as a result of Bora wind events, presumably because of enhanced wave resuspension and WACC velocity. Elevated sediment fluxes have been observed in both the upper water column (i.e., core of the WACC) and bottom boundary layer (BBL) during these events, which suggests that wind-driven currents may be coupled with the near-bottom transport. This study addresses the interaction of the WACC with the BBL and the impact of this interaction on sediment transport in the western Adriatic. Two benthic tripods were deployed from November 2002 to June 2003 on an across-shelf transect near the Chienti River (at 10 and 20-m water depth), in the region where WACC begins to intensify (200 km south of Po River). Continuous measurements of suspended sediment concentration and current velocity were recorded in the upper-water column and BBL to document sediment transport events. A time series of sediment fluxes and shear velocities (from currents only, u$_{*c}$; from waves and currents, u$_{*wc}$) were calculated from these data. Results show that suspended sediment concentrations near the seabed (few cmab) during Bora wind events are strongly correlated with u$_{*wc}$, which supports a previous hypothesis that wave resuspension (rather than direct fluvial input) is responsible for much of the suspended sediment available for transport southward of the Po River. In contrast, suspended sediment concentrations farther away from the bed (50 cmab) are highly correlated with u$_{*c}$, but not with u$_{*wc}$. These results suggest that WACC velocity during Bora events controls the ability of sediment to escape the wave boundary layer and be suspended farther away from the seabed. This implies that turbulence induced by currents, rather than waves, allows sediment to move higher in the water column and become available for transport by fast-moving currents generated by the WACC, thus producing strong southward sediment fluxes observed during Bora events. Specific mechanisms responsible for the vertical structure of suspended sediment and estimates of vertically integrated fluxes during these Bora events are yet to be established because of the difficulty in estimating suspended sediment concentrations throughout the water column from acoustic data; these issues are still under investigation and progress will be assessed.
DE: 4211 Benthic boundary layers
DE: 4219 Continental shelf processes
DE: 4558 Sediment transport
DE: 3022 Marine sediments--processes and transport
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting