Two areas of the west Florida shelf seafloor were
studied in order to understand the spatial and temporal
variations in sedimentary cover, the relationship
between sedimentary properties and remotely sensed
data, and the relationships of data of different spatial
and temporal scales. Analyses of side-scan sonar
imagery, sediment samples, and box cores reveal
spatial differences in the size, shape, spacing, surficial
grain size distribution, and sub-surface sedimentary
structures of sand ridges found at 5-8 m water depth
compared to sand lenses at 15-18 m water depth.
Northwest-southeast trending sand ridges in the
nearshore area are an order of magnitude smaller in
spatial extent than those in the midshelf. Side-scan
backscatter reflects the heterogeneity of the nearshore
surface sediments and the homogeneity of the
midshelf sediments. Box core peels reveal these
surficial sedimentary properties extend to a depth of 25
cm in both study areas.

Time series of side-scan images reveal significant but
inconsistent movement of sediments along the sharp
borders between coarse trough sediments and fine
sand features. The overall size and shape of the
first-order sedimentary features in both areas change
little over annual temporal scales. Significant
movement was also not evident during a one week
experiment related to the passage of a storm front.
Mean bottom current velocities were not sufficient to
initiate sediment movement, indicating that other
hydrologic forcing mechanisms are responsible for the
sedimentary movement observed. Shallow
sub-surface sedimentary structures in the nearshore
area indicate past sedimentary transport events related
to wave forcing and combined flow.

The results of this study show that sediment
distribution and seabed morphology vary spatially over
scales of 10’s of kilometers, but do not vary temporally
over event related or annual time scales. Hydrologic
forcing mechanisms measured here do not account for
the patterns of sedimentary morphology observed.
Backscatter correlates strongly with grain size and
carbonate content; however, modeling the relationship
between side-scan backscatter and sedimentary
properties using multiple regression analysis was not
effective. Other sedimentary and environmental factors,
such as roughness and water column properties,
significantly influence the side-scan backscatter
intensity.