BIOGENIC SEDIMENTS ASSOCIATED WITH TWO HARD GROUND AREAS ALONG THE CHARLESTON TRANSECT

In November, 2006, sediment grab samples were collected using a Smith-MacIntyre grab sampler on the continental shelf off Charleston, SC, aboard the NOAA Ship Nancy Foster. Two areas located on the mid-shelf and shelf-edge were studied, both of which included hardground features (rocky exposures) surrounded by sand megaripples. The mid-shelf area (water depths of 20-25 m) is the site of the Transect River Channel, an apparent meandering river channel etched into the underlying hardground. The shelf-edge site is Doc's Rocks, a rocky outcrop of ledges in 50 m of water. Both of these areas were discovered during the College of Charleston's Transect Program in 2004 and both are potentially important areas of high benthic diversity and fish habitat. Previous work in these areas included analysis of many sediment samples from across the continental shelf, collected at depths from 10 to 100 m. These studies showed that sediments across the shelf to depths of 50 m consist primarily of medium to fine sands, and 90% of the sediment is lithogenic. Samples collected in 2006 will supplement previous collections to further examine the sediment characteristics surrounding these hardground areas. Compositional analysis will include classification of biogenic material in the size fraction greater than 500 microns. The sedimentological comparisions within and between these hardground sites will be used to add to the growing body of information to further characterize these important seafloor habitats.