VIABLE DIATOMS AND CHLOROPHYLL-A IN CONTINENTAL-SLOPE SEDIMENTS OFF CAPE-HATTERAS, NORTH-CAROLINA

Continental slope sediments off Cape Hatteras, North Carolina, were sa mpled by box coring in late summer, 1992. The chlorophyll a concentrat ions measured in sediments from 16 sites at depths ranging from 530 to 2003 m averaged 19.9 mg chi a m(-2), a concentration much higher than observed elsewhere on the eastern U.S. continental slope, indicating high depositional rates for microalgal material. The variability in th e chlorophyll a values suggests strong environmental heterogeneity at both small and large spatial scales in this slope habitat, probably a consequence of both topography and bioturbation. Viable diatoms were f ound in sediment samples across the range of depths sampled, and up to 14 cm deep in sediments, indicating high rates of deposition and biot urbation. Bulk sediment samples contained planktonic, tychopelagic and benthic diatoms, indicating that both phytoplankton and benthic micro algae from the continental shelf may be sources of organic matter for these slope sediments.