Abyssal Current Character Determined from Sediment Bedforms on the Nova Scotian Continental Rise

摘要

Bottom photographs across the Nova Scotian continental rise show effects of an intense bottom current at 4800-5000 m that decreases in strength upslope to tranquil near-bottom conditions at 3200-4000 m. Apparently weak currents are present above 3200 m. Long-term, geologically significant flow parallels the bathymetric contours toward the southwest, but significant short-term variability in direction is indicated by orientations of small-scale bedforms. The Western Boundary Undercurrent, documented elsewhere along the continental margin at depths less than 4000 m, has relatively little effect in modifying the sea floor on the Nova Scotian rise, but the deep currents (>4000 m) have a significant effect. Repeated photography of small seafloor areas suggests that many bedforms, especially those of smaller scale, are constructed and destroyed by strong, variably directed, current events (benthic storms) on time scales of 3-6 months or less. Thus, a significant part of the geologic response of the seabed to currents may be event-controlled on time scales not very different from those in coastal environments.