PARTICLE TRANSPORT AND ACCUMULATION IN NORFOLK AND BALTIMORE CANYONS

The Mid-Atlantic Bight is incised by several large canyons two of which were studied as part of a multi-disciplinary project initiated by the Bureau of Ocean Energy Management (BOEM, USA) and jointly funded by BOEM, NOAA and USGS. The heads of the canyons, which are situated 140 km apart, both lie at a distance of 90 km off shore on the same shelf margin and lack direct input from rivers. Two hypotheses were formulated at the start of the study: i) canyons incising the MAB shelf, including Norfolk and Baltimore, capture sediment and organic carbon. This transport ultimately enriches the canyon floor sediment, resulting in higher concentration and quality of carbon than the adjacent slope, and ii) given Baltimore and Norfolk canyons have a very different morphology and orientation from each other, and previous reports indicated differences in sediment grain size and transport properties, the canyons have different sedimentation patterns and accumulation rates, which explains the differing faunal communities between the two canyons. Core samples collected along the canyon axis and for comparison on the adjacent open slope were analyzed for their sediment composition, organic matter content and accumulation rates. Additionally water column properties, including turbidity were measured with CTD. In contrast to our expectations, sediment distribution, sedimentation rates and organic matter content differed strongly between both canyons. Although accumulation rates in both canyons were higher than accumulation rates on the open slope, Norfolk canyon showed an even distribution of sediment and organic matter along the canyon axis. While two distinct zones were observed in Baltimore Canyon; coarse grained sediments with low organic matter in the upper canyon and finer grained sediments with high organic matter content in the lower canyon. Differences are attributed to canyon morphology, physical processes and active particle transport.