Currents and sediment transport in the Mississippi Canyon and effects of Hurricane Georges |
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| Authors: | Cheryl Burden Ross Wilford D Gardner Mary Jo Richardson Vernon L Asper |
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| Institution: | 1. MIT/WHOI Joint Program in Oceanography/Applied Ocean Science and Engineering, Woods Hole, MA, USA;2. Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, USA;3. Department of Ocean Sciences, University of California Santa Cruz, Santa Cruz, CA, USA;4. Bigelow Laboratory for Ocean Sciences, East Boothbay, ME, USA;5. Gradient, 20 University Road, Cambridge, MA, USA;6. School of Ocean and Earth Sciences, National Oceanography Centre, University of Southampton, Southampton, UK;1. Department of Oceanography and Coastal Sciences, Coastal Studies Institute, School of the Coast and Environment, Louisiana State University, United States;2. Department of Fisheries Oceanography, The School of Marine Science & Technology, University of Massachusetts-Dartmouth, New Bedford, MA 02744, United States;3. International Center for Marine Studies, Shanghai Ocean University, Shanghai 201306, China;1. Ministry of Education Key Laboratory for Coast and Island Development, Nanjing University, Nanjing 210093, China;2. Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China;1. Maritime Engineering Laboratory at Polytechnic University of Catalonia (LIM/UPC), c./Escar, 6, 08039 Barcelona, Spain;2. Maritime Engineering Laboratory at Polytechnic University of Catalonia (LIM/UPC) and International Centre of Coastal Resources Research (CIIRC), c./Jordi Girona, 1-3, 08034 Barcelona, Spain |
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| Abstract: | The temporal variability in currents, temperature, and particulate matter concentration were measured in the Mississippi Canyon axis where the thalweg was 300 m deep from May–July and August–November 1998 using current meters, thermographs, a light-scattering sensor, and sediment traps. Canyon sediments were sampled by coring and observed using an ROV video camera. Currents in the upper Mississippi Canyon generally oscillated up/down canyon with diurnal periodicity and were bottom-intensified. Mean current speed at 3.5 mab was approximately 8 cm s?1 during both deployments, reaching maximum speeds of over 50 cm s?1 under normal conditions. Based on current velocities, critical bed shear stress for resuspension of canyon-floor sediments was exceeded about 30% of the time during both deployments. In late September, Hurricane Georges passed 150 km NE of the study site, significantly intensifying current velocities, bed shear stress, resuspension, trap fluxes and temperature fluctuations. As the hurricane passed, maximum current speed reached 68 cm?s and temperature decreased ～7 °C in less than two hours. Critical bed shear stress for sediment resuspension was exceeded approximately 50% of the time during the five days of hurricane influence. Further evidence for sediment resuspension was the five-fold (and perhaps 70–130 fold) increase in trap fluxes and compositional similarities between canyon surface sediment and material collected by traps. |
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