Field observations of bed shear stress and sediment resuspension on continental shelves,Alaska and California |
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| Affiliation: | 1. U.S. Geological Survey, Menlo Park, CA 94025, U.S.A.;1. Royal Netherlands Institute for Sea Research, NIOZ, Texel, The Netherlands;2. Helmholtz Centre for Ocean Research, GEOMAR, Kiel, Germany;3. University of California, Santa Barbara, USA;4. Bubbleology Research International, USA;1. University of A Coruña, Laboratorio de Ingeniería Mecánica, 15403 Ferrol, Spain;2. Ifremer, BP 70, 29280 Plouzané, France;1. The Key Laboratory of Aquatic Biodiversity and Conservation of Chinese Academy of Sciences, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China;2. University of Chinese Academy of Sciences, Beijing 100039, China;3. Institute of Deep-sea Science and Engineering, Chinese Academy of Sciences, Sanya 572000, China;1. Department of Psychology, Cognitive and Developmental Psychology, University of Zurich, Switzerland;2. Max Planck Institute for Evolutionary Anthropology, Developmental and Comparative Psychology, Leipzig, Germany;3. Anthropological Institute & Museum, University of Zurich, Switzerland;4. School of Psychology & Neuroscience, St Andrews, United Kingdom |
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| Abstract: | Bed shear stress was estimated using wave and current measurements obtained with the GEOPROBE bottom-tripod system during resuspension events in Norton Sound, Alaska, and on the northern California shelf. The boundary-layer model ofGrant andMadsen (1979, Journal of Geophysical Research,84, 1797–1808) was used to compute the bed shear stress under combined wave-generated and quasi-steady currents. Resuspension events were identified by sudden, large increases in light scattering at 1.9 m above the sea floor. The shear-stress values were used to compute the Shields parameter (ψ). The results for Norton Sound are in excellent agreement with the Shields threshold criterion; the data for the California shelf plot somewhat above the Shields threshold curve, though generally within the scatter envelope. Although the surface sediments in each area contain substantial fine-grained fractions (mean diameters were 0.007 cm in Norton Sound and 0.002 cm on the California shelf), the results do not indicate significant cohesion, because the sediment was entrained at bed shear-stress values close to those predicted by the modified Shields curve for cohesionless fine-grained particles. We suspect that frequent wave stirring and observed plowing of the surface sediment by benthonic animals maintain a high water content and contribute to the ease with which these materials are resuspended. |
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