Mechanisms of surface wave energy dissipation over a high-concentration sediment suspension
Citable URI
https://hdl.handle.net/1912/7329As published
https://doi.org/10.1002/2014JC010245DOI
10.1002/2014JC010245Keyword
Fluid mud; Wave dissipation; Laminar and turbulent wave boundary layers; Lutocline instabilities; Wave-supported turbidity flowsAbstract
Field observations from the spring of 2008 on the Louisiana shelf were used to elucidate the mechanisms of wave energy dissipation over a muddy seafloor. After a period of high discharge from the Atchafalaya River, acoustic measurements showed the presence of 20 cm thick mobile fluid-mud layers during and after wave events. While total wave energy dissipation (D) was greatest during the high energy periods, these periods had relatively low normalized attenuation rates (κ = Dissipation/Energy Flux). During declining wave-energy conditions, as the fluid-mud layer settled, the attenuation process became more efficient with high κ and low D. The transition from high D and low κ to high κ and low D was caused by a transition from turbulent to laminar flow in the fluid-mud layer as measured by a Pulse-coherent Doppler profiler. Measurements of the oscillatory boundary layer velocity profile in the fluid-mud layer during laminar flow reveal a very thick wave boundary layer with curvature filling the entire fluid-mud layer, suggesting a kinematic viscosity 2–3 orders of magnitude greater than that of clear water. This high viscosity is also consistent with a high wave-attenuation rates measured by across-shelf energy flux differences. The transition to turbulence was forced by instabilities on the lutocline, with wavelengths consistent with the dispersion relation for this two-layer system. The measurements also provide new insight into the dynamics of wave-supported turbidity flows during the transition from a laminar to turbulent fluid-mud layer.
Description
Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 120 (2015): 1638–1681, doi:10.1002/2014JC010245.
Collections
Suggested Citation
Journal of Geophysical Research: Oceans 120 (2015): 1638–1681Related items
Showing items related by title, author, creator and subject.
-
Rates and mechanisms of turbulent dissipation and mixing in the Southern Ocean : results from the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES)
Sheen, Katy L.; Brearley, J. Alexander; Naveira Garabato, Alberto C.; Smeed, David A.; Waterman, Stephanie N.; Ledwell, James R.; Meredith, Michael P.; St. Laurent, Louis C.; Thurnherr, Andreas M.; Toole, John M.; Watson, Andrew J. (John Wiley & Sons, 2013-06-04)The spatial distribution of turbulent dissipation rates and internal wavefield characteristics is analyzed across two contrasting regimes of the Antarctic Circumpolar Current (ACC), using microstructure and finestructure ... -
Estimating oceanic turbulence dissipation from seismic images
Holbrook, W. Steven; Fer, Ilker; Schmitt, Raymond W.; Lizarralde, Daniel; Klymak, Jody M.; Helfrich, L. Cody; Kubichek, Robert (American Meteorological Society, 2013-08)Seismic images of oceanic thermohaline finestructure record vertical displacements from internal waves and turbulence over large sections at unprecedented horizontal resolution. Where reflections follow isopycnals, their ... -
Dissipation processes in the Tongue of the Ocean
Hooper, James A.; Baringer, Molly O.; St. Laurent, Louis C.; Dewar, William K.; Nowacek, Douglas P. (John Wiley & Sons, 2016-05-14)The Tongue of the Ocean (TOTO) region located within the Bahamas archipelago is a relatively understudied region in terms of both its biological and physical oceanographic characteristics. A prey-field mapping cruise took ...