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- Title
Behavior and mixing of a cold intermediate layer near a sloping boundary.
- Authors
Cyr, Frédéric; Bourgault, Daniel; Galbraith, Peter
- Abstract
As in many other subarctic basins, a cold intermediate layer (CIL) is found during ice-free months in the Lower St. Lawrence Estuary (LSLE), Canada. This study examines the behavior of the CIL above the sloping bottom using a high-resolution mooring deployed on the northern side of the estuary. Observations show successive swashes/backwashes of the CIL on the slope at a semi-diurnal frequency. It is shown that these upslope and downslope motions are likely caused by internal tides generated at the nearby channel head sill. Quantification of mixing from 322 turbulence casts reveals that in the bottom 10 m of the water column, the time-average dissipation rate of turbulent kinetic energy is 휖 = 1.6×10Wkg, an order of magnitude greater than found in the interior of the basin, far from boundaries. Near-bottom dissipation during the flood phase of the M tide cycle (upslope flow) is about four times greater than during the ebb phase (downslope flow). Bottom shear stress, shear instabilities, and internal wave scattering are considered as potential boundary mixing mechanisms near the seabed. In the interior of the water column, far from the bottom, increasing dissipation rates are observed with both increasing stratification and shear, which suggests some control of the dissipation by the internal wave field. However, poor fits with a parametrization for large-scale wave-wave interactions suggests that the mixing is partly driven by more complex non-linear and/or smaller scale waves.
- Subjects
SUBARCTIC region; DEEP-sea moorings; SCIENTIFIC observation; TIDES; SHEARING force
- Publication
Ocean Dynamics, 2015, Vol 65, Issue 3, p357
- ISSN
1616-7341
- Publication type
Article
- DOI
10.1007/s10236-014-0799-1