期刊名称：Tellus A: Dynamic Meteorology and Oceanography
电子版ISSN：1600-0870
出版年度：2019
卷号：71
期号：1
页码：1-11
DOI：10.1080/16000870.2019.1653137
摘要：Internal wave breaking upon sloping seafloors is a potential source of turbulent mixing in the deep-ocean,
but we lack details on off-bottom breaking. Turbulence processes are relevant for the dispersal away from
the seafloor of suspended materials like those emanating from thermal vents and artificial mining activities.
For the present study, high-resolution temperature sensors have been moored up to 406 m above a slope of a
2000 m deep crest of the Mid-Atlantic Ridge. In addition to familiar observations of on-slope propagating
highly nonlinear bores dominating turbulent mixing near and in contact with a sloping seafloor, the present
observations show occasionally larger than 100 m tall turbulence expansions between 100 and 250 m above
the seafloor at the transition from on- to off-slope flow. The details of such turbulence expansion are
reminiscent of an asymmetric quasi-mode-2 internal hydraulic jump, with some specific differences compared
with near-surface hydraulic jumps. As the expansion is generated at the transition from weak to steep edge of
a saw-tooth internal tidal wave, it leads turbulence and stratification in two directions: One down to the
seafloor in the direction of tidal phase propagation; the other more horizontally and slightly upward
associated with near-homogeneous overturning remaining well away from the seafloor while preceding and
sharpening near-bottom frontal bores. The mean turbulence dissipation rates O(108
–107 m2
s
3
) associated
with these expansions are half an order of magnitude less than those of on-slope propagating near-bottom
bores, while about equal in duration. As for bores, their appearance, intensity and timing vary every
tidal cycle.
