  Above steep deep-sea topography internal tidal waves may break vigorously.
The associated turbulent mixing is important for resuspending matter, bringing
it tens of meters away from the seafloor for redistribution. While intense
turbulence-generation occurs around a primary (frontal) bore during each
transition from warming downslope to cooling upslope phase of the internal
(tidal) carrier wave, a secondary bore can appear about half a wave-period
later before the turn to the warming phase. As will be demonstrated from a
100-day mooring array consisting of 200 high-resolution temperature sensors
between h = 6-404 m above a steep slope of a large North-Atlantic seamount and
a low-resolution acoustic Doppler current profiler sampling between 50 and 450
m, secondary bores show about the same turbulence intensity as around primary
bores but they generally show larger overturns that always reach the seafloor.
The secondary bores associate with a sudden drop in along-isobath flow speed, a
(renewed) increase in upslope flow of up to |0.2| m s-1, and with
first-harmonic quarter-diurnal periodicity which provides a spectral peak for
turbulence dissipation rate. While each bore is different in appearance,
varying from curved like a primary bore to almost straight upward with a ragged
bore, secondary bores are in a first approximation forward breaking in contrast
with backward breaking primary bores.
