Geology Reference
In-Depth Information
Fig. 14.5
(
a
) Current velocities and orientations from Horizon
Guyot, Pacifi c Ocean, in 1,700 m water depth. Notice that the
orientation of the current shifts progressively during the change
in the tidal current. This progressive change seems to be typical
of unconfi ned internal tidal settings, as opposed to confi ned set-
tings (e.g. within submarine canyons) where the change is often
abrupt (Modifi ed from Lonsdale et al.
1972
) . (
b
) Current velocities
showing a well-defi ned semi-diurnal reversal of direction for
Horizon Guyot, Pacifi c Ocean (Modifi ed from Cacchione et al.
1988
) . (
c
) Residual vectors for (
b
), showing consistent changes
in the orientation of the total current direction over long time
scales
the internal tide, modifi ed by the Coriolis effect,
similar to amphidromic systems in surface tides
(Fig.
14.5a
) (Kvale
2006
). Changes in the orientation
of internal-tide related currents has also been shown
to occur on a longer time-scale in the open ocean,
although the cause is again not well understood
(Fig.
14.5b, c
) (Cacchione et al.
1988
; Noble et al.
1988
). A few current measurements within deeply
incised submarine canyons also show occasional
cross-canyon current directions, however, these do
not generally correlate to either a tidal period or the
tidal cycle, suggesting they are either contour cur-
rents or internal waves spun-off from internal tidal
waves (Rudnick et al.
2003
), or are generated by
another mechanism altogether, such as surface wind
shear (Shepard et al.
1979
) .
