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Along with the
large scale mean features, there is a lot of high-frequency variability in
the data. This is a plot showing depth and time dependence of the
east-component of velocity and shear magnitude from the Gould winter
cruise, LMG-0106 (Process Site #3). Interpretation of the variability is
really only possible when the vessel is stationary or only slowly moving for
a significant time interval. In general, this only occurs during the Gould
process sites.
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In this example,
we see a strong semidiurnal oscillation. From checking its period, we can see
that this oscillation is clearly inertial (period ~13 h), not tidal (periods
of ~12.42 h and 12.00 h). The currents are up to 30 cm/s in the surface mixed
layer, and weaker but still significant in the lower layer (stratification is
shown in the left-hand panels). From
a moving platform like the Palmer survey cruises, oscillations this
strong will mask all but the strongest mean flows.
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The high shear
across the pycnocline near 110 m suggests to us that there is a potential for
mixing to occur through the onset of dynamical instabilities. We look at this in the next slides.
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