Six current meter moorings were deployed from February 1991 through March
1992 along two across-shore transects over the continental shelf and slope
near the Farallon Islands, CA. One line had four moorings (A-D) between
100 and 1400 m depth, and the second line, 28 km to the north, had two moorings
(F and E) at 400 and 2000 m depth. All the moorings had a variety of instruments
spaced from 75 m below the surface to 15 m off the bottom. The goal of the
program was to study the circulation patterns over the slope and their influence
on the dispersal of dredged materials disposed of at proposed sites on the
shelf and slope. The mean currents flowed northwestward along the slope,
with the strongest currents found above 400 m. The spatial pattern of the
subtidal flow field reflected the pattern of the mean currents. These oscillatory
currents also flowed primarily parallel to the alongslope isobaths. Again,
the strongest currents (with speeds in excess of 20 cm/s) were observed
above 400 m in water depths between 400 and 1400 m. About 40% of the entire
variability in the subtidal current field moved together in this well-defined
spatial pattern. Subtidal currents measured deeper in the water column were
weaker and showed temporal patterns that were more characteristic of a specific
measurement site. Most of the variability in the subtidal current field
had fluctuations with periods larger than 10 days. The annual fluctuation
was particularly prominent. The strongest poleward flows were observed from
March through August. Subsequently, the speed of the dominant flow pattern
decreased in amplitude and became more restricted in its spatial extent.
We assume that the flow dynamics for this portion of the current field was
controlled by and is representative of the dynamics associated with the
California Undercurrent. The wind does not directly affect the slope currents
on these long time scales, for the wind is not correlated with the current
field. However, on shorter timescales, periods of 3 to 8 days, the wind
does drive currents over the slope down to depths of 200 m.
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