A snapshot of the circulation and hydrology of the southern and central shelf regions of the Benguela Current in winter 1999 : BENEFIT Marine Science
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Currents and hydrological parameters were measured on the shelf
regions of the southern and central Benguela Current system in
June (winter) 1999, using a vessel-mounted acoustic Doppler
current profiler (ADCP) with differential GPS input, which operated
continuously, and CTD casts at selected stations. Three lines
extended to the shelf break, off Saldanha Bay / Cape Columbine,
the Orange River mouth, and Walvis Bay. Results concerning
near-surface circulation patterns (at 30-40 m depth) corroborate
previous findings. Northward to northwestward flow was recorded
on the outer shelf and southward flow inshore, from Saldanha Bay
to theOrange River Bank, where time-dependent inertial flows were
found in the upper as well as in the lower layers. Currents north of
28°S were much weaker, with offshore flow occurring within the
upwelling centre north of Luderitz and onshore flow just south of
Walvis Bay, in keeping with previous studies and a composite
sea-surface temperature satellite image for the cruise period.
OppositeWalvis Bay, near-surface northward flow was reduced to a
weak narrow band in the mid-shelf region. An analysis of over a
thousand 5-minute ADCP time averages of current speed along the
ship's track from 34 to 23 o S (all directions, at a nominal 34mdepth,
on the shelf inside the 200-m isobath) showed a mean speed of
20.0 cmslsupg-1l/supg (s.e. 0.3 cm s -1 ) south of 28 o S and 10.7 + 0.5 cmslsupg-1l/supg north
of that latitude, the difference being highly significant.