A snapshot of the circulation and hydrology of the southern and central shelf regions of the Benguela Current in winter 1999 : BENEFIT Marine Science

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.