The positions of the hydrographic sections are shown in Figures 1 - 4 and the distribution of temperature, salinity and oxygen in Figures 5 and 6. The surface temperatures range from 15°C to 23°C, which is some 5-8°C lower than found in February, demonstrating the change from a summer to a winter situation. The thermocline in 30-50 m depth is now less developed. The distribution of temperature and oxygen towards the coast demonstrate that active upwelling was taking place at least as far north as Pta das Palmeirinhas. The section off Cabinda demonstrate the same northward flow of low-salinity surface water originating from the Congo as demonstrated in the second surveys.
When calling on Luanda on August 24 we were informed that large areas of discoloured surface water (brownish) had been observed off that part of the coast, Spanish shrimp trawlers had also made such observations. Under the survey north of Luanda we observed several areas of strongly coloured surface water of brownish milky apparance. One of these areas off Ambrizete coincided with a dense distribution of surface schooling sardinella. Bioluminisence was prominent at night. A sample analysed at the Institute of Marine Research, Bergen showed a content of some dead organic material, fecal pellets, detritus, but the main part derived from living organisms, both phyto- and zooplankton. The dominating plant component was an autotrofic dinoflagellate Prorocentrum micous, but some large diatoms were also found, e.g. Rhizosolenia alata, Nitzschia longissima and several unidentified Nitzschia species. Among the zooplankton a free living unidentified nematode abt 0.5 mm dominated. The shells of several Tintinid species were found, e.g. Farella sp. Some heterotrofic dinoflagellates such as Prorocentrum sp. and Noctiluca sp. were also found.
The discoloured water thus probably resulted from unusually heavy primary and secondary production perhaps originating from areas of intensive upwelling.
The seasonal shift to a winter climate should according to literature be accompanied by a northward faunistic displacement. The findings of Survey III confirm that a northward movement of pelagic fish had taken place, particularly for sardines and sardinellas.
