Benguela - Pta Palmeirinhas
Figure 3 show the distribution of surface temperature observed with the thermograph at 4 ml of depth and the distribution of temperature, salinity and oxygen in the profiles. The surface temperature distribution is characterized by a gradual increase northwards from about 24°C south of Benguela to about 29°C off Cabo Ledo. Colder water is observed close to the shore and there is an increase of temperature oceanwards. Two sections were worked in the region, off Lobito and Palmeirinhas respectively. The vertical distribution of variables does not differ very much from that found at about the same time during previous cruises. In both sections there is a strong thermocline well demonstrated at 25 - 50 m depth followed by a gradual decrease of temperature towards deeper layers. A characteristic of the section off Palmeirinhas is the low salinity content of the surface waters, advected from the Congo river runoff by the southward flowing Angola current. This effect is not seen off Lobito where two cores of high salinity are observed, in surface and subsurface. That in subsurface of about 35.80 ‰ is probably advected from much lower latitudes as it is also well visible off Palmeirinhas between 50 and 75 m. The oxygen content over the shelf is relatively high, presenting values which are not likely to limit the distribution of the fish here.
Pta. Palmeirinhas - Cabinda
Figure 4 shows the distribution of surface temperature observed with the thermograph at 4 m depth and the distribution of temperature, salinity and oxygen in the profiles. Colder water is observed close to the shore and there is an increase of temperature offshore. Two sections were worked in this region, off Lobito and Palmeirinhas and two more further north, in Ponta da Moita Seca and off Cabinda. The vertical distribution of variables does not differ very much from that found at the same season during previous cruises. However, the profiles off Cabinda and P. Moita Seca showed a very shallow thermocline at about 10 m, a thin layer of low salinity and a sharp halocline, coinciding also with the thermocline. In the south the thermocline lies at about 25 - 50 m, followed by a gradual decrease of temperature towards deeper layers. The two cores of low salinity observed in Palmeirinhas indicate two different flows. The low saline water close to the shore originates from the Kwanza river discharge, situated south of the section, and advected northwards by a coastal current. Further offshore the low salinity observed is from the Congo and this water is advected by the southward flowing Angola current. In all the sections there is a maximum of salinity at about 50 - 75 m probably transported into the region from much lower latitudes. In the horizontal surface salinity distribution charts off the Congo mouth, low saline waters can be traced in a northern direction, joining the Congo current, and oceanwards joining the south turning waters of the Angola current. This all confirm the general pattern of surface circulation at this time of the year.
The oxygen content over the shelf is relatively high, presenting values which are not likely to limit the distribution pattern of the fish there.
