Colombia
Figure 4 shows the surface temperature measured at 4m depth by the vessels thermograph, and Figure 5, a and b, shows the profiles of the two hydrographical sections worked out, in Tumaco Bay and in the Gulf of Cupica respectively.
As shown in Figure 4, the surface waters seem quite uniform, with no latitudinal gradient and only a minor positive gradient towards the shore at two locations. The surface water on the whole shelf falls between 28 and 30° C. The hydrographic sections seem to present similar uniform conditions, with no sign of upwelling occurrence in the area covered. The oxygen deficiency zone, which can be defined as water of oxygen content less than 1 ml/l, is located below 300m depth in the Tumaco region, while off Cupica it is below 200m. Oxygen is thus not a limiting factor for the shelf fauna.
Panama
The surface temperature is pictured in Figure 6, while Figure 7a, b shows the two sections worked out in the gulfs of Panama and Cuiriqui. In relation to the conditions in Colombia, the hydro-graphic conditions in the Gulf of Panama can be seen as a prolongation of the uniform conditions more south. The surface temperature in the Gulf falls uniformly between the 28 and 29 degree, except off Punta Mala where a 1° decrease was observed. The hydrographical section in the Gulf wascarried out in the same position as the one of the previous survey. In contrast to the situation in February, no sign of upwelling can be observed. The 1 ml/l oxycline, which in February could be observed at 60 m bottom depth in the inner parts of the Gulf, was during this survey observed at 125 m, almost off the shelf edge. A pocket of oxygen-deficient waters was still found around 90 m bottom depth. This could be water trapped on the shelf as a consequence of the previous uppwelling period. Since February, the surface temperature has increased 4°C in the inner parts of the Gulf and the previous observed shoreward decreasing gradient has disappeared. In the Gulf of Chiriqui the surface temperature is 1 to 2°C higher as compared to the Gulf of Panama, as a result of the reduced influence of the northward current along the coast of Colombia. The situation is quite similar to the one observed in February, except for about one degree increase in the surface temperature.
Costa Rica
The surface waters (Figure 8) falls between 29 and 31°C, except for the inner parts of Gulf of Nicoya, where a slight reduction was observed. The hydrographic section carried out in this Gulf, pictured in Figure 9, shows a situation quite similar to the one observed during the previous survey. One hydrographical station was carried out in the Gulfo Dulce to see if any change had taken place in the subsurface waters. The situation was the same as observed in February.
