Figure 2 shows the distribution of the surface temperature and Figure 3 the temperature, salinity and oxygen in the profiles off Trinidad’s north coast, from Mayaro Bay towards east and across the mouth and along the Colombus Channel. The combined analysis of the surface temperature chart and the profiles gives the following picture: There is a surface layer of very low salinity which covers the whole of the Colombus Channel area and the inner banks along the East Coast with traces also inshore off the North Coast. This water originates from the discharges of the Orinoco and only forms a 5 -10 m deep layer with a sharp interface of discontinuity with the underlying high salinity - and much denser water. This discontinuity layer appears as a scattering layer on echo sounders which could be traced over the whole area. As a result of the prevailing currents the surface layer deepens towards the Serpenths Mouth and over the north part of the channel. The oceanographic data from the previous surveys indicate a clear seasonal trend in this hydrographic phenomenon which on the whole must have a major influence on the ecosystem of the affected parts of the shelf. The isolines for temperature, salinity and oxygen of the Trinidad - East profile lifts toward the coast indicating transport of water shore-wards over the shelf although the surface water inshore does not seem to be affected by this process. Upwelling probably does take place north of Trinidad as indicated by the lower surface temperature inshore and the isolines of the profile.
The near bottom water of the Columbus Channel is deficient in oxygen and this is probably related to the existence of thresholds restricting the interchange of water to the east and to a high rate of decomposition of organic matter in this relatively productive area.
