32 / 74
32
Mean temperature profiles up to 500m depth in the area
of the continental shelf show the development of a sharp
thermocline below the warm surface waters. The gradient
of temperature here sometimes exceeds 3°C per 10m.
Below the thermocline temperatures continue to fall
gradually with depth.
It is worth noting that the global rise in SST has not caused
any significant local impacts in Sierra Leone.
6.2. Salinity
The average salinity of the sea surface waters off the Sierra
Leonean coast is generally less than 35.5 psu (Fig. 6.4).
The salinity is influenced by fresh water run-off from
land and rainfall especially during the rainy season. Mean
salinity profiles in the shallow areas close to the coast are
characterized by low salinities at the surface, which result
from the inflow of fresh water. The limits of the salinity
homogeneous layer correspond to the upper limits of
the thermocline showing that the salinity and thermal
structures are similar in the surface layer. Below the surface
a sub-surface salinity maximum (S=35.7°) exists between
60–70m depth. Below the maximum, salinity gradually
decreases to a minimum around 500m depth.
6.3. Ocean Currents
Currents are dynamic features of coastal waters of Sierra
Leone and affect the coastal zone in a number of ways. The
surface currents are significantly influenced by the Southeast
andNortheast tradewinds. During the spring in theNorthern
Figure 6.3:
Ecological process assessment for “most” places
Figure 6.4:
Surface salinity (Lamin 2011)