Sierra Leone - State of the Marine Environment 2015

Figure 6.3: Ecological process assessment for “most” places

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

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

Figure 6.4: Surface salinity (Lamin 2011)

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