Islands

The islands that lie east of Madagascar (i.e. excluding those in the Mozambique Channel and the Comoros) all lie in the path of the South Equatorial Current. This wind-driven current is shallow and is considered not to change much in strength or direction, either seasonally or inter-annually. However, this conclusion may be the consequence of insufficient observations in the region. The effect of the passing water masses on the narrow shelf regions of most of the islands is not well known, but can be assumed to be a function of their offshore bathymetry and the absence or presence of coral reefs. The flow of the South Equatorial Current over the Mascarene Ridge that lies between Mauritius and the Seychelles has been established only recently. This shallow obstruction to the westward flow causes the current to be concentrated into a number of narrow jets through the deeper parts of the ridge. A seasonal phytoplankton bloom commences along the eastern coast of Madagascar with the onset of winter and progresses as a productivity wave eastwards as the seasonal thermocline deepens and nutrients from below are made available in the euphotic zone.

There is another important perturbation to the envisaged steady and invariant nature of this component of the ASCLME. It has been shown that meridional meanders in the South Equatorial Current travel westward as Rossby waves. Embedded in them are eddies. These eddies intensify as they move westward and may have a decisive influence on the ocean circulation of the islands they pass. It has been demonstrated that they, and eddies that come from the Mozambique Channel, may eventually reach the Agulhas Current and trigger Natal Pulses with all the attendant effects of current changes.

• < Prev
• Next >