Western Indian Ocean Journal of Marine Science

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Morphology of the Zambezi River plume in the Sofala Bank, Mozambique

Fialho PJ Nehama, Chris JC Reason


In this paper, hydrographic data collected in the vicinity of the Zambezi River plume between 2004-2007 is discussed alongside historical data to infer the plume morphology. The sampling plan called for 73 CTD stations that were interspersed with sampling of shrimp recruitment. Satellite-derived wind speed and river discharge collected at an upriver gauge station were also analysed. The dispersion patterns indicated a tendency of the plume to progressively propagate both in (equatorward) and against  (poleward) the sense of a coastally trapped wave.  This tendency had not been explored sufficiently in previous studies and it puts the Zambezi River plume in a short list of plumes across the globe that propagates in the direction opposite to the sense of a Kelvin or a shelf wave. Through visual inspection of the salinity distribution, the Zambezi plume was found to be super-critical (indicative of a faster freshwater inflow compared to the long internal wave phase speed), as well as surface-advected (bottom-advected) at times when the freshwater discharge rate measured at Tete was less than (more than)  2000 m3s-1. A clear distinction was found between the plumes of the Zambezi and Licungo rivers, characterized by a seaward bending of the salinity contours as the Zambezi freshwater flows downstream past the mouth of the Licungo River.

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