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

Abstract

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.