The Congo River plume: Impact of the forcing on the far-field and near-field dynamics

The first numerical simulations of the Congo River plume dynamics are presented in this study. The different forcing mechanisms responsible for the seasonal variations of the plume extend are separately analyzed and the Regional Ocean Modeling System (ROMS) is employed to carry out both a process orientated study-with simple baseline simulations and a sensitivity study-with realistic 1 year runs setup in 2005. The baseline model is forced only by the river flow, in the presence of realistic bathymetry. Tides, wind stress, surface heat flux, and ocean boundary conditions are the forcing added to the realistic model. The typical seasonal orientation of the Congo River plume is found to be northward during most of year except for the February-March (FM) season when the plume has a large westward extension (about 800 km) and its area nearly doubles. The northward extension of the plume is explained by a buoyancy-driven upstream coastal flow-due to the unique geomorphology of the Congo River estuary-and the combined influences of the ambient ocean currents and the wind. During the FM season, the surface ocean circulation is driving both (1) the westward extension of the plume and (2) the southward transport of the Nyanga River fresh waters which feed the Congo River plume. In the near-field region of the plume, the presence of the deep Congo canyon has two main effects: (1) its depth increases the intrusion of sea water into the river mouth and (2) its orientation initiates the formation of the upstream flow.