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together with the Niger, Volta and numerous other smaller rivers (Fig.
8
). In addition,
intense precipitations also decrease SSS in the Guinea current and northeastern Gulf of
Guinea (Hisard
1980
; Merle
1980
). The ETA is therefore characterized with a highly
complex hydrographic system, largely influenced by the Congo River, intense precipita-
tion, and strong seasonal coastal and equatorial upwelling in the boreal summer.
Maximum discharge from the Congo River occurs in December and minimum discharge in
March through April. The outflow is hardly detectable from SST or sea level data. In chloro-
phyll, however, the mouth of the Congo River shows a strong signal all year round with large
plumes extending offshore. While these ocean color signals highlight real oceanographic
features of the plume, frequent cloud cover found in this region during the rainy season strongly
inhibits the spatiotemporal evolution of the Congo plume structure to be monitored.
Hitherto the knowledge about the seasonal extension and spreading of the Congo River
plume is therefore mainly relying on dedicated in situ surveys (e.g., see Meulenbergh
1968
;
Fig. 7 a
CDOM
(490) to SMOS SSS dependence in the western tropical North Atlantic averaged over years
2010-2012 for all seasons of the Amazon River Discharge cycle (Top) and for each season separately
(bottom). In the upper panel, the mean a
CDOM
(490) per 0.5 bins is shown as a solid black line ±1 standard
deviation (vertical bars)
