Sea Surface Salinity Observations from Space with the SMOS Satellite: A New Means to Monitor the Marine Branch of the Water Cycle - The Earth's Hydrological Cycle - page 206

Fig. 8 Map of SMOS SSS in the Gulf of Guinea and Southeast Atlantic Ocean indicating the two largest
pools of low-salinity waters in the eastern tropical Atlantic: the Bight of Biafra (Guinean waters) and the
Congo River plume. The map was generated by averaging SMOS data over 2010-2012 considering only
data acquired during months of April
Koleshnikov 1973 ;Bornhold 1973 ; Wauthy 1977 ;Van Bennekom and Jager 1978 ; Eisma and
Van Bennekom 1978 ; Van Bennekom and Berger 1984 ; Piton and Wacongne 1985 ; Braga
et al. 2004 ; Reverdin et al. 2007 ; Vangriesheim et al. 2009 ; Lef`vre 2009 ). However, the
ensemble of in situ SSS data collected during the period 1977-2002 in the ETA is sparse, and
only enabled retrievals of low-resolution (1 9 1) monthly climatology of the SSS field
(Reverdin et al. 2007 ), as displayed in Fig. 9 . Note that since 2003, the in situ SSS sampling
has however improved with the increasing deployments and operations of Argo floats.
The monthly averaged SMOS SSS maps shown in Fig. 10 were generated by combining
SSS data over the SMOS 3-year life period. As evidenced in detail by these maps, con-
sistent with historical in situ observations, the Congo River plume is spreading north-
westward along the coast and mixes with southwestward flowing freshwater from the bight
of Biafra during February and March (Koleshnikov 1973 ; Wauthy 1977 ). In May (Van
Bennekom and Jager 1978 ), June-July (Bornhold 1973 ; Wauthy 1977 ), and August
(Koleshnikov 1973 ), the two fresh pools are disconnected with the Congo plume directed
in westerly direction, extending up to 800-1,000 km offshore, as far as 8E. In November,
a ''jet stream'' of low-salinity water is ejected from the estuary with a large velocity and
protrudes in WNW direction (Wauthy 1977 ). The plume extent can also show southward
and southwestward legs depending on the prevailing windstress in the Angola Basin (Van
Bennekom and Berger 1984 ; Dessier and Donguy 1994 ).
The dispersal patterns of the Congo River plume during all seasons can mostly be
included inside the rectangle domain shown in Fig. 8 . The 10-day running mean time
series of the SMOS SSS averaged over that spatial domain is shown in Fig. 11 together
with the time series of the river discharge measured at Brazaville gauge station during the
period 2010-2012. Maxima in the averaged SSS within that region occur regularly in
August at the time of the Congo River minimum discharge. Minima in SSS (detected