146
E. V. Djagoua et al.
(Herbland and Le Loeuff 1993), reaching a peak outflow in October. This period
of high river discharge corresponds also to the end of the main upwelling period,
when the CHL contribution has already started to decrease. Once again, the timing
of these events would agree rather well with the mix of the (increasing) CDOM and
(decreasing) CHL percent contributions in the period of transition between GCS and
SWS.
7.4 Conclusions
The analysis of the R rs spectral components, in the annual, seasonal and monthly
composite images derived from a 2003–2007 time series of SeaWiFS data, has shown
the relative proportions of the main water constituents present in the Côte d’Ivoire
coastal waters at the Sassandra river mouth. The ternary plots of the percent reflectance attributed to CDOM, CHL and DET suggest that, in the area considered,
the water constituents follow trends linked to the successive “marine” seasons of
the area. The onset of upwelling events, which bring to coastal waters the nutrients
required for a sustained photosynthetic activity of phytoplankton, seem to be the
key to environmental dynamics of the whole region. However, the hinted coupling
of yellow substance variations to the weakening of upwelling and to the discharge
of local rivers (otherwise flowing through large deforested areas), is an element that
points to a strong anthropogenic impact on the coastal environment. The indications
emerging from the present study, albeit approximate and very preliminary, provide
an example of the important role to be played by RS in managing the area adjacent
to the Sassandra river mouth (where in situ data are sparse). In the future, such a
role could be extended to the entire coastline of the Côte d’Ivoire, in order to better
classify marine waters impacted by natural processes such as coastal upwelling or
by anthropogenic pollution due to river runoff.
Acknowledgments The SeaWiFS data used in this paper were obtained through the GIOVANNI
online data system, developed and maintained by the NASA Goddard Earth Sciences Data and
Information Services Center (GES DISC). The authors wish to express their gratitude to Global
Ocean Observing System (GOOS) Africa, Interim Guinea Current Commission (IGCC) Guinea
Current Large Marine Ecosystem (GCLME) project, and United Nations Educational, Scientific
and Cultural Organization (UNESCO) for the support granted to the present work. Special thanks
are due to the Joint Research Centre (JRC), European Commission (EC) for the opportunity to
publish in this volume devoted to the African Seas.
References
Bakun A (1978) Guinea current upwelling. Nature 271:147–150
Binet D (1997) Climate and pelagic fisheries in the Canary and Guinea currents 1964–1993: the
role of trade winds and the southern oscillation. Oceanologica Acta 20:177–190
E. V. Djagoua et al.
(Herbland and Le Loeuff 1993), reaching a peak outflow in October. This period
of high river discharge corresponds also to the end of the main upwelling period,
when the CHL contribution has already started to decrease. Once again, the timing
of these events would agree rather well with the mix of the (increasing) CDOM and
(decreasing) CHL percent contributions in the period of transition between GCS and
SWS.
7.4 Conclusions
The analysis of the R rs spectral components, in the annual, seasonal and monthly
composite images derived from a 2003–2007 time series of SeaWiFS data, has shown
the relative proportions of the main water constituents present in the Côte d’Ivoire
coastal waters at the Sassandra river mouth. The ternary plots of the percent reflectance attributed to CDOM, CHL and DET suggest that, in the area considered,
the water constituents follow trends linked to the successive “marine” seasons of
the area. The onset of upwelling events, which bring to coastal waters the nutrients
required for a sustained photosynthetic activity of phytoplankton, seem to be the
key to environmental dynamics of the whole region. However, the hinted coupling
of yellow substance variations to the weakening of upwelling and to the discharge
of local rivers (otherwise flowing through large deforested areas), is an element that
points to a strong anthropogenic impact on the coastal environment. The indications
emerging from the present study, albeit approximate and very preliminary, provide
an example of the important role to be played by RS in managing the area adjacent
to the Sassandra river mouth (where in situ data are sparse). In the future, such a
role could be extended to the entire coastline of the Côte d’Ivoire, in order to better
classify marine waters impacted by natural processes such as coastal upwelling or
by anthropogenic pollution due to river runoff.
Acknowledgments The SeaWiFS data used in this paper were obtained through the GIOVANNI
online data system, developed and maintained by the NASA Goddard Earth Sciences Data and
Information Services Center (GES DISC). The authors wish to express their gratitude to Global
Ocean Observing System (GOOS) Africa, Interim Guinea Current Commission (IGCC) Guinea
Current Large Marine Ecosystem (GCLME) project, and United Nations Educational, Scientific
and Cultural Organization (UNESCO) for the support granted to the present work. Special thanks
are due to the Joint Research Centre (JRC), European Commission (EC) for the opportunity to
publish in this volume devoted to the African Seas.
References
Bakun A (1978) Guinea current upwelling. Nature 271:147–150
Binet D (1997) Climate and pelagic fisheries in the Canary and Guinea currents 1964–1993: the
role of trade winds and the southern oscillation. Oceanologica Acta 20:177–190