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cycle, four main periods can be distinguished as shown in Fig.
6
. From November to April
(low flow and ascending periods), the plume is carried northwestward with the NBC, while
the summer and fall display a plume mostly carried eastward as the seasonal NECC
retroflection strengthens. In comparison, the spatial pattern in the distributions of the
CDOM is in general very similar to SSS during the river discharge seasonal cycle.
However, the CDOM patterns can deviate from the SSS patterns at large distances from the
mouth of the river for some period of the seasonal cycle. This is particularly evident in the
region around the northern Antilles and the Caribbean during the high-flow season of 2010
(Fig.
6
, third panel from top) whereby high CDOM values are detected north of the low-
salinity plume extent (contours at SSS = 35.5 on the right panels), suggesting the presence
of dissolved organic matter concentrations that are non-correlated with the Amazon River
plume dilution. Altogether, this demonstrates the strength in combining satellite SSS
observations with complementary satellite observations in order to better characterize the
variability of the pathway of freshwater runoff along with the corresponding mixing
processes at seasonal to interannual time scales.
Quasi-linear relationships between SMOS SSS and the MERIS/MODIS CDOM
absorption coefficient (acdm) estimated for year 2010 are illustrated in Fig.
7
. Acdm
values were averaged over SSS bins with 0.5 bin width. As evidenced, while CDOM
mixing processes seem to be conservative on average, clear departure from linearity is
observed below 30 pss during the descending and low-flow seasons. This fact potentially
indicates changes in the endmember values at the mouths of the rivers and tributaries and/
or illustrate the occurrence of non-conservative mixing processes as listed above. Thanks
to the new satellite observations, departure from conservative mixing and the interannual
sources of variability will be certainly more detailed in the next future.
Fig. 5 Amazon (blue) and Orinoco (red) river discharge cycles measured, respectively, at Obidos and
Bolivar gauges, during the period 2010-2012. The black curve is showing the Amazon River discharge
climatology from 1968 to 2012
