Suspended matters mean distribution variability in the Río de la Plata estuary and the adjacent shelf from Modis and in situ observations

SIMIONATO, C.G.; MOREIRA, D.; GOHIN, F.; CAYOCCA, F.; LUZ CLARA TEJEDOR, M.

Conferencia; 54th ECSA: Coastal systems under change: tuning assessment and management tools; 2014

10 years of daily intermediate (1 km) resolution MODIS-Aqua observations and in situ observations collected during six cruises and from fixed instruments are analyzed to characterize the mean surface suspended matters (SM) distribution and variability in the Río de la Plata estuary, so as to provide clues about the involved physical mechanisms. SM concentration maximizes along the southern coast of the upper and intermediate estuary and at the tips of Samborombón Bay. This seems to be linked with the higher solid discharge of the Paraná River flowing along the southern coast to the estuary, which receives most of the sediments load to the Río de la Plata, and with the stronger tidal currents along that coast and at the tips of Samborombón Bay, which would act re-suspending sediments near the bottom. Then wind waves during storms would enhance vertical mixing, consequently increasing the surface concentration. The concentration of SM rapidly falls in the area of the salt wedge, at least in part as a consequence of flocculation. In the outer estuary, SM concentration seems to be also strongly associated to the wind-forced motion of the fresh water plume. SM concentration exhibits a maximum in winter and a minimum in summer, that cannot be fully explained in terms of the cycle of the solid discharge of the tributaries, but seems to be related to an raise in the frequency of the storms in winter, increasing the frequency of strong wind events in the region and, therefore, a growth of the frequency of higher wind waves, which re-suspend the fine sediments and mix the column in this very shallow part of the estuary.