Suspended matters mean distribution and seasonal cycle in the Río de la Plata estuary from in situ and remote observations

DIEGO MOREIRA; CLAUDIA G. SIMIONATO

Florianópolis

Conferencia; 1st Latin America Physics of Estuaries and Coastal Oceans conference; 2019

Federal University of Santa Catarina, Brazil

Draining the second largest basin of South America, the Río de la Plata (RdP) is one of the largest and most turbid estuaries of the world. Daily 1 km resolution MODIS-Aqua data were processed for surface inorganic suspended matter, providing 10 years of observations. The aim of this work is to analyze those data to characterize mean values and variability on seasonal time scales, so as to provide clues about the involved physical mechanisms. The analysis is complemented with in situ observations collected during six cruises to the area and from fixed instruments. The comparison between direct and remote sensed observations is satisfactory, showing a good agreement in the magnitude and spatial distribution of the mean suspended sediments concentration and its standard deviation. Results suggest that the surface suspended matters? concentration in the RdP is strongly associated with the hydrodynamics and the scales of variability of the tributaries and the winds. Then waves during storms would enhance vertical mixing, consequently increasing surface concentration. The concentration of suspended sediments rapidly falls seawards the Barra del Indio shoal, in the area of the salt wedge. Probably this is, at least in part, a consequence of flocculation. In the outer estuary, suspended matters concentration seems to be also strongly associated to the wind-forced motion of the fresh water plume. Suspended matter 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 a raise in the frequency of the storms in winter, increasing the frequency of strong wind events and, therefore, a growth of the frequency of higher waves, which resuspend the fine sediments and mix the column in this very shallow part of the estuary.