Acoustic study of the Río de la Plata estuarine front.

CABREIRA, A.; MADIROLAS A.; ALVAREZ COLOMBO G.; ACHA E.M.; MIANZAN H. W.

ICES JOURNAL OF MARINE SCIENCE

Año: 2006 vol. 63 p. 1718 - 1725

1054-3139

During December 1999, a transect 260 km in length was carried out along the major axis of the Río de la Plata estuary. Acoustic (120 kHz), oceanographic and zooplankton sampling were performed to present a continuous, quasi-synoptic acoustic view of the estuary salt wedge. Three different zones were identified. The riverine and marine zones were characterized by vertically homogeneous waters and low volume-backscattering strength (Sv). The mixohaline zone was characterized by a strong vertical salinity gradient and the highest  Sv values. No relationship between the salinity gradient and suspended matter (sediments) with the measured Sv was observed. The highest abundances of acoustically detectable organisms were found mainly concentrated at the halocline depth, coincident with the echo recordings. The halocline and the two fronts resulting from the aggregations of different planktonic groups were determined. The physical presence of the salt-wedge as shown by a “biological wedge” was quite well described by the acoustic techniques used.