© 2006 International Council for the Exploration of the Sea
Acoustic study of the Río de la Plata estuarine front
a Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP) Paseo V. Ocampo No. 1, Mar del Plata (B7602HSA), Argentina
b Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata Funes 3250, Mar del Plata (B7602HSA), Argentina
c Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) Rivadavia 1906, Buenos Aires (1033), Argentina
*Correspondence to A. G. Cabreira: tel: +54 223 4862586; fax: +54 223 4861830. e-mail: cabreira{at}inidep.edu.ar.
During December 1999, a transect 260 km long was carried out along the major axis of the Río de la Plata estuary. Acoustic (120 kHz), oceanographic, and zooplankton sampling were performed to extract a continuous, quasi-synoptic acoustic view of the estuary's salt wedge. Three different zones were identified. The riverine and marine zones were characterized by vertically homogeneous water and low volume-backscattering strength (Sv). The mixohaline zone was characterized by a strong vertical salinity gradient and the highest Sv values. There were no relationships between the reflection value calculated from the salinity gradient and suspended matter (sediments) and measured Sv. The greatest abundance of acoustically detectable organisms was at the halocline depth, coincident with the echo recordings. The positions of the halocline and the two fronts were determined on the basis of aggregations of the different planktonic groups. The physical presence of the salt wedge, as shown by a "biological wedge", was well described by the acoustic technique employed.
Keywords: acoustics, estuary, fronts, plankton, Río de la Plata, salt wedge
Received 12 August 2005; accepted 10 April 2006.
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