HR: 09:00h
AN: OS21A-02    [Abstracts]
TI: The Subtropical Shelf Front off Eastern South America: Winter 2003 and Summer 2004
AU: * Piola, A R
EM: apiola@hidro.gov.ar
AF: Servicio de Hidrograf¡a Naval, Av. Montes de Oca 2124, Buenos Aires, C1270ABV Argentina
AU: Moller, O O
EM: dfsomj@furg.br
AF: Funda‡ao Universidade Federal do Rio Grande, R. Eng. ALfredo Huch 475, Rio Grande, RS 96201-900 Brazil
AU: Guerrero, R A
EM: raul.guerrero@inidep.edu.ar
AF: Instituto Nacional de Investigaci¢n y Desarrollo Pesquero, Pje. Victoria Ocampo 1, Mar del Plata, BUE B7602HSA Argentina
AU: Campos, E J
EM: edmo@io.usp.br
AF: Universidade de Sao Paulo, Pca. do Oceanografico, 191 Cidade Universitaria, Sao Paulo, SP 05508-900 Brazil
AB: In Austral winter 2003 and summer 2004 we conducted two large-scale hydrographic surveys on the continental shelf and slope off eastern South America. Among other goals, the field work was designed to determine the relation between the low salinity waters derived from the Rio de la Plata, and the subsurface front found between Subantarctic Shelf Waters (SASW), derived from the Patagonia continental shelf, from Subtropical Shelf Waters (STSW), primarily influenced by the Brazil Current. In August 2003 the Plata plume extended beyond 26§S creating a region of strong vertical stratification in the offshore edge of the plume, near the 40 m isobath. The cross-shore salinity structure at Albardao (33§S) reveals two distinct salinity fronts: the inner shelf front at the offshore edge of the Plata plume and the STSF located in the mid-shelf. The plume front is isothermal and associated with a sharp density front while the STSF presents nearly density-compensating salinity and temperature gradients. Though the density gradients across the STSF are moderate, isopycnals intersect the sea surface and the bottom, inhibiting isopycnal mixing between SASW and STSW. The strong northeasterlies in February 2004 retracted the Plata plume to 32§S and expanded it to the shelf break. Consequently, the summer halocline extends over the entire shelf width causing the plume front to merge with the STSF in the upper layer. Off Albardao there is strong isopycnal mixing between mid-shelf and Brazil Current waters. The data reveal how seasonal changes in the upper layer associated to wind variations induce significant modifications of the lower layer water masses and completely rearrange the frontal structure. These thermohaline alterations are likely to have a profound impact on the distribution of species.
DE: 4243 Marginal and semienclosed seas
DE: 4283 Water masses
DE: 4528 Fronts and jets
DE: 4536 Hydrography
SC: Ocean Sciences [OS]
MN: 2005 Joint Assembly