HR: 09:15h
AN: OS21A-03    [Abstracts]
TI: Oceanography of the Subtropical Shelf Front Zone in the SW-Atlantic Continental Shelf
AU: * Muelbert, J H
EM: docjhm@furg.br
AF: Fundacao Universidade Federal do Rio Grande, FURG, Rio Grande, RS Brazil
AU: Acha, M
EM: macha@inidep.edu.ar
AF: Instituto Nacional de Investigaci˘n y Desarollo Pesquero, INIDEP, Argentina
AU: Acha, M
EM: macha@inidep.edu.ar
AF: Universidad Nacional de Mar del Plata, UNMdP, Argentina
AU: Berasategui, A
EM: alejandroberasategui@inidep.edu.ar
AF: Instituto Nacional de Investigaci˘n y Desarollo Pesquero, INIDEP, Argentina
AU: Bersano, J G
EM: docber@furg.br
AF: Fundacao Universidade Federal do Rio Grande, FURG, Rio Grande, RS Brazil
AU: Braga, E S
EM: edsbraga@usp.br
AF: Instituto Oceanografico da Universidade de Sao Paulo, IOUSP, Brazil
AU: Eichler, P
EM: patrciaeichler@gmail.com
AF: University of Delaware, Delaware Geological Survey, United States
AU: Garcia, V M
EM: docvmtg@furg.br
AF: Fundacao Universidade Federal do Rio Grande, FURG, Rio Grande, RS Brazil
AU: Gomez-Erache, M
EM: mge@fcien.edu.uy
AF: Universidad de la Replublica, FCIEN, Uruguay
AU: Guerrero, R
EM: raul.guerrero@inidep.edu.ar
AF: Instituto Nacional de Investigaci˘n y Desarollo Pesquero, INIDEP, Argentina
AU: Guerrero, R
EM: raul.guerrero@inidep.edu.ar
AF: Universidad Nacional de Mar del Plata, UNMdP, Argentina
AU: Mianzan, H
EM: hermes@inidep.edu.ar
AF: Instituto Nacional de Investigaci˘n y Desarollo Pesquero, INIDEP, Argentina
AU: Mianzan, H
EM: hermes@inidep.edu.ar
AF: Consejo Nacional de Investigaciones Cientificas y Tecnicas, CONICET, Argentina
AU: Reta, R
EM: reta@inidep.edu.ar
AF: Instituto Nacional de Investigaci˘n y Desarollo Pesquero, INIDEP, Argentina
AU: Reta, R
EM: reta@inidep.edu.ar
AF: Universidad Nacional de Mar del Plata, UNMdP, Argentina
AU: Ramirez, F
EM: framirez@inidep.edu.ar
AF: Instituto Nacional de Investigaci˘n y Desarollo Pesquero, INIDEP, Argentina
AB: Only physical aspects of the Subtropical Shelf Front (STSF) have been described for the Southwest Atlantic Continental Shelf. The main goal of this paper is to present results of an integrated physical, chemical and biological study at the STSF conducted during the winter of 2003 and summer of 2004. A cross section was established at the historical determined location of the STSF. Nine stations were sampled during the winter cruise and 7 stations during summer. Each section included a series of conductivity-temperature-depth (CTD) stations fitted with dissolved oxygen and turbidity sensors. Selected water samples were filtered and frozen at -20^oC for nutrient determination. Samples for chlorophyll were concentrated on filters and these were stored frozen for later processing. Plankton net tows were carried out above and below pycnocline. Surface benthic foraminifera were collected with a bottom snapper. Results revealed that winter was marked by an inner shelf salinity front and the STSF located in the mid-shelf. Inner salinity showed the strong influence of freshwater, with high silicate (71.98 μM), phosphate (2.70 μM), nitrate (1.01 μM), Total Dissolved Nitrogen (22.98 μM) and suspended matter (44.80 mg/L). With distance from the coast and reduction of terrestrial input, subsurface high values of nutrients were associated with SACW upwelling. As a result, chlorophyll a concentration decreased from coastal well-mixed waters, where values up to 3.0 mg.m³ are registered, to offshore waters. Zooplankton abundance and biomass, and ichthyoplankton abundance follows the same trend. Zoo and ichthyoplankton abundance revealed the presence of 3 groups associated to the inner, mid and offshore shelf region. Benthic foraminifera composition suggested that shallow stations are dominated by few large freshwater species, while offshore stations presented smaller forms and higher species diversity. During summer, the halocline extended over the shelf and joined the STSF in the upper layer. The concentration of inorganic nutrients is reduced in the shallow waters in relation to the winter period, but high values are observed between 40 and 60 m depth and offshore deep waters. Zooplankton biomass was not as high as during winter, and largest values are observed around the STSF. Zoo and ichthyoplankton presented 3 groups, separated by the presence of the STSF. Despite less influence of freshwater during this season, benthic foraminifera were still marked by the presence of freshwater species. The results from this study suggest that during winter, freshwater influence is strong and physical-chemical-biological interactions develop in the front along its plume. However, during summer, when the presence of freshwater is less intense, these interactions seem to take place at the STSF.
DE: 4215 Climate and interannual variability (3309)
DE: 4219 Continental shelf processes
DE: 4227 Diurnal, seasonal, and annual cycles
DE: 4546 Nearshore processes
DE: 4815 Ecosystems, structure and dynamics
SC: Ocean Sciences [OS]
MN: 2005 Joint Assembly