HR: 1330h
AN: OS23A-12    [Abstracts]
TI: Freshwater Influence Over the South Brazilian Continental Shelf: Indications From Foraminiferal Species Dominance
AU: * Eichler, P P
EM: patriciaeichler@gmail.com
AF: Delaware Geological Survey, Delaware Geological Survey Building, Newark, DE 19716-7501 United States
AU: Sen Gupta, B K
EM: barun@geol.lsu.edu
AF: Louisiana State University, 359 Howe-Russel Geoscience Complex, Baton Rouge, LA 70803-4101 United States
AU: Eichler, B B
EM: bbeichle@usp.br
AF: Instituto Oceanogr fico da Universidade de Sao Paulo, Pra‡a do Oceanogr fico, 191, Sao Paulo, SP 05508-900 Brazil
AU: Campos, E J
EM: edmo@io.usp.br
AF: Instituto Oceanogr fico da Universidade de Sao Paulo, Pra‡a do Oceanogr fico, 191, Sao Paulo, SP 05508-900 Brazil
AB: The 250-km-long Patos Lagoon covers an area of 10,360 km2 along the coastal plain of Rio Grande do Sul in southern Brazil. To the north, the 40-km-long Laguna estuarine system along the Santa Catarina coastline is essentially a series of choked coastal lagoons, with elliptical cells connected to the ocean via a single long and narrow channel. We examined the distribution of benthic foraminifera in samples collected from two continental-shelf transects, labeled the Albardäo transect (32° 58'S) and Santa Marta Cape transect (28° 34'S), in order to track the influence of the Patos Lagoon and the Laguna estuarine system in the dilution of shelf waters. In the Albardäo transect, we notice the dominance of Bulimininella elegantissima and Bolivina striatula live individuals in the shallower stations (15-42 m). These low-oxygen tolerant species are also found in muddy sediments of the Patos lagoon and near the mouth of the Plata River; their presence in shelf sediments indicates continental runoff in the region. Very large individuals of the agglutinated species Arenoparella mexicana and Gaudryina exilis (present in brackish waters Patos Lagoon) are found in water depths 19-54 m, also suggesting a strong and deep freshwater influence. At the 90-m isobath, (1) the species diversity shows a rise, and (2) larger agglutinated species and Buccela peruviana, a temperate/cold-water hyaline species, are occasionally present. B. peruviana is characteristic of assemblages influenced by the Malvinas Current, and indicates the presence of Sub-Antarctic Shelf Water (SASW). In contrast, the dominant species at 53 m on the Santa Marta Cape transect are Bulimina marginata and Pseudononion atlanticum. These species, together with small individuals of Arenoparella mexicana and Gaudryina exilis, show that the Santa Marta Cape area is under a major influence of Subtropical Shelf Waters (STSW), and that fresh-water influence is minor. The assemblage from the deepest stations on this transect (75, 109m) is dominated by Uvigerina peregrina and Cassidulina subglobosa, which indicates the presence of the cold, nutrient-rich South Atlantic Central Water (SACW).
DE: 3030 Micropaleontology
DE: 4283 Water masses
DE: 4804 Benthic processes/benthos
DE: 4815 Ecosystems, structure and dynamics
SC: Ocean Sciences [OS]
MN: 2005 Joint Assembly