| Description |
This area contains one of the most extensive continental shelves in the world, which is influenced by narrow, intense western boundary currents. The southward-flowing Brazil Current dominates the northern part of the region while the northward-flowing Falkland Current dominates the southern part, both of which are confined to the shelf break and seaward. (Bakun, 1993) Most of this region is influenced by onshore wind transport, except off Cabo Frio at the extreme north of the region, where a seasonal, locally wind-driven upwelling regime exists Processes of enrichment, stability, and retention combine in various configurations to produce favorable reproductive habitat for small, pelagic-spawning clupeoids. (Bakun and Parrish, 1991)
South of the Southeast Brazilian bight, the Ekman transport tends to be directed onshore (Bakun and Parrish, 1991), leading to coastal convergence and downwelling. Major upwelling at the shelf break (Servicio de Hidrografia Naval, 1969; Podesta, 1990) in the southern portion of the LME results from the juxtaposition of the major western boundary current and the shelf, carrying nutrients shoreward across the shelf. In this area, major freshwater outflows and the interleaving of water masses associated with the confluence of the major western boundary flows promotes internal water-column stability. Associated surface fronts represent convergence zones that concentrate food particles. (Elgue, 1989)
Strong tidal mixing occurs over the continental shelf in the vicinity of Peninsula Valdes, homogenizing the entire water column in shallower areas. The mixed surface water is denser than adjacent surface waters, and the bottom water is less dense. The density difference results onshore flow at the surface and at depth as the less dense surface waters and denser bottom waters of the stratified zone override and wedge under the mixed layer, respectively, eventually becoming incorporated in the mixed zone. The mixed waters move offshore. (Bakun,1993)
Like LMEs 3 (California Current) and 29 (Benguela Current), this system exhibits a combination of three general factors associated with favorable reproductive habitat for anchovies and sardines, including: enrichment of the food web by physical processes (e.g., upwelling, mixing); opportunity for concentrated patch structure of food particles (e.g., lack of turbulent mixing and/or convergence in frontal structures); and the availability of mechanisms that promote retention of larvae within or transport larvae to appropriate habitat. The three factors combine favorably only in special configurations, as otherwise turbulence and mixing, may disperse larvae away from the food source. (Bakun,1993) (http://www.na.nmfs.gov/lme/text/lme14.htm). |
