11 The Convergence Ecosystem
in the Southwest Atlantic
C. 0DEBRECHT and J.P. CASTELLO
11.1 Introduction
The Atlantic subtropical anticyclone and the antarctic circumpolar current
drive the upper oceanographic circulation in the Southwest Atlantic. The
large-scale flow field comprises the south and northward flowing western
boundary currents, the Brazil and Malvinas (=Falkland) currents, respectively. The Brazil Current transports warm tropical water (TW) during
most of the year towards the southern Brazilian shelf (Garcia 1997), while
the coastal branch of the Malvinas Current carries cool subantarctic water
(SAW) northwards. The confluence of Brazil and Malvinas currents represents part of the subtropical convergence and the mixture of TW and SAW
between about 25°S and 45°S forms the South Atlantic central water
(SACW). The two currents outline the eastern boundary of a large marine
ecosystem in the SW Atlantic between 23°S (Cabo Frio) and 55°S (Patagonia; Bisbal 1995; Fig. 11.1 ), separating it from the South Atlantic ocean
basin. The western boundary of the confluence approaches the southern
Brazilian, Uruguayan, and northeastern Argentinean coast, though latitudinal displacement occurs due to variability of the circumpolar antarctic
current (White and Peterson 1996). As a consequence, high variability of
physico-chemical and biological attributes occurs at the shelf and slope
system between approximately 30°S and 40°S due to the influence of horizontal, vertical, and seasonal mixing processes among TW, SACW, SAW,
and large continental runoff. High biological production conveys to this
system importance as a nursery, feeding, and reproduction area for fishery
stocks of both subtropical and antarctic origin, which utilize the western
boundary currents for long distance transport (Castello et al. 1997).
To comprehend the ecological variability of this warm transitional system
(Boltovskoy et al. 1996), however, oceanographic processes within the
larger ecosystem limits (23°S to 55°S) need to be considered.
Ecological Studies, Vol. 144
U. Seeliger and B. Kjerfve (eds.)
Coastal Marine Ecosystems of Latin America
©Springer-Verlag Berlin Heidelberg 2001
in the Southwest Atlantic
C. 0DEBRECHT and J.P. CASTELLO
11.1 Introduction
The Atlantic subtropical anticyclone and the antarctic circumpolar current
drive the upper oceanographic circulation in the Southwest Atlantic. The
large-scale flow field comprises the south and northward flowing western
boundary currents, the Brazil and Malvinas (=Falkland) currents, respectively. The Brazil Current transports warm tropical water (TW) during
most of the year towards the southern Brazilian shelf (Garcia 1997), while
the coastal branch of the Malvinas Current carries cool subantarctic water
(SAW) northwards. The confluence of Brazil and Malvinas currents represents part of the subtropical convergence and the mixture of TW and SAW
between about 25°S and 45°S forms the South Atlantic central water
(SACW). The two currents outline the eastern boundary of a large marine
ecosystem in the SW Atlantic between 23°S (Cabo Frio) and 55°S (Patagonia; Bisbal 1995; Fig. 11.1 ), separating it from the South Atlantic ocean
basin. The western boundary of the confluence approaches the southern
Brazilian, Uruguayan, and northeastern Argentinean coast, though latitudinal displacement occurs due to variability of the circumpolar antarctic
current (White and Peterson 1996). As a consequence, high variability of
physico-chemical and biological attributes occurs at the shelf and slope
system between approximately 30°S and 40°S due to the influence of horizontal, vertical, and seasonal mixing processes among TW, SACW, SAW,
and large continental runoff. High biological production conveys to this
system importance as a nursery, feeding, and reproduction area for fishery
stocks of both subtropical and antarctic origin, which utilize the western
boundary currents for long distance transport (Castello et al. 1997).
To comprehend the ecological variability of this warm transitional system
(Boltovskoy et al. 1996), however, oceanographic processes within the
larger ecosystem limits (23°S to 55°S) need to be considered.
Ecological Studies, Vol. 144
U. Seeliger and B. Kjerfve (eds.)
Coastal Marine Ecosystems of Latin America
©Springer-Verlag Berlin Heidelberg 2001