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Chapter 9: The Atlantic Ocean
Brazil Current Coastal Province (BRAZ)
Extent of the Province
The northern boundary of the BRAZ province is placed near Recife (8
S), where the
coast of South America changes orientation, and close to the partition of the flow of
the transoceanic SEC between this province and Amazon Shelf of the GUIA province.
The BRAZ province extends down the east coast of South America to about 35
S,
off Argentina, where the northward flow of the Falkland Current is encountered. This
important confluence region is discussed in the next section, devoted to the FKLD
province. The outer boundary of the rather narrow BRAZ province seldom occurs beyond
the 2000-m contour.
Continental Shelf Topography and Tidal and Shelf-Edge Fronts
This coast is remarkably straight and the shelf usually rather narrow: in the north it
reduces to a width of only 10 km. The only topographic features of importance are near
25
S, where there are two prominent capes: Cabo Sao Thomé and Cabo Frio (both this
and the similarly named cape in the Benguela Province owe their name to the same
phenomenon—upwelling). At 16–17
S, the shelf has a complex topography of valleys
and submarine canyons, and the wide Abrolhos and Royal Charlotte Banks emerge from
great depths and bear hermatypic coral formations, almost the most southerly reefs in the
South Atlantic. In the bight to the south of Rio de Janeiro, the shelf widens to 200 km,
and the sediments lack the calcareous components characteristic of lower latitudes. There
are no canyons here, but numerous topographic depressions, holding soft sediments,
characterize this section of shelf. Along the Argentinian coast, deep water lies unusually
close inshore.
Defining Characteristics of Regional Oceanography
The Brazil Current (BC) is the weakest of the western boundary currents because only
about one quarter of the westward flow across the equatorial southern Atlantic of the
SEC enters the BC. As noted previously, the remainder flows northward into the incipient
NBC, rather than remaining in the southern hemisphere subtropical gyre (Peterson and
Stramma, 1991; Gordon and Greengrove, 1986). South of 30
S, the BC strengthens (at
about 5% per 100 km from 20
S to 35
S) by entrainment from a recirculation cell lying
between the continent and the Rio Grande Rise. This gyre originates at the confluence
of the BC and the northward flow of the Falkland Current (Castro and de Miranda,
1998).
Wind stress over the BC responds to the seasonal migration of the ITCZ that lies
between trade winds and westerlies; during austral summer prevailing winds are from
the E or NE over the entire region, whereas during austral winter, to south of Cabo
Frio, winds are coastwise and dominantly from the SW while, to the north of this
cape, the dominant direction is increasingly from the SE, or directly onshore. Repeated
westerly waves and cold fronts propagate equatorward along the coast at 5- to 10-day
intervals, reach Recife in austral summer, and dominate the synoptic weather pattern at all
seasons.
As the oligotrophic, nutrient-poor water of the Brazil Current proceeds southward, its
maximum flow lies over the shelf edge but transport extends across the shelf, especially
in austral summer. In austral winter, flow retreats to beyond the shelf break. Seasonal
variation in mass transport (maximal in austral summer and minimal in winter) is directly
related to the seasonal change in wind stress curl. The strongest (weakest) transport
occurs when the confluence region is furthest south (north), according to Matano et al.
Chapter 9: The Atlantic Ocean
Brazil Current Coastal Province (BRAZ)
Extent of the Province
The northern boundary of the BRAZ province is placed near Recife (8
S), where the
coast of South America changes orientation, and close to the partition of the flow of
the transoceanic SEC between this province and Amazon Shelf of the GUIA province.
The BRAZ province extends down the east coast of South America to about 35
S,
off Argentina, where the northward flow of the Falkland Current is encountered. This
important confluence region is discussed in the next section, devoted to the FKLD
province. The outer boundary of the rather narrow BRAZ province seldom occurs beyond
the 2000-m contour.
Continental Shelf Topography and Tidal and Shelf-Edge Fronts
This coast is remarkably straight and the shelf usually rather narrow: in the north it
reduces to a width of only 10 km. The only topographic features of importance are near
25
S, where there are two prominent capes: Cabo Sao Thomé and Cabo Frio (both this
and the similarly named cape in the Benguela Province owe their name to the same
phenomenon—upwelling). At 16–17
S, the shelf has a complex topography of valleys
and submarine canyons, and the wide Abrolhos and Royal Charlotte Banks emerge from
great depths and bear hermatypic coral formations, almost the most southerly reefs in the
South Atlantic. In the bight to the south of Rio de Janeiro, the shelf widens to 200 km,
and the sediments lack the calcareous components characteristic of lower latitudes. There
are no canyons here, but numerous topographic depressions, holding soft sediments,
characterize this section of shelf. Along the Argentinian coast, deep water lies unusually
close inshore.
Defining Characteristics of Regional Oceanography
The Brazil Current (BC) is the weakest of the western boundary currents because only
about one quarter of the westward flow across the equatorial southern Atlantic of the
SEC enters the BC. As noted previously, the remainder flows northward into the incipient
NBC, rather than remaining in the southern hemisphere subtropical gyre (Peterson and
Stramma, 1991; Gordon and Greengrove, 1986). South of 30
S, the BC strengthens (at
about 5% per 100 km from 20
S to 35
S) by entrainment from a recirculation cell lying
between the continent and the Rio Grande Rise. This gyre originates at the confluence
of the BC and the northward flow of the Falkland Current (Castro and de Miranda,
1998).
Wind stress over the BC responds to the seasonal migration of the ITCZ that lies
between trade winds and westerlies; during austral summer prevailing winds are from
the E or NE over the entire region, whereas during austral winter, to south of Cabo
Frio, winds are coastwise and dominantly from the SW while, to the north of this
cape, the dominant direction is increasingly from the SE, or directly onshore. Repeated
westerly waves and cold fronts propagate equatorward along the coast at 5- to 10-day
intervals, reach Recife in austral summer, and dominate the synoptic weather pattern at all
seasons.
As the oligotrophic, nutrient-poor water of the Brazil Current proceeds southward, its
maximum flow lies over the shelf edge but transport extends across the shelf, especially
in austral summer. In austral winter, flow retreats to beyond the shelf break. Seasonal
variation in mass transport (maximal in austral summer and minimal in winter) is directly
related to the seasonal change in wind stress curl. The strongest (weakest) transport
occurs when the confluence region is furthest south (north), according to Matano et al.