South Atlantic Gyre

South Atlantic Gyre
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Name	South Atlantic Gyre
Location	South Atlantic Ocean
Type	Subtropical gyre
Major currents	Brazil Current; Benguela Current; South Atlantic Current; South Equatorial Current
Area km2	approx. 20,000,000
Dominant wind	South Atlantic Anticyclone
Notable features	Atlantic Meridional Overturning Circulation interaction; South Atlantic Convergence Zone

South Atlantic Gyre The South Atlantic Gyre is a large subtropical circulation system in the South Atlantic Ocean bounded by the coasts of South America, Africa, and the Southern Ocean. It integrates major boundary currents such as the Brazil Current, the Benguela Current, and the South Equatorial Current with the eastward South Atlantic Current to form a clockwise basin-scale circulation. The gyre influences regional climate variability linked to the South Atlantic Convergence Zone, the Intertropical Convergence Zone, and teleconnections with the El Niño–Southern Oscillation and Southern Annular Mode.

Overview

The gyre occupies much of the South Atlantic basin between the Equator, the ~30°S, and the eastern and western continental shelves adjacent to Brazil and Namibia/South Africa. It is centered beneath the semi-permanent high-pressure cell known as the South Atlantic High (also called the South Atlantic Anticyclone), which modulates the strength of the Bermuda-Azores High counterpart in the North Atlantic and interacts with the Atlantic Meridional Overturning Circulation. The gyre has been a focus of studies by institutions such as the Woods Hole Oceanographic Institution, the Scripps Institution of Oceanography, and the South African National Antarctic Programme.

Physical Characteristics

Sea surface temperature and salinity gradients within the basin reflect inputs from the Amazon River, the Congo River, and the inflow of subtropical waters from the Indian Ocean via the Agulhas Current retroflection and rings. The gyre’s central region is characterized by relatively low nutrient concentrations and elevated levels of marine debris accumulation because of convergent surface currents, creating an offshore zone analogous to the North Pacific Garbage Patch. Bathymetry across the basin includes the Mid-Atlantic Ridge and abyssal plains that influence deep-water pathways connected to the Antarctic Circumpolar Current and the Brazil Basin.

Circulation and Dynamics

Wind forcing from the South Atlantic Anticyclone drives the trade wind–forced South Equatorial Current westward and the westerlies that drive the eastward South Atlantic Current. Western boundary intensification produces the warm, poleward-flowing Brazil Current, while eastern boundary upwelling supports the equatorward Benguela Current. Eddy dynamics produce mesoscale features including Agulhas rings-like analogues, rings shed from the Brazil–Malvinas confluence near the Rio de la Plata, and intense fronts at the Brazil–Malvinas Confluence and the Cape Frio region. Interaction with the Atlantic Meridional Overturning Circulation and deep western boundary currents links surface gyre variability to broader Atlantic multidecadal variability documented by the Intergovernmental Panel on Climate Change assessments.

Climate and Oceanographic Impacts

The gyre modulates regional climate by controlling sea surface temperatures that affect precipitation over southern Brazil, Uruguay, Angola, and Namibia. Variability in gyre strength correlates with shifts in the South Atlantic Convergence Zone position and intensity, with downstream impacts on the Amazon Rainforest hydroclimate and agricultural regions such as the Cerrado. Sea level anomalies along the eastern South American shelf are tied to changes in the Brazil Current and have implications for port cities like Rio de Janeiro and Montevideo. Long-term changes in gyre circulation are monitored as potential contributors to altered heat transport within the Atlantic Multidecadal Oscillation and its influence on Atlantic hurricane activity.

Marine Ecosystems and Biodiversity

Ecosystems within the gyre range from oligotrophic gyre centers to productive eastern boundary upwelling zones off Namibia and Benguela that support large fisheries targeting anchovy and sardine species, exploited by fleets from nations including Portugal, Spain, and South Africa. Biodiversity hotspots include upwelling-associated seabird colonies such as those near Namibia and pinniped populations around Falklands and Tristan da Cunha. Pelagic food webs involve pelagic predators such as tuna and swordfish, migratory megafauna tracked by tags deployed by programs run by BirdLife International partners and the International Whaling Commission research affiliates. The gyre’s oligotrophic core supports microbial communities studied by teams at the European Molecular Biology Laboratory and the Monterey Bay Aquarium Research Institute using genomic tools.

Human Impacts and Pollution

Human activities affecting the gyre include industrial fishing by fleets from China, Japan, Russia, Spain, and Portugal; oil and gas exploration offshore Brazil and Angola; and transoceanic shipping connecting ports such as Cape Town, Buenos Aires, and São Paulo. The region accumulates persistent pollutants such as microplastics, persistent organic pollutants catalogued under the Stockholm Convention, and heavy metals linked to mining operations in South Africa and Brazil. Marine debris accumulations mirror concerns raised in studies by National Oceanic and Atmospheric Administration and United Nations Environment Programme reports; invasive species transfer via ballast water is regulated under the International Maritime Organization conventions.

Research and Monitoring Methods

Observational networks combine satellite remote sensing missions including TOPEX/Poseidon, Jason-3, and MODIS with in situ arrays: drifting buoys from the Global Drifter Program, Argo profiling floats coordinated by the Argo program, and moored arrays deployed by consortia such as the CLIVAR project. Oceanographic expeditions by institutions including the National Oceanography Centre (UK), Centro de Investigaciones del Mar y la Atmósfera, and the South African Environmental Observation Network employ CTD casts, ADCP surveys, and autonomous gliders. Modeling efforts use coupled climate models developed by centers like the National Center for Atmospheric Research and the Max Planck Institute for Meteorology to simulate gyre responses to greenhouse gas forcing evaluated by the Intergovernmental Panel on Climate Change.

Category:Oceanic gyres Category:South Atlantic Ocean