South Atlantic Ocean

• Category: Marine and Oceanic Biomes.
• Geographic Location: Atlantic Ocean south of the equator.
• Summary: The waters of the South Atlantic Ocean encompass a range of environments, from the harsh conditions of the near-Antarctic region to lush coral reefs in the tropical waters of Brazil.

The South Atlantic Ocean, the portion of the Atlantic that lies south of the equator, has historically been relatively untouched regarding economic exploitation. However, humanity's search for natural resources increasingly focuses on its waters.

The South Atlantic has an elongated S-shape and is most often divided into the South and North Atlantic at the Equator. The South Atlantic separates the continents of Europe and Asia from those of South and North America. It is second to the Pacific Ocean in terms of size. It is connected to the Pacific Ocean through the North Arctic Ocean and the South Drake Passage. While the North Atlantic is slightly larger, the South Atlantic is deeper and has a greater volume.

The South Atlantic Ocean, like other large ocean basins, has a gyre—the South Atlantic Gyre—at its heart. It circulates counterclockwise, bringing warm water poleward and cold water toward the Equator. Its western arm, the Brazil Current, is a weaker, southern counterpart to the North Atlantic's Gulf Stream, flowing south toward Antarctica. Off the tip of South America, it collides with the Malvinas (Falklands) Current, a north-flowing offshoot of the eastward-flowing Antarctic Circumpolar Current. Part of the Brazil Current breaks away in the vicinity of this confluence to form the eastward-flowing South Atlantic Current, which, upon reaching Africa, splits with a northward-flowing branch, forming the Benguela Current.

The Benguela Current follows the west coastline of Africa. Ekman transporta wind-driven forcetriggers upwelling of cold, nutrient-rich waters inshore of this current, creating conditions for traditionally rich fisheries in the upwelling zone. These are found off the southwestern coast of Africa and the Cape of Good Hope. As the Benguela Current flows northward, its waters warm. It turns westward near the Equator, becoming part of the South Atlantic Equatorial Current—the northern part of the South Atlantic Gyre. In the vicinity of Brazil's Cabo de Sao Roque, the South Atlantic Equatorial Current splits, one portion flowing north as the North Brazil Current, the other flowing south, becoming the Brazil Current and completing the circulation. The North Brazil Current is much stronger. Most of it flows northwestward into the Northern Hemisphere, but part of it splits off and flows eastward as the North Equatorial Counter Current.

Marine and Coastal Life

The upwelling zone of the Benguela has created conditions for rich fisheries of species such as rock lobster, pilchard, anchovy, Cape horse mackerel, and hake. Overharvesting, however, has depleted the stocks of rock lobster and pilchard, among other species. Other notable species include the jackass penguin and several sea mammals, such as the Cape fur seal, southern right whale, and Heaviside's dolphin. Kelp forests, similar to those that occur off the coast of California, are locally important.

The cold, stormy waters of the southwest Atlantic have been havens for a wide variety of marine life, offering breeding areas for aquatic birds and mammals—including Magellanic penguin, imperial cormorant, pale-faced sheathbill, southern right whale, humpback whale, Commerson's dolphin, southern elephant seal, southern sea lion, and South American fur seal. The whaling and sealing industries began taking a heavy toll on many marine mammal species in the nineteenth century. Currently, the region supports economically important fisheries for hake, common squid, shortfin squid, and other species.

In subtropical and tropical waters farther north, collisions of warm currents with upwelling zones support a diverse environment, including mangroves and coral reefs. The beaches are critical nesting areas for leatherback, green, hawksbill, olive ridley, and loggerhead turtle communities. The waters are important tropical breeding areas for humpback whales and the smalleye hammerhead.

The South Atlantic features several isolated islands or island groups that encompass significant environmental and biological diversity. South Georgia and the South Sandwich Islands feature mountain ranges covered by snow and ice; their coastlines are breeding grounds and havens for marine birds and mammals.

Near the equator, Ascension Island—roughly midway between Africa and South America—appears to be the definitive desert island on land and at sea. The large expanses of rust-brown volcanic cinder cones and grayish-white lava flows were once breeding grounds for several seabirds, including the wideawake tern and Ascension frigatebird. The island's beaches are important nesting sites for green and hawksbill turtles. The low-nutrient marine environment has no coral reefs and lacks the diversity of reef ecosystems at similar latitudes. Ascension's nearshore waters are noted for the abundance of black durgon and ocean triggerfish and also host several endemic speciesadapted and native uniquely to a biomesuch as resplendent angelfish and Lubbock's yellowtail damselfish.

Human Impacts

Many of the South Atlantic ecosystems had long been relatively sheltered from human activity. However, in the 20th century, a burgeoning human population began putting greater and greater demands on the environment. Petroleum exploration and development, for example, is bringing much-needed cash to developing nations of Africa and South America, but at the cost of environmental disruption because of construction and accidents, including oil spills. Additionally, introduced species ravage once-isolated regions, and coastal construction—such as for resorts in tropical areas—leads to increasing loss of natural coastal regions and seascapes. Newly discovered resources, such as deep-sea fisheries, are depleted before sufficient scientific understanding of the resource to guide the development of sound management policies. In addition to commercial fishing, whaling activity in the region has been a concern for many years. Since 1998, the International Whaling Commission has discussed a proposal to establish a sanctuary for whales in the South Atlantic on many occasions. However, in 2018, the proposal was blocked by pro-whaling nations. The proposal was submitted several times after this. However, by 2020, it had not received the two-thirds majority needed for approval.

Ocean pollution has also been a major issue. Like the North Atlantic and the Pacific, the South Atlantic has a "garbage patch" made up of plastic litter that has entered the ocean and been carried to the South Atlantic Gyre. The patch, smaller than its Pacific and North Atlantic counterparts, was first detected in 2014t had a maximum density of 100 pieces of litter per square kilometer.

Much work remains to be done to identify and understand the ecosystems of the South Atlantic. A further overriding concern is the oncoming suite of changes being wrought by global climate change. A heavier atmospheric carbon dioxide load migrating into seawater causes its acidification—a process with often striking negative effects on corals, crustaceans, mollusks, and other organisms whose ability to create their calcium structures is blocked by the unbalanced seawater chemistry. Ocean warmingand further south, melting sea icehas been shown to rather dramatically reduce the supply of Antarctic krill in the South Atlantic; the depletion of this bottom-of-the-pyramid food source directly affects the population stability of such higher animals as penguins and baleen whales. Several studies suggest that increased temperatures in the major surface currents along the southern African coast will likely cause increased rainfall in coastal areas, which would alter the mix and augment the amount of land-based pollutants and nutrients flowing into the South Atlantic.

Bibliography

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