The South Atlantic Ocean
The Atlantic is the second largest of the ocean basins, as well as the most researched. It is bordered by five of the seven continents, with the Americas to the West, Antarctica to the South and Europe and Africa to the East.
With an area of 106,460,000 square kilometres, it is just over half the size of the Pacific Ocean. The average depth of the Atlantic is 3.3 km. The deepest point is located at the Milwaukee Deep, within the Puerto Rico, where it is submerged to 8.4 km. For reference – Mount Everest’s height is just short of 9km. The Atlantic Ocean is separated into North and South halves by the Equatorial Counter Current at latitude 8° N.
The South Atlantic formed around 130 million years ago when Pangea began to split apart and water from Panthalassa (super-ocean) started to fill gaps between the South African and American Plate. Currently plate position is indicated by the presence of many slowly spreading ridges e.g. the mid-Atlantic ridge. The sites of these active plate boundaries occur where reduced volcanism resulted in trough formation. The South Atlantic has been considered a hotspot for evolution due to the location of mantle plumes (upwellings) along ridge axes originating from thermal boundary layers. Seamount locations are indicative of past African plate movement and activity. The South Atlantic is host to many salt basins e.g. Brazil contains a salt basin series divided by basement and volcanic highs. Halite and anhydrite (salts) deposition began in the Sergipe-Alagoas Basin 124.8 million years followed by deposition in the Kwanza Basin, Angola between 124.5 and 121 million years.
The Portuguese explorer Pedro Alvares Cabral reached Brazil in 1500 leading to the colonization of South America. The anti-clockwise current and wind system of the South Atlantic favours sailing from Western Africa to the Americas leading to an active economy in slavery between the two continents and the colonizing European states Spain and Portugal. The colonizers forced most of the native populations of South America into slavery to mine silver and gold in the new territories. Most European merchants traded with Brazil leading to 5.5 million African slaves surviving the passage to Brazilian ports. The entire Trans-Atlantic slave trade lead to 5.6 million people being transported from West Central Africa alone, affecting the regions severely. However, most academic works on Atlantic history are still focused on the north Atlantic to the detriment of Native American and slave trade history.
As Portugal and Spain monopolised the trade other European countries such as England, France and the Netherlands made alliances with pirates. The ships under the command of Sir Francis Drake, Sir Henry Mainwaring and Alexandre Exquemelin among others could attack the merchants easily as the transport was predictable and slow due to the predominant currents and winds in the area.
The South Atlantic is home to a rich diversity of organisms. Of the 7000 zooplanktonic species found worldwide, roughly 60% are present in the South Atlantic. Around 90% of this geographic variation in zooplankton diversity can be explained by sea-surface temperatures and physical structure of the near surface. Interestingly, the diversity of foraminiferal plankton does not strictly follow the model of a continuous decrease in diversity from equator to pole, with a peak in the mid-latitude of the South Atlantic.
Although the superficial currents of the South Atlantic are known to serve as agencies of the transportation of planktonic organisms, the flow of the deeper currents drives differences in diversity between the near surface and deep-sea communities. Studies into the deep-sea Ostracod communities in the South Atlantic have revealed that faunal changes occurred alongside glacial/inter-glacial scale deep-water circulation fluctuations.
Some of the most charismatic and familiar animal species occur in the South Atlantic, such as the Atlantic yellow-nosed albatross (Thalassarche chlororhynchos), which nests on islands such as Tristan da Cunha and has a range expanding the South Atlantic to South America and Africa. The South Atlantic is also home to some of the most important fisheries, such as the Ascension longline fishery, which largely targets Bigeye tuna (Thunnus obesus). However, there is concern about the sustainability of the fishery, with sharks and turtles commonly caught as by-catch.
Deep sea corals are crucial ecosystem engineers and are important for the structural make-up of the reef. Especially for the Campos Basin region off the Brazilian coast, the corals have been found to support a wide range of carnivorous sponges.
It has long been considered that deep sea coral reefs could act as refuges for the shallower coral reef species who are more prone to influence from anthropogenic activities. However, recent studies have suggested that this is unlikely to be the case for the South Atlantic. There are currently only two species (Siderastrea stellata and Montastraea cavernosa) that are likely to be generalist and thus capable of surviving at greater depths than their current home range. In addition, the western area of the Atlantic shows a high level of endemism (species only found in one region and nowhere else) but low levels of species diversity including species of the Mussismilia genus.
For the South Atlantic Ocean, you can check out the following case studies: