South African Ocean Currents There are few places on this blue planet that can match the marine diversity found along the shores of Southern Africa. Two very different oceanic currents flank the coast of the southern tip of the African Continent. While South Africa’s east coast is washed by the warm Agulhas current, which flows south- ward from tropical latitudes off Mozambique and Madagascar, the west coast is bathed in the cold wa- ters of the Benguela Current system. The main near-surface ocean circulations near South Africa are shown in these two images above: the Agulhas (aka Mozambique) current running on the east coast is relatively warm; whereas the Benguela current is cooled by coastal upwelling along the west coast of S. Africa and Namibia. The Agulhas current The Agulhas current is the Western Boundary Current of the southwest Indian Ocean and follows the edge of the continental shelf as it flows swiftly down the east coast of South Africa. The current reaches its maximum velocity about 2.5 meters per second, where the shelf narrows between Port Shepstone and East London. At the Southernmost tip of the continent, the current leaves the shelf edge at the shallow Agul- has Bank and turns back on itself in a loop, known as the Agulhas retroflection. Most of the water returns to the Indian Ocean, but sometimes the loop pinched off a huge eddy/ whirlpool, about 300 km in diameter known as the Agulhas Ring. This Agulhas ring moves into the Atlantic Ocean, where it may interact with the Benguela Current System. It is thought that this may negatively impact the commercial fishing industry by transporting the eggs and larvae of pelagic fish species from their nursery areas on the West Coast to the less productive waters offshore, where they are lost from the system. The Warm Agulhas Current, on the east coast, creates a more benign environment as the warm ocean releases: More moisture into the air generating more precipitation and creating a much greener landscape on land. Many more rivers enter the sea compared to the west coast Many more people settle along these shores, as fresh water is more abundant. For the first time semitropical flora and faunais seen along this coast. The unique flora is a mix of forest interspersed by thornveld and fauna like the Blue Duiker and Fish Eagle’s are just some of the animals that can be found here. The first large mangrove forests are found along the Mgazana Estuary on the Wild Coast. More species of fish have been recorded in tide pools of the east coast (66) than on the south coast (44) and the west coast (40). At the heart of the warm Algulhas Current is the iSimangaliso Wetland Park - South Africa’s first World Heritage Site with 332, 000 hectares that contains 3 major lake system and 8 interlinked eco- systems. It is also home to Africa’s largest estuarine system and includes large coastal forest dunes - some of the highest in the world. Lake St.lucia situated in the iSimangaliso Wetland Park This is a key marine protected area and an important breeding site for marine turtles in Africa. It is also a corridor for migratory humpback whales, dolphins and sharks. This Park is an icon in conservation along the warm Algulhas realm with a distinctive semitropical flavor. The Benguela Current The Benguela Current, on the west coast of Southern Africa, is part of the eastern portion of the South Atlantic Ocean system and is a slow northerly movement of water. The current moves at average speeds of 15-20 cm per second along the west coast, Strong southerly winds blowing parallel to the coastline in spring and summer drive the upwelling of cold, nutrient-rich water from the depths to the surface, making the Benguela current a highly productive system. This cold Benguela current release: Very little moisture into the air and most of the west coast is a rather semi-arid land with little fresh water available Therefore, fewer human settlements are found along these shores. The effects of the cold Benguela Current can be felt all the way along the coast to Algoa Bay in Port Elizabeth This will also explain the large concentration of breeding Cape Gannets and African Penguins in that area. The rich nutrients in this water encourage the growth off: Dense phytoplankton blooms, which supports huge schools of pelagic fish, such as anchovy and sardine. This is also the starting point of the famous South African ‘sardine run’. These are in turn food for larger fish, seabirds, dolphins and seals. Giant kelp plants also dominate the shallow reefs along the Benguela and it is under the shelter of this golden forest that there are a myriad of life with many dense communities of mussels, sponges, sea urchins, sea cucumbers, abalone and the endemic West Coast Rock Lobster. The west coast of South Africa has some impressive records as the world largest biomass of marine flesh of grazers per unit of rock, because off all the dense communities of mussels, sea urchins, sea cucumbers etc. Where do the Two Oceans meet? There has always been controversy about the exact meeting point of the Atlantic and the Indian Ocean off the southern tip of Africa. There is no particular place where the two oceans can be seen to meet in a line, it is a common mis- conception that the two oceans meet at the southernmost “tip of Africa” at Cape Agulhas, however the generally accepted meeting point of the two oceans is actually 200km south east at Cape Point . Cape Point South African Ocean Currents comprehension test 1) Match the two South African ocean currents with their ocean systems? Cold Benguela ocean current Warm Agulhas ocean current Indian Ocean Atlantic Ocean 2) Which Ocean current moves the fastest? ___________ 3) The warm Agulhas ocean current releases more or less moisture in the air than the cold Benguela current? ____ 4) Fill in the blanks? Strong ________winds blowing parallel to the coastline in spring and summer drive the upwelling of cold, nutrient-rich water from the depths to the surface in the Benguela current. Giant kelp plants also dominate the shallow reefs along the ________ current and it is under the shelter of this golden forest that there are a myriad of life with many endemic species. The cold Benguela current is richer in ________ than the warm Agulhas current; this explains the larger biomass of marine life along the colder currents. 5) True or false: You will find greener coastlines along the colder Benguela current than the warmer Agulhas current. 6) When the Agulhas current reaches the most southern tip of Africa it loops and turns back on itself, this is known as the Agulhas_______? 7) Sometimes this loop pinches off and forms an ‘Eddy’/whirlpool of about 300 km in diameter; this is known as the Agulhas ______? 8)True or false: The west coast of South Africa has some impressive records as the world largest biomass of marine flesh of grazers per unit of rock. 9) Name the wetland park found on the east coast of Southern Africa along the Agulhas current, which contains numerous lakes and estuaries? _________________ 10) Explain why we find more estuaries and lakes along the Agulhas current coastline than the Benguela current? __________________ .