Gulf of Guinea
Part of the north Atlantic’s Canaries Current continues along the African coast and into the Gulf of Guinea as the eastward-flowing Guinea Current. The main freshwater input to the gulf is provided by the Niger River, which has an extensive depositional fan, up to 2.5 miles (4 km) thick. An even greater source of fresh water for the south Atlantic is from the Congo River to the south. Large oil and gas reserves have accumulated in the sediments of the Niger Delta and Fan, and Nigeria is Africa’s biggest oil producer. Smaller deposits lie in the Congo Fan and in the continental shelf off Gabon, and deeper water in the Gulf of Guinea is now being explored for oil. When the Atlantic Ocean basin started to open 180 million years ago, three rifts opened up in the crust, forming a tectonic triple-junction. Two of the rifts continued opening to the south and the west, forming today’s south Atlantic Ocean. Activity in the third rift, to the northeast, ceased rather quickly. The site of this stalled spreading center is marked by a chain of extinct volcanoes, including the islands of Annabon, São Tomé, Principe, and Bioco in the Gulf of Guinea, and Mount Cameroon inland. São Tomé rises 6,640 ft (2,020 m) above sea level.