Walvis Ridge

Apart from the Mid-Atlantic Ridge, the Walvis Ridge and the Rio Grande Rise are the most distinctive feature of the South Atlantic sea floor. They originated from hotspot volcanism and together they form a mirrored symmetry across the Mid-Atlantic Ridge, with the Tristan Hotspot at its centre. Two of the distinct sections in the Walvis Ridge have similar mirrored regions in the Rio Grande Rise; for example, the eastern section of the Walvis Ridge evolved in conjunction with the Torres Arch (the western end of the Rio Grande Rise, off the Brazilian coast) and, as the South Atlantic gradually opened, these structures became separated. The complex of seamounts in the western end of the Walvis Ridge, however, does not have a similar structure on the American side, but there is a Zapiola Seamount Complex south of the eastern end of the Rio Grande Rise. The formation of this mirrored structure is the result of the opening of the South Atlantic some 120 Mya and the Paraná and Etendeka continental flood basalts, the lateral-most parts of the structure, formed at the beginning of this process in areas that are now located in Brazil and Namibia. The Tristan-Gough hotspot track first formed over the mantle plume that formed the Etendeka-Paraná continental flood basalts some . The eastern section of the ridge is thought to have been created in the Middle Cretaceous period, between . While the mantle plume remained large and stable, the eastern Walvis Ridge formed along with the Rio Grande Rise over the Mid-Atlantic Ridge. The Ewing Seamount is part of the ridge. Palaeoclimatic role The Eocene Layer of Mysterious Origin (Elmo) is a period of global warming that occurred , about two million years after the Paleocene–Eocene Thermal Maximum. This period manifests as a carbonate-poor red clay layer unique to the Walvis Ridge and is similar to the PETM, but of smaller magnitude. ==Oceanography==

The Walvis Ridge is a natural obstacle for the Agulhas rings, mesoscale warm core rings that are shed from the Agulhas Current south of the Agulhas Bank. In average, five such rings are shed each year, a number that varies considerably between years. The rings tend cross the Walvis Ridge at its deepest part, but they still lose transitional speed and many rings decay rapidly. Their transitional speed drops from 5.2±3.6 km/day to 4.6±3.1 km/day, but it is not clear how much the Walvis Ridge is responsible for this drop, since the rings' speed drops to 4.3±2.2 km/day between the Walvis Ridge and the Mid-Atlantic Ridge. The rings can cross the South Atlantic in 2.5–3 years but only two thirds make it farther than the Walvis Ridge. The Agulhas rings transport an estimated 1-5 Sv (millions m3/s) of water from the Indian Ocean to the South Atlantic. Originating around Antarctica, Antarctic Bottom Water (AABW) enters the Cape Basin between the Agulhas Bank and the Agulhas Ridge after which it flows west north of the Agulhas Ridge. AABW then retroflects at the south-western end of the Walvis Ridge, flows north-east along the ridge before being retroflected south by North Atlantic Deep Water, with which it exits the Cape Basin and flows into the Indian Ocean. ==References==