This great mountain range is the site of submarine earthquakes, volcanos, and hydrothermal vents . These vents occur when water seeps through cracks in the seafloor and is then heated by underlying volcanic molten rock. The water then rises back to the ocean floor as mineral-rich hot water springs. The Mid-Atlantic Ridge rises above the ocean surface in several places, forming islands. These islands include Ascension, the Azores, Iceland, and St. Helena.
Trenches form the deepest parts of the Atlantic.
A small number of trenches occur near the West Indies and off the southern tip of South America. The ocean depths The layers of water at the Atlantic's lowest depths are known as deep waters and bottom waters . They come from the surface and are the only source of oxygen for the life in the deep basin. Bottom waters range from a depth of about 13,100 feet to the seafloor. An important water mass, the Antarctic bottom waters, forms along the Antarctic coast, which has the world's coldest ocean waters.