Atlantic Ocean - Ocean Bottom

Ocean Bottom

The principal feature of the bathymetry (bottom topography) is a submarine mountain range called the Mid-Atlantic Ridge. It extends from Iceland in the north to approximately 58° South latitude, reaching a maximum width of about 860 nautical miles (1,590 km; 990 mi). A great rift valley also extends along the ridge over most of its length. The depth of water at the apex of the ridge is less than 2,700 metres (1,500 fathoms; 8,900 ft) in most places, while the bottom of the ridge is three times as deep. Several peaks rise above the water and form islands. The South Atlantic Ocean has an additional submarine ridge, the Walvis Ridge.

The Mid-Atlantic Ridge separates the Atlantic Ocean into two large troughs with depths from 3,700–5,500 metres (2,000–3,000 fathoms; 12,000–18,000 ft). Transverse ridges running between the continents and the Mid-Atlantic Ridge divide the ocean floor into numerous basins. Some of the larger basins are the Blake, Guiana, North American, Cape Verde, and Canaries basins in the North Atlantic. The largest South Atlantic basins are the Angola, Cape, Argentina, and Brazil basins.

The deep ocean floor is thought to be fairly flat with occasional deeps, abyssal plains, trenches, seamounts, basins, plateaus, canyons, and some guyots. Various shelves along the margins of the continents constitute about 11% of the bottom topography with few deep channels cut across the continental rise.

Ocean floor trenches and seamounts:

• Puerto Rico Trench, in the North Atlantic, is the deepest trench at 8,605 metres (4,705 fathoms; 28,230 ft)
• Laurentian Abyss is found off the eastern coast of Canada
• South Sandwich Trench reaches a depth of 8,428 metres (4,608 fathoms; 27,650 ft)
• Romanche Trench is located near the equator and reaches a depth of about 7,454 metres (4,076 fathoms; 24,460 ft).

Ocean sediments are composed of:

• Terrigenous deposits with land origins, consisting of sand, mud, and rock particles formed by erosion, weathering, and volcanic activity on land washed to sea. These materials are found mostly on the continental shelves and are thickest near large river mouths or off desert coasts.
• Pelagic deposits, which contain the remains of organisms that sink to the ocean floor, include red clays and Globigerina, pteropod, and siliceous oozes. Covering most of the ocean floor and ranging in thickness from 60–3,300 metres (33–1,800 fathoms; 200–11,000 ft) they are thickest in the convergence belts, notably at the Hamilton Ridge and in upwelling zones.
• Authigenic deposits consist of such materials as manganese nodules. They occur where sedimentation proceeds slowly or where currents sort the deposits, such as in the Hewett Curve.