Bathymetry

Arctic Ocean

continental shelf: The continental shelf (see Figure 1), a rather flat area of the sea floor adjacent to the coast that gradually slopes down from the shore to water depths that are typically less than 200 m (660 ft). Dimensions can vary: they may be narrow or nearly nonexistent in some places or extend for hundreds of miles in others. The waters above the continental shelf are usually productive in both plant and animal life, both from sunlight and nutrients from ocean upwelling and terrestrial runoff. More than one quarter of the Arctic sea floor is continental shelf. The Eurasian shelf is very wide, extending out 1,500 km (930 mi), and is the largest continental shelf in the world. The following are examples of features found on the continental shelf of the Arctic Ocean (see Figure 2).

Barents Shelf
Beaufort Shelf
Davis Sill
Chukchi Shelf
East Siberian Shelf
Kara Shelf
Laptev Shelf
Lincoln Shelf

continental slope: The continental slope (see Figure 1) is where the ocean bottom drops off more rapidly until it meets the deep-sea floor (abyssal plain) at depths exceeding 3,000 m (9,850 ft). The deep waters of the continental slope are characterized by cold temperatures, low light conditions, and very high pressures. Sunlight does not penetrate to these depths, having been absorbed or reflected in the water above. The continental slope can be indented by submarine canyons, often associated with the outflow of major rivers. Another feature of the continental slope is alluvial fans, or cones of sediments, that major rivers carry downstream to the ocean and deposit down the slope. The following are examples of features found on the continental slope of the Arctic Ocean (see Figure 2):

Litke Trough
Novaya Zemlya Trough
Svyataya Anna Trough (Saint Anna Trough)
Voronin Trough

abyssal plains: The abyssal plains (see Figure 1), at depths of over 3,000 m (10,000 ft) and covering 70% of the ocean floor, are the largest habitat on earth. Sunlight does not penetrate to the sea floor, making these deep, dark ecosystems less productive than those along the continental shelf. Despite their name, these “plains” are not uniformly flat; they are interrupted by features like hills, valleys, and seamounts. The following are examples of features found on the abyssal plains of the Arctic Ocean (see Figure 2):

Baffin Basin
Canada Basin
Fram/Amundsen Basin
Greenland Abyssal Plain
Iceland Basin
Makarov Basin
Molloy Deep; note - deepest point in the Arctic Ocean
Nansen Basin
Norwegian Basin

mid-ocean ridge: The mid-ocean ridge (see Figure 1) that rises from the abyssal plain is an underwater mountain range over 64,000 km (40,000 mi) long, reaching an average depth of 2,400 m (8,000 ft). Mid-ocean ridges form at divergent plate boundaries where two tectonic plates are moving apart and magma pushing up from the mantle creates new crust. Tracing their way around the global ocean, this system of underwater volcanoes forms the longest mountain range on Earth. Fracture zones are linear transform faults that develop perpendicular to the line of the mid-ocean ridge, which can offset the ridge line and divide it into segments. The following are examples of mid-ocean ridges found in the Arctic Ocean (see Figure 2):

Gakkel Ridge
Mohns Ridge

undersea terrain features:

The Abyssal Plain is commonly interrupted by a variety of undersea terrain features including seamounts, guyots, ridges, and plateaus.

Seamounts (see Figure 1) are submarine mountains at least 1,000 m (3,300 ft) high that are formed from individual volcanoes on the ocean floor. They are distinct from the plate-boundary volcanic system of the mid-ocean ridges because seamounts tend to be circular or conical. A circular-collapse caldera is often centered at the summit, evidence of a magma chamber within the volcano. "Hot spots" in the deep mantle often feed long chains of seamounts. These hot spots are associated with stationary plumes of molten rock rising from deep within the Earth's mantle. The hot-spot plumes melt through the overlying tectonic plate as it moves and supplies magma to the active volcanic island at the end of the chain of volcanic islands and seamounts.

Flat-topped seamounts are known as guyots. 

An undersea ridge is an elongated elevation of varying complexity and size, generally having steep sides.

An undersea plateau is a large, relatively flat elevation that is higher than the surrounding relief, with one or more relatively steep sides. Although submerged, these features can reach close to sea level.

The following are examples of undersea terrain features found on the floor of the Arctic Ocean (see Figure 2):

Lomonosov Ridge
Gakkel Ridge
Alpha Ridge
Mendeleev Rise
Chukchi Plateau

ocean trenches: there are no oceanic trenches on the Arctic sea floor

atolls: there are no atolls found in the Arctic Ocean

Atlantic Ocean

continental shelf: The continental shelf (see Figure 1), a rather flat area of the sea floor adjacent to the coast that gradually slopes down from the shore to water depths of about 200 m (660 ft). Dimensions can vary: they may be narrow or nearly nonexistent in some places or extend for hundreds of miles in others. The waters along the continental shelf are usually productive in both plant and animal life, both from sunlight and nutrients from ocean upwelling and terrestrial runoff. The passive margins of the Atlantic Ocean provide for wide continental shelves in North America, Northwest Europe, and the southern coast of South America. The following are examples of features found on the continental shelf of the Atlantic Ocean:

Blake Plateau (Figure 5)
Celtic Shelf (Figure 2)
Dogger Bank (Figure 2)
Flemish Cap (Figure 2)
Falkland Plateau (Figure 3)
Grand Banks of Newfoundland (Figure 2)
Great Bahama Bank (Figure 5)
Little Bahama Bank (Figure 5)
Tunisian Plateau (Figure 4)
Yucatán Shelf (Figure 5)

continental slope: The continental slope (see Figure 1) is where the ocean bottom drops off more rapidly until it meets the deep-sea floor (abyssal plain) at about 3,200 m (10,500 ft) water depth. The deep waters of the continental slope are characterized by cold temperatures, low light conditions, and very high pressures. Sunlight does not penetrate to these depths, having been absorbed or reflected in the water above. The continental slope can be indented by submarine canyons, which are often associated with the outflow of major rivers. Another feature of the continental slope is alluvial fans, or cones of sediments, that major rivers carry downstream to the ocean and deposit down the slope. The following are examples of features found on the continental slope of the Atlantic Ocean:

Amazon Cone (Figure 3)
Congo Fan (Figure 3)
Hudson Canyon (Figure 5)
Mississippi Fan (Figure 5)

abyssal plains: The abyssal plains (see Figure 1), at depths of over 3,000 m (10,000 ft) and covering 70% of the ocean floor, are the largest habitat on earth. Sunlight does not penetrate to the sea floor, making these deep, dark ecosystems less productive than those along the continental shelf. Despite their name, these “plains” are not uniformly flat; they are interrupted by features like hills, valleys, and seamounts. The following are examples of features found on the abyssal plains of the Atlantic Ocean:

Angola Basin (Figure 3)
Agulhas Basin (Figure 3)
Argentine Basin (Figure 3)
Brazil Basin (Figure 3)
Canary Basin (Figure 2)
Cape Basin (Figure 3)
Colombia Basin (Figure 2)
Labrador Basin (Figure 2)
Mexico Basin (Figure 2)
Newfoundland Basin (Figure 2)
North American Basin (Figure 2)
Venezuela Basin (Figure 2)
West European Basin (Figure 2)

mid-ocean ridge: The mid-ocean ridge (see Figure 1), rising from the abyssal plain, is an underwater mountain range, over 64,000 km (40,000 mi) long, reaching an average depth of 2,400 m (8,000 ft). Mid-ocean ridges form at divergent plate boundaries where two tectonic plates are moving apart and magma pushing up from the mantle creates new crust. Tracing their way around the global ocean, this system of underwater volcanoes forms the longest mountain range on Earth. Fracture zones are linear transform faults that develop perpendicular to the line of the mid-ocean ridge, which can offset the ridge line and divide it into segments. The Charlie-Gibbs Fracture Zone displaces the mid-ocean ridge 350 km to the west, separating the Mid-Atlantic Ridge from the Reykjanes Ridge. The Romanche Fracture Zone, located near the Equator, offsets the Mid-Atlantic Ridge 900 km and is considered the dividing line between the North and South Atlantic Oceans. The following are examples of mid-ocean ridges found on the floor of the Atlantic Ocean:

East Mediterranean Ridge (Figure 4)
Mid-Atlantic Ridge (Figures 2, 3)
Reykjanes Ridge (Figure 2)

undersea terrain features: The Abyssal Plain is commonly interrupted by a variety of commonly named undersea terrain features including seamounts, guyots, ridges, and plateaus.

Seamounts (see Figure 1) are submarine mountains at least 1,000 m (3,300 ft) high formed from individual volcanoes on the ocean floor. They are distinct from the plate-boundary volcanic system of the mid-ocean ridges, because seamounts tend to be circular or conical. A circular-collapse caldera is often centered at the summit, evidence of a magma chamber within the volcano. "Hot spots" in the deep mantle often feed long chains of seamounts. These hot spots are associated with stationary plumes of molten rock rising from deep within the Earth's mantle. The hot-spot plumes melt through the overlying tectonic plate as it moves and supplies magma to the active volcanic island at the end of the chain of volcanic islands and seamounts. 

Flat topped seamounts are known as guyots.

An undersea ridge is an elongated elevation of varying complexity and size, generally having steep sides.

An undersea plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides. Although submerged, these features can reach close to sea level. The following are examples of undersea terrain features found on the floor of the Atlantic Ocean:

Bermuda Rise (Figure 2)
Cape Verde Plateau (Figure 2)
New England Seamounts (Figure 2)
Rio Grande Plateau (Figure 3)
Rockall Plateau (Figure 2)

ocean trenches: Ocean trenches (see Figure 1) are the deepest parts of the ocean floor and are created by the process of subduction. Trenches form along boundaries where tectonic plates are moving toward each other, and one plate sinks (is subducted) under another. The location where the sinking of a plate occurs is called a subduction zone. Subduction can occur when oceanic crust collides with and sinks under (subducts) continental crust, resulting in volcanic, seismic, and mountain-building processes. Subduction can also occur in the convergence of two oceanic plates, where one will sink under the other and in the process create a deep ocean trench.

Subduction processes in oceanic-to-oceanic plate convergence also result in the formation of volcanoes. Over millions of years, the erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form a volcanic island. Such volcanoes are typically strung out in curved chains called island arcs. 

The following are examples of ocean trenches found on the floor of the Atlantic Ocean:

Cayman Trench (Caribbean Sea) (Figure 2)
Hellenic Trench (Mediterranean Sea) (Figure 4)
Puerto Rico Trench (Figure 2); note - deepest point in the Atlantic Ocean
South Sandwich Trench (South Atlantic) (Figure 3)

atolls: Atolls are the remains of dormant volcanic islands. In warm tropical oceans, coral colonies establish themselves on the margins of the island. Then, over time, the high elevation of the island collapses and erodes away to sea level, leaving behind an outline of the island in the form of the fringing coral reef. The resulting low island is typified by the coral reef that surrounds a low elevation of sand and coral, with an interior shallow lagoon. Often the remaining dry land is broken into a ring of islets, and some lagoons can be hundreds of square kilometers. 

Guyots are submerged atoll structures, which explains why they are flat-topped.

Rocas Atoll (Brazil) is the only atoll in the South Atlantic.

Indian Ocean

continental shelf:

The continental shelf (see Figure 1) is a rather flat area of the sea floor adjacent to the coast that gradually slopes from the shore to water depths of about 200 m (660 ft). Dimensions can vary: the shelves may be narrow or nearly nonexistent in some places or extend for hundreds of miles in others. The waters along the continental shelf are usually productive in both plant and animal life, from sunlight and nutrients from ocean upwelling and terrestrial runoff. The following are examples of features found on the continental shelf of the Indian Ocean (see Figure 2):

Exmouth Plateau
Indus Canyon
The Swatch of No Ground/Ganges Canyon (Bay of Bengal)
Sunda Shelf

continental slope:

The continental slope (see Figure 1) is where the ocean bottom drops off more rapidly until it meets the deep-sea floor (abyssal plain) at about 3,200 m (10,500 ft) water depth. The deep waters of the continental slope are characterized by cold temperatures, low light conditions, and very high pressures. Sunlight does not penetrate to these depths, having been absorbed or reflected in the water above. The continental slope can be indented by submarine canyons, often associated with the outflow of major rivers. Another feature of the continental slope is alluvial fans, or cones of sediments, that major rivers carry downstream to the ocean and deposit down the slope. The following are examples of features found on the continental slope of the Indian Ocean (see Figure 2):

Bengal Fan
Indus Fan

abyssal plains:

The abyssal plains (see Figure 1), at depths of over 3,000 m (10,000 ft) and covering 70% of the ocean floor, are the largest habitat on earth. Sunlight does not penetrate to the sea floor, making these deep, dark ecosystems less productive than those along the continental shelf. Despite their name, these “plains” are not uniformly flat; they are interrupted by features like hills, valleys, and seamounts. The following are examples of features found on the abyssal plains of the Indian Ocean (see Figure 2):

Arabian Basin
Crozet Basin
Madagascar Basin
Mid-Indian Basin
Mozambique Basin
Wharton Basin

mid-ocean ridge:

The mid-ocean ridge (see Figure 1), rising up from the abyssal plain, is an underwater mountain range over 64,000 km (40,000 mi) long, reaching an average depth of 2,400 m (8,000 ft). Mid-ocean ridges form at divergent plate boundaries where two tectonic plates are moving apart and magma pushing up from the mantle creates new crust. Tracing their way around the global ocean, this system of underwater volcanoes forms the longest mountain range on Earth. Fracture zones are linear transform faults that develop perpendicular to the line of the mid-ocean ridge, which can offset the ridge line and divide it into segments. The following are examples of mid-ocean ridges found on the floor of the Indian Ocean (see Figure 2):

Central Indian Ridge
Davie Ridge
Southeast Indian Ridge
Southwest Indian Ridge

undersea terrain features:

The Abyssal Plain is commonly interrupted by a variety of undersea terrain features including seamounts, guyots, ridges, and plateaus.

Seamounts (see Figure 1) are submarine mountains at least 1,000 m (3,300 ft) high formed from individual volcanoes on the ocean floor. They are distinct from the plate-boundary volcanic system of the mid-ocean ridges, because seamounts tend to be circular or conical. A circular collapse caldera is often centered at the summit, evidence of a magma chamber within the volcano. "Hot spots" in the deep mantle often feed long chains of seamounts. These hot spots are associated with stationary plumes of molten rock rising from deep within the Earth's mantle. The hot-spot plumes melt through the overlying tectonic plate as it moves and supplies magma to the active volcanic island at the end of the chain of volcanic islands and seamounts. 

Flat-topped seamounts are known as guyots.

An undersea ridge is an elongated elevation of varying complexity and size, generally having steep sides.

An undersea plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides. Although submerged, these features can reach close to sea level.

The following are examples of undersea terrain features found on the floor of the Indian Ocean (see Figure 2):

Andaman-Nicobar Ridge
Chagos-Laccadive Ridge
Kerguelen Plateau
Madagascar Plateau
Mascarene Plateau
Mozambique Plateau
Ninetyeast Ridge

ocean trenches:

Ocean trenches (see Figure 1) are the deepest parts of the ocean floor and are created by the process of subduction. Trenches form along convergent boundaries where tectonic plates are moving toward each other, and one plate sinks (is subducted) under another. The location where the sinking of a plate occurs is called a subduction zone. Subduction can occur when oceanic crust collides with and sinks under (subducts) continental crust, resulting in volcanic, seismic, and mountain-building processes. Subduction can also occur in the convergence of two oceanic plates, where one will sink under the other and in the process create a deep ocean trench.

Subduction processes in oceanic-to-oceanic plate convergence also result in the formation of volcanoes. Over millions of years, the erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form a volcanic island. Such volcanoes are typically strung out in curved chains called island arcs.

The following are examples of ocean trenches found on the floor of the Indian Ocean (see Figure 2):

Java/Sunda Trench; note - deepest point in the Indian Ocean

atolls:

Atolls (see Figure 1) are the remains of dormant volcanic islands. In warm tropical oceans, coral colonies establish themselves on the margins of the island. Then, over time, the high elevation of the island collapses and erodes away to sea level leaving behind an outline of the island in the form of the fringing coral reef. The resulting low island is typified by the coral reef that surrounds a low elevation of sand and coral above sea level, with an interior shallow lagoon. Often the remaining dry land is broken into a ring of islets, and some lagoons can be hundreds of square kilometers.

Guyots are submerged atoll structures, which explains why they are flat-topped seamounts.

The following are examples of atolls found in the Indian Ocean (see Figure 2):

Bassas da India
Chagos Archipelago/Diego Garcia
Europa Island
Juan de Nova Island
Lakshadweep Islands
Maldive Islands
Seychelles

Pacific Ocean

continental shelf: The continental shelf (see Figure 1), a rather flat area of the sea floor adjacent to the coast that gradually slopes down from the shore to water depths of about 200 m (660 ft). Dimensions can vary: they may be narrow or nearly nonexistent in some places or extend for hundreds of miles in others. The waters along the continental shelf are usually productive in both plant and animal life, from sunlight and nutrients from ocean upwelling and terrestrial runoff. The following are examples of features found on the continental shelf of the Pacific Ocean:

Arafura Shelf (Figure 5)
Sahul Shelf (Figure 5)
Sunda Shelf (Figure 5)
Taiwan Banks (Figure 5)

continental slope: The continental slope (see Figure 1) is where the ocean bottom drops off more rapidly until it meets the deep-sea floor (abyssal plain) at about 3,200 m (10,500 ft) water depth. The deep waters of the continental slope are characterized by cold temperatures, low light conditions, and very high pressures. Sunlight does not penetrate to these depths, having been absorbed or reflected in the water above. The continental slope can be indented by submarine canyons, often associated with the outflow of major rivers. Another feature of the continental slope is alluvial fans, or cones of sediments, that major rivers carry downstream to the ocean and deposit down the slope. The following are examples of features found on the continental slope of the Pacific Ocean:

Pribilof Canyon (Figure 2)
Zhemchug Canyon (Figure 2); note - deepest submarine canyon

abyssal plains: The abyssal plains (see Figure 1), at depths of over 3,000 m (10,000 ft) and covering 70% of the ocean floor, are the largest habitat on earth. Sunlight does not penetrate to the sea floor, making these deep, dark ecosystems less productive than those along the continental shelf. Despite their name, these “plains” are not uniformly flat; they are interrupted by features like hills, valleys, and seamounts. The following are examples of features found on the abyssal plains of the Pacific Ocean:

Aleutian Basin (Figure 2)
Central Pacific Basin (Figure 2)
Northeast Pacific Basin (Figure 2)
Northwest Pacific Basin (Figure 2)
Philippine Basin (Figure 4)
Southwest Pacific Basin (Figure 4)
Tasman Basin (Figure 4)

mid-ocean ridge: The mid-ocean ridge (see Figure 1), rising up from the abyssal plain, is an underwater mountain range over 64,000 km (40,000 mi) long, reaching an average depth of 2,400 m (8,000 ft). Mid-ocean ridges form at divergent plate boundaries where two tectonic plates are moving apart and magma  pushing up from the mantle creates new crust. Tracing their way around the global ocean, this system of underwater volcanoes forms the longest mountain range on earth. Fracture zones are linear transform faults that develop perpendicular to the line of the mid-ocean ridge, which can offset the ridge line and divide it into segments. The following are examples of mid-ocean ridges found on the floor of the Pacific Ocean:

East Pacific Rise (Figure 3)
Pacific-Antarctic Ridge (Figure 3)

undersea terrain features: The Abyssal Plain is commonly interrupted by a variety of commonly named undersea terrain features including seamounts, guyots, ridges, and plateaus.

Seamounts (see Figure 1) are submarine mountains at least 1,000 m (3,300 ft) high formed from individual volcanoes on the ocean floor. They are distinct from the plate-boundary volcanic system of the mid-ocean ridges, because seamounts tend to be circular or conical. A circular-collapse caldera is often centered at the summit, evidence of a magma chamber within the volcano. "Hot spots" in the deep mantle often feed long chains of seamounts. These hot spots are associated with stationary plumes of molten rock rising from deep within the Earth's mantle. The hot-spot plumes melt through the overlying tectonic plate as it moves and supplies magma to the active volcanic island at the end of the chain of volcanic islands and seamounts.

Flat topped seamounts are known as guyots.

An undersea ridge is an elongated elevation of varying complexity and size, generally having steep sides.

An undersea plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides. Although submerged, these features can reach close to sea level.

The following are examples of undersea terrain features found on the floor of the Pacific Ocean:

Caroline Seamounts (Figure 5)
East Mariana Ridge (Figure 4)
Emperor Seamount Chain (Figure 2)
Hawaiian Ridge (Figure 2)
Lord Howe Seamount Chain (Figure 4)
Louisville Ridge (Figure 4)
Kapingamarangi (Ontong-Java) Rise (Figure 5); note - largest submarine plateau
Macclesfield Bank (Figure 5)
Marshall Seamounts (Figure 2)
Magellan Seamounts (Figure 2)
Mid-Pacific Seamounts (Figure 2)
Reed Tablemount (Figure 5)
Shatsky Rise (Figure 2); note - third largest submarine plateau
Tonga-Kermadec Ridge (Figure 4)

ocean trenches: Ocean trenches (see Figure 1) are the deepest parts of the ocean floor and are created by the process of subduction. Trenches form along convergent boundaries where tectonic plates are moving toward each other, and one plate sinks (is subducted) under another. The location where the sinking of a plate occurs is called a subduction zone. Subduction can occur when oceanic crust collides with and sinks under (subducts) continental crust resulting in volcanic, seismic, and mountain-building processes. Subduction can also occur in the convergence of two oceanic plates, where one will sink under the other and in the process create a deep ocean trench.

Subduction processes in oceanic-to-oceanic plate convergence also result in the formation of volcanoes. Over millions of years, the erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form a volcanic island. Such volcanoes are typically strung out in curved chains called island arcs.

The following are examples of ocean trenches found on the floor of the Pacific Ocean:

Aleutian Trench (Figure 2)
Chile Trench (Figure 3)
Izu-Ogasawara Trench (Figure 2)
Japan Trench (Figure 2)
Kermadec Trench (Figure 3, 4)
Kuril-Kamchatka Trench (Figure 2)
Manus Trench (Figure 4)
Mariana Trench (Figure 2, 4); note - deepest ocean trench
Middle America Trench (Figure 3)
Nansei-Shoto Trench (Figure 5)
Palau Trench (Figure 2, 4)
Philippine Trench (Figure 4)
Peru-Chile Trench (Figure 3)
South New Hebrides Trench (Figure 4)
Tonga Trench (Figure 3, 4)
Yap Trench (Figure 2, 4)

atolls: Atolls are the remains of dormant volcanic islands. In warm tropical oceans, coral colonies establish themselves on the margins of the island. Then, over time, the high elevation of the island collapses and erodes away to sea level, leaving behind an outline of the island in the form of the fringing coral reef. The resulting low island is typified by the coral reef that surrounds a low elevation of sand and coral, with an interior shallow lagoon. Often the remaining dry land is broken into a ring of islets, and some lagoons can be hundreds of square kilometers. 

Guyots are submerged atoll structures, which explains why they are flat-topped seamounts.

The following are examples of atolls found in the Pacific Ocean, and because most of these are also countries or territories, they have entries in The World Factbook with additional information:

Federated States of Micronesia
French Polynesia
Kiribati
Marshall Islands
Midway Island
Tonga
Tuvalu
Vanuatu
Wake Island

Southern Ocean

continental shelf: The continental shelf (see Figure 1), a rather flat area of the sea floor adjacent to the coast that gradually slopes down from the shore to water depths of about 200 m (660 ft). Dimensions can vary: they may be narrow or nearly nonexistent in some places or extend for hundreds of miles in others. The waters along the continental shelf are usually productive in both plant and animal life, from sunlight and nutrients from ocean upwelling and terrestrial runoff. In Antarctica, the continental shelf is narrower and much deeper than in other oceans, and glacial action has deeply scoured it. The following are examples of features found on the continental shelf of the Southern Ocean (see Figure 2):

Astrid Ridge (see also Figure 4)
Belgrano Bank
Gunnerus Ridge (see also Figure 4)
Hayes Bank
Iselin Bank

continental slope: The continental slope (see Figure 1) is where the ocean bottom drops off until it meets the deep-sea floor (abyssal plain) at about 3,200 m (10,500 ft) water depth. The deep waters of the continental slope are characterized by cold temperatures, low light conditions, and very high pressures. Sunlight does not penetrate to these depths, having been absorbed or reflected in the water above. The continental slope can be indented by submarine canyons, which are often associated with the outflow of major rivers. Another feature of the continental slope is alluvial fans, or cones of sediments, that major rivers carry downstream to the ocean and deposit down the slope. In the case of Antarctica, glacial action has scoured the continental slope, cutting troughs and canyons. 

The following are examples of features found on the continental slope of the Southern Ocean (see Figure 2):

Amery Basin (see also Figure 4)
Filchner Trough
Hillary Canyon
Pobeda Canyon (Figure 3)

abyssal plains: The abyssal plains (see Figure 1), at depths of over 3,000 m (10,000 ft) and covering 70% of the ocean floor, are the largest habitat on earth. Sunlight does not penetrate to the sea floor, making these deep, dark ecosystems less productive than those along the continental shelf. Despite their name, these “plains” are not uniformly flat; they are interrupted by features like hills, valleys, and seamounts. The following are examples of features found on the abyssal plains of the Southern Ocean (see Figures 2, 3, and 4):

Amundsen (Abyssal) Plain
Enderby (Abyssal) Plain
South Indian/Australian-Antarctic Basin
Southeast Pacific/Bellinghausen Basin
Weddell (Abyssal) Plain

mid-ocean ridge: The mid-ocean ridge (see Figure 1), rising up from the abyssal plain, is an underwater mountain range, over 64,000 km (40,000 mi) long, reaching an average depth of 2,400 m (8,000 ft). Mid-ocean ridges form at divergent plate boundaries where two tectonic plates are moving apart and magma pushing up from the mantle creates new crust. Tracing their way around the global ocean, this system of underwater volcanoes forms the longest mountain range on earth. Fracture zones are linear transform faults that develop perpendicular to the line of the mid-ocean ridge, which can offset the ridge line and divide it into segments.

The following are examples of mid-ocean ridges found on the floor of the Southern Ocean (see Figure 2):

Pacific-Antarctic Ridge (see also Figure 3)

undersea terrain features: The abyssal plain is commonly interrupted by a variety of undersea terrain features including seamounts, guyots, ridges, and plateaus.

Seamounts (see Figure 1) are submarine mountains at least 1,000 m (3,300 ft) high formed from individual volcanoes on the ocean floor. They are distinct from the plate-boundary volcanic system of the mid-ocean ridges, because seamounts tend to be circular or conical. A circular-collapse caldera is often centered at the summit, evidence of a magma chamber within the volcano. "Hot spots" in the deep mantle often feed long chains of seamounts. These hot spots are associated with stationary plumes of molten rock rising from deep within the Earth's mantle. The hot-spot plumes melt through the overlying tectonic plate as it moves and supplies magma to the active volcanic island at the end of the chain of volcanic islands and seamounts. 

Flat topped seamounts are known as guyots.

An undersea ridge is an elongated elevation of varying complexity and size, generally having steep sides.

An undersea plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides. Although submerged, these features can reach close to sea level.

The following are examples of undersea terrain features found on the floor of the Southern Ocean (see Figure 2):

Akopov Seamounts (Figure 3)
De Gerlache Seamounts (see also Figure 3, 4)
Endurance Ridge (Figure 4)
Marie Byrd Seamount (see also Figure 3)
Maud Rise (see also Figure 4)
Scott Seamounts (see also Figure 3)

ocean trenches:

Ocean trenches (see Figure 1) are the deepest parts of the ocean floor and are created by the process of subduction. Trenches form along convergent boundaries where tectonic plates are moving toward each other, and one plate sinks (is subducted) under another. The location where the sinking of a plate occurs is called a subduction zone. Subduction can occur when oceanic crust collides with and sinks under (subducts) continental crust resulting in volcanic, seismic, and mountain-building processes. Subduction can also occur in the convergence of two oceanic plates where one will sink under the other and in the process create a deep ocean trench.

Subduction processes in oceanic-to-oceanic plate convergence also result in the formation of volcanoes. Over millions of years, the erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form a volcanic island. Such volcanoes are typically strung out in curved chains called island arcs.

The following are examples of ocean trenches found on the floor of the Southern Ocean (see Figure 2):

South Sandwich Trench (also see Figure 4); note - the deepest location in the Southern Ocean

atolls: due to the extremely cold water there are no atolls in the Southern Ocean