Bathymetry Southern Ocean, in 4 editions.

Rewritten: too little of the 2023 text remains to mark the changes.
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

Rewritten: too little of the 2024 text remains to mark the changes.
continental shelf: the following are examples of features 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 following are examples of features on the continental slope of the Southern Ocean (see Figure 2):
Amery Basin (Figure 4)
Filchner Trough
Hillary Canyon
Pobeda Canyon (Figure 3)
abyssal plains: the following are examples of features 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 following are examples of mid-ocean ridges on the floor of the Southern Ocean (see Figure 2):
Pacific-Antarctic Ridge (Figure 3)
undersea terrain features: the following are examples of undersea terrain features 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: the following are examples of ocean trenches on the floor of the Southern Ocean (see Figure 2):
South Sandwich Trench (Figure 4; the deepest location in the Southern Ocean)
atolls: none, due to the extremely cold water