Bathymetry:

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

Definition:

Bathymetry is the study of the depth and floors of bodies of water. This field describes the major bathymetric features found on the ocean floor. Specific bathymetric features associated with each of the following categories are listed for each ocean.

The continental shelf is 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). It is narrow or nearly nonexistent in some places; in others, it extends for hundreds of miles.

The continental slope is where the 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 continental slope can be indented by submarine canyons, often associated with the outflow of major rivers. Another feature of the continental slope are alluvial fans or cones of sediments carried downstream to the ocean by major rivers and deposited down the slope.

The abyssal plains, at depths of over 3,000 m (10,000 ft) and covering 70% of the ocean floor, are the largest habitat on earth. Despite their name, these “plains” are not uniformly flat and are interrupted by features like hills, valleys, and seamounts.

The mid-ocean ridge, rising up from the abyssal plain, is a continuous range of undersea volcanic mountains that encircles the globe almost entirely underwater. It is the longest mountain range on Earth at over 64,000 km (40,000 mi) long, rising to 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 creates new crust.

Seamounts 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. Flat-topped seamounts are known as "guyots."

Ocean trenches are the deepest parts of the ocean floor and are created by the process of subduction, when tectonic plates move toward each other and one plate sinks (is subducted) under another.

Atolls are the remains of dormant volcanic islands. In warm tropical oceans, coral colonies establish themselves on the margins of the island. 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 coral reef. The resulting island typically has a low elevation of sand and coral with an interior shallow lagoon.

Source: CIA World Factbook