Southern Ocean

The great ocean surrounding Antarctica

Overview

The Southern Ocean is the ocean surrounding the continent of Antarctica. It forms a continuous body of water around the Antarctic continent and connects the Atlantic, Pacific and Indian Oceans.

It is the southernmost of Earth's five recognised oceans and is characterised by extremely cold waters, powerful winds, large waves, extensive seasonal sea ice and one of the most important ocean currents on Earth.

Key fact: The Antarctic Circumpolar Current flows continuously around Antarctica and links the Atlantic, Pacific and Indian Ocean basins.

Geography of the Southern Ocean

The Southern Ocean surrounds Antarctica and extends northward into the southern parts of the Atlantic, Pacific and Indian Ocean basins.

Unlike most of the world's oceans, the Southern Ocean is defined primarily by the circulation of water around Antarctica rather than by surrounding continental boundaries.

Major geographical features

Size and Depth

Property Approximate information
Area Approximately 20 million km², depending on the boundary definition used
Location Surrounding Antarctica
Hemisphere Southern Hemisphere
Major latitude boundary Often defined around 60° south
Deepest regions Several deep ocean basins and trenches occur around Antarctica

The exact area of the Southern Ocean varies according to the geographical definition used.

The Southern Ocean Seafloor

The seafloor beneath the Southern Ocean contains deep basins, submarine ridges, continental shelves, abyssal plains and trenches.

Important features include:

Major Seas of the Southern Ocean

Sea Location / significance
Weddell Sea Located east of the Antarctic Peninsula and adjacent to the Atlantic sector of Antarctica.
Ross Sea A large embayment of the Southern Ocean south of the Pacific Ocean.
Amundsen Sea Located along the coast of West Antarctica.
Bellingshausen Sea Located west of the Antarctic Peninsula.
Scotia Sea Situated between South America, the Antarctic Peninsula and several Southern Ocean island groups.

Antarctic Sea Ice

Sea ice is one of the most important physical characteristics of the Southern Ocean.

Unlike the Antarctic Ice Sheet, which is land-based, sea ice forms when seawater freezes and floats on the ocean surface.

Seasonal cycle

Antarctic sea ice generally reaches its greatest extent during the Southern Hemisphere winter and its smallest extent during late summer.

Important distinction: Antarctic sea ice is frozen seawater, whereas the Antarctic Ice Sheet is frozen freshwater accumulated on land.

Icebergs

The Southern Ocean contains some of the world's largest icebergs.

Icebergs are pieces of freshwater ice that have broken away from glaciers or ice shelves in a process known as calving.

They can drift for hundreds or even thousands of kilometres before melting or becoming grounded.

Antarctic Ice Shelves

Ice shelves are floating extensions of the Antarctic Ice Sheet. They form where land-based glacial ice flows from Antarctica onto the ocean.

Major Antarctic ice shelves include:

The Antarctic Circumpolar Current

The Antarctic Circumpolar Current, or ACC, is the dominant ocean current of the Southern Ocean.

It flows from west to east around Antarctica and is the only major ocean current that completely circles a continent.

The current is driven primarily by the powerful westerly winds of the Southern Ocean.

Global importance: The Antarctic Circumpolar Current acts as a major connection between the Atlantic, Pacific and Indian Oceans.

Westerly Winds

Strong westerly winds dominate much of the Southern Ocean.

These winds are especially persistent because there is a broad belt of ocean surrounding Antarctica without major continents interrupting the atmospheric circulation.

The region is consequently famous for strong winds and rough seas.

Ocean Circulation

The Southern Ocean is a major component of global ocean circulation.

Cold, dense Antarctic waters can sink into the deep ocean and contribute to the formation of deep and bottom waters.

These waters can subsequently spread through the world's ocean basins.

Climate of the Southern Ocean

The Southern Ocean has one of the harshest marine climates on Earth.

Major characteristics include:

The Roaring Forties

The Roaring Forties are a belt of strong westerly winds found approximately between 40° and 50° south latitude.

These winds are particularly strong over the Southern Ocean because there are relatively few large landmasses to interrupt the flow.

The Furious Fifties

The Furious Fifties are a region of strong westerly winds farther south, roughly between 50° and 60° south latitude.

Winds and waves can be particularly severe in this region.

The Screaming Sixties

The Screaming Sixties refer to the powerful winds found around the higher southern latitudes near Antarctica.

Together, the Roaring Forties, Furious Fifties and Screaming Sixties illustrate the exceptionally energetic atmospheric environment of the Southern Ocean.

Wildlife of the Southern Ocean

The Southern Ocean supports a highly productive marine ecosystem.

Important animals include:

Antarctic Krill

Antarctic krill are small crustaceans that form one of the foundations of the Southern Ocean food web.

Large quantities of krill provide food for whales, seals, penguins, fish and seabirds.

Food-web importance: Antarctic krill provide an important link between microscopic primary producers and large marine predators.

Penguins

Several species of penguin are associated with the Antarctic region and Southern Ocean.

Important species include:

Emperor Penguins

Emperor penguins are the largest penguin species.

They are uniquely adapted to the Antarctic environment and breed during the Antarctic winter.

Their ability to survive extreme cold and prolonged darkness makes them one of the most remarkable animals of the Southern Ocean region.

Antarctic Seals

The Southern Ocean supports several species of seal.

Whales of the Southern Ocean

The Southern Ocean is an important feeding area for many whale species.

Many whales migrate between Antarctic feeding grounds and warmer waters at lower latitudes.

Albatrosses and Seabirds

The Southern Ocean is one of the world's most important environments for seabirds.

Albatrosses are especially well adapted to the region. Their enormous wings allow them to travel great distances using dynamic soaring over the ocean.

Other important seabirds include petrels, skuas and shearwaters.

Marine Food Web

Phytoplankton form the foundation of much of the Southern Ocean marine food web.

Phytoplankton are consumed by zooplankton and krill. Krill are then eaten by fish, penguins, seals, seabirds and whales.

Simple food chain:

Phytoplankton → Krill → Fish / Penguins / Seals → Whales and other predators

The Southern Ocean and Antarctica

The Southern Ocean completely surrounds Antarctica and plays a major role in the physical and biological environment of the continent.

The ocean transports heat towards and away from Antarctica, interacts with floating ice shelves and provides habitat for Antarctic marine life.

Antarctica and the Global Climate System

Antarctica and the Southern Ocean form a closely coupled climate system.

The Antarctic Ice Sheet stores enormous quantities of frozen freshwater, while the Southern Ocean absorbs heat and carbon dioxide from the atmosphere.

Changes in either the ocean or the ice sheet can therefore have consequences for the global climate system.

Southern Ocean Carbon Cycle

The Southern Ocean is an important region for the exchange of carbon dioxide between the atmosphere and the ocean.

Marine organisms absorb carbon dioxide through photosynthesis, while physical processes transport carbon into deeper layers of the ocean.

This makes the Southern Ocean an important component of the global carbon cycle.

Exploration of the Southern Ocean

The Southern Ocean has been explored by navigators, explorers, scientists and Antarctic expeditions for centuries.

Important figures include:

James Cook

Captain James Cook made important voyages through the southern oceans during the eighteenth century.

His expeditions demonstrated that Antarctica was not a temperate southern continent easily accessible from lower latitudes and contributed substantially to geographical knowledge of the Southern Ocean.

James Clark Ross

James Clark Ross led major British Antarctic expeditions in the nineteenth century.

His expeditions investigated Antarctic waters and discovered important geographical features, including the Ross Sea and Ross Ice Shelf region.

Ernest Shackleton

Ernest Shackleton became one of the most famous explorers of the Antarctic region.

His Endurance expedition demonstrated the extraordinary difficulties of operating ships in the ice-covered Southern Ocean.

Modern Scientific Research

Modern research in the Southern Ocean uses research vessels, autonomous instruments, satellites, aircraft, underwater vehicles and oceanographic moorings.

Scientists investigate:

Antarctic Circumpolar Current and Climate

The Antarctic Circumpolar Current is fundamental to the isolation of Antarctica from warmer subtropical waters.

By circulating around Antarctica, it provides an important barrier to the direct northward transport of warm surface waters.

It is therefore a major feature of the Southern Hemisphere climate system.

Environmental Change

The Southern Ocean is undergoing significant environmental change associated with global warming and other human influences.

Important environmental issues include:

Ocean Warming

The Southern Ocean absorbs a substantial amount of the excess heat associated with anthropogenic global warming.

Changes in ocean temperature can affect sea ice, marine ecosystems and the stability of Antarctic ice shelves.

Ocean Acidification

Increasing concentrations of atmospheric carbon dioxide lead to increased absorption of carbon dioxide by seawater.

This process causes ocean acidification, which can affect organisms that form shells or skeletons from calcium carbonate.

Fishing in the Southern Ocean

Commercial and scientific fisheries operate in parts of the Southern Ocean.

Important species and resources include Antarctic toothfish, Patagonian toothfish and Antarctic krill.

International management is important because Southern Ocean ecosystems are highly interconnected.

Conservation

The Southern Ocean contains some of the most remote and relatively undisturbed marine ecosystems on Earth.

Conservation measures include marine protected areas, fishing regulations, scientific monitoring and international cooperation.

Southern Ocean and the Five Oceans

Ocean Principal region
Pacific Ocean Between Asia/Oceania and the Americas
Atlantic Ocean Between the Americas and Europe/Africa
Indian Ocean Between Africa, Asia and Australia
Arctic Ocean Around the North Pole
Southern Ocean Around Antarctica

Southern Ocean and the Other Oceans

The Southern Ocean is unusual because it connects three of the world's major ocean basins through the Antarctic Circumpolar Current.

Water can circulate between the Atlantic, Pacific and Indian Oceans through the Southern Ocean.

Global connection: The Southern Ocean is a major junction in the planetary ocean circulation system.

Southern Ocean Timeline

Millions of years ago

Continental movements progressively established the geography of Antarctica and the surrounding oceans.

Opening of the Drake Passage

The development of an ocean connection between South America and Antarctica allowed a circumpolar ocean circulation to develop.

18th century

European voyages substantially increased geographical knowledge of the southern oceans.

19th century

Antarctic exploration expanded through expeditions led by James Clark Ross and others.

20th century

Antarctic scientific research became increasingly international and systematic.

21st century

Satellites, autonomous instruments and advanced oceanographic models have transformed understanding of the Southern Ocean.

Quick Facts About the Southern Ocean

Feature Information
Name Southern Ocean
Location Surrounding Antarctica
Hemisphere Southern Hemisphere
Common northern boundary Approximately 60° S
Approximate area About 20 million km²
Major current Antarctic Circumpolar Current
Major seas Weddell Sea, Ross Sea, Amundsen Sea, Bellingshausen Sea and Scotia Sea
Major wildlife Krill, penguins, seals, whales and seabirds
Major environmental feature Seasonal Antarctic sea ice
Major landmass Antarctica
Climate significance Major component of global ocean circulation and carbon cycling

Conclusion

The Southern Ocean is one of the most important components of Earth's ocean system. Surrounding Antarctica, it links the Atlantic, Pacific and Indian Oceans and supports a remarkable polar ecosystem.

Its Antarctic Circumpolar Current, sea ice, deep-water formation and exchange of heat and carbon with the atmosphere give it an influence that extends far beyond the Southern Hemisphere.

The Southern Ocean is therefore important not only as a geographical feature surrounding Antarctica, but also as a fundamental part of Earth's climate system and global circulation of the oceans.