Welcome to the Southern Ocean

The Southern Ocean covers 10 to 15 percent of the global ocean.

The temperature of the Southern Ocean ranges from 50°F (10°C) to 28°F (-2.2°C). 

The average depth of the Southern Ocean is roughly 11,000 feet (3,000 meters). 

Its deepest point is 23,740 feet (7,236 meters) at the southern end of the South Sandwich Trench.

The Antarctic Circumpolar Current is the longest, strongest, deepest-reaching current on earth.

The Southern Ocean plays an important role in regulating the global climate by absorbing heat and carbon dioxide from the atmosphere and driving global ocean circulation.

WELCOME TO THE SOUTHERN OCEAN

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Antarctic circumpolar current

Introduction

emperor penguin

Polar Front

stormy sea

Extremes

whale tail

Abundance

Spilhaus map of cool and warm currents

WELCOME TO THE SOUTHERN OCEAN

One global ocean

The ocean covers almost three quarters of our planet. While many of us think of the ocean as several separate bodies of water, there is only one global ocean. The global ocean is made up of five major ocean basins. Some water flows between them, and they all meet at the Southern Ocean.


Image credit: John Nelson

Southern ocean boundaries map
Southern Ocean boundaries. Image credit: apcpg

The Southern Ocean

Introduction

The Southern Ocean (also known as the Antarctic Ocean) is one of the five great ocean basins on Earth. It was formed around 34 million years ago when Antarctica and South America drifted apart, creating the Drake Passage. This makes it the youngest ocean basin on earth. 

Today, it is the only ocean that flows around the globe uninterrupted by land, encircling Antarctica like a moat. 

As the primary mixing zone between the world’s major oceans, the Southern Ocean plays an important role in the circulation of water around the globe. It also plays a key role in regulating the earth’s climate through its currents, seasonal sea ice and by absorbing heat and carbon dioxide from the atmosphere.

Antarctic circumpolar current
Image credit: Ceridwen Fraser

The Antarctic convergence

WHERE OCEANS MEET

Around the northern limit of the Southern Ocean there is a natural, biological boundary called the Antarctic Convergence, or Polar Front. 

North of the convergence, the water temperature near the surface sits at around 42.1°F (5.6 °C), ideal for marine species adapted to the subantarctic climate. South of the convergence, the water temperature drops dramatically to below 36 °F (2 °C), creating the perfect conditions for uniquely Antarctic wildlife to flourish.

Albatross
Albatross

Ocean oasis

WHERE OCEANS MEET

North of the Convergence the Southern Ocean meets the south Atlantic, Indian and Pacific Oceans. Here, the cold waters of the Southern Ocean mingle with the relatively warmer waters of the oceans to the north. Cold water from the south meets warmer water from the north, and because cold water is heavier, it sinks below. 

South of the Antarctic convergence there is also a zone of wind-driven upwelling, where water rises from the depths bringing nutrients to the surface. These nutrients act as a fertilizer for the ocean, and when they’re combined with sunlight, marine life flourishes. This makes the Antarctic convergence an area of great productivity, providing nourishment for a diversity of albatross, petrels and other seabirds.

Image credit: Commonwealth of Australia, Australian Antarctic Division

Fluid borders

WHERE OCEANS MEET

The exact location of the Antarctic convergence is difficult to pin down, as its watery boundaries are constantly in motion. It is between 20 and 30 miles (32 -48 km) wide, and ranges between roughly 45 and 60 degrees south. It tends to move seasonally, shifting north in the winter and south in the summer.

Although the convergence is always moving, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), which is responsible for the conservation of living species in the Southern Ocean, has defined its boundaries to help them regulate activities in these waters. The CAMLR Convention Area follows, as closely as possible, the biological limit of the Antarctic convergence.

stormy sea

CIRCULATION AND TRANSFORMATION

Extreme conditions

The Southern Ocean is known for its strong winds, intense storms, dramatic seasonal changes and cold temperatures. Each of these factors plays a role in the many important processes that occur in this part of the ocean, and help regulate the global climate.

Spilhaus map of Stipple Currents.
Image courtesy of John Nelson
Antarctic seasonal ice change.
Antarctic seasonal ice change. Image credit: NASA Goddard Space Flight Center Scientific Visualization Studio/ NASA Earth Observatory/ Jesse Allen

Strong currents 

THE SOUTHERN OCEAN

The Southern Ocean is dominated by the Antarctic Circumpolar Current (ACC): the longest, strongest, deepest-reaching current on earth. The ACC circulates clockwise around the continent, carrying more water around the globe than any other current. Learn more.

Frozen ocean

Each winter, Antarctica experiences one of the most remarkable seasonal changes on our planet. As temperatures plummet, the Southern Ocean freezes into a fringe of sea ice, almost doubling the size of Antarctica. Antarctica’s winter sea ice covers around 11 million miles (18 million sq.km), around twice the size of the United States of America. Learn more.

Phytoplankton bloom in Ross Sea_NASA Goddard

SUPPORTING LIFE

Abundant ecosystems

Virtually all the wildlife we associate with Antarctica, from tiny krill to the massive Antarctic blue whale, rely on the ocean and ice for their survival. 


Image credit: NASA Goddard

Emperor penguin diving
Emperor penguin
Antarctic krill
Antarctic krill (Euphausia superba)

One of the most productive ecosystems on earth

THE SOUTHERN OCEAN

Powerful currents, cold temperatures and nutrient and oxygen-rich waters make the Southern Ocean one of the most productive marine ecosystems on Earth. In summer billions of microscopic algae (phytoplankton) proliferate, spreading into blooms large enough to be seen from space. These single-celled marine plants provide nourishment for small invertebrates, shellfish, and Antarctic krill (Euphausia superba).

Antarctic krill are a keystone species within the Antarctic ecosystem. Grazing on the abundant algae of the Southern Ocean, hundreds of trillions of individual krill drift through the water column each summer. Like phytoplankton, their enormous swarms can be seen as pinkish patches from space. These small, shrimp-like crustaceans form the basis of many Antarctic marine animals’ diets, including penguins, seals and whales.

KEEP LEARNING

Related reading

iceshelf

Ocean pump

Antarctica helps regulate global ocean currents.

seal

Life on Ice

Reduced sea ice is impacting Antarctic life.

gentoo underwater

Acid seas

Carbon dioxide is making the ocean more acidic.

stormy sea

Ocean Heat

The Southern Ocean is warming up.

whale tail

Life at Sea

Warmer oceans are affecting ecosystems.

Now that you’ve learned about the Southern Ocean, read on to learn more about extraordinary Antarctica.

Southern Ocean

FEATURED LEARNING

humpback whale
Humpback whale
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