Southern Ocean

The Southern Ocean, also called the Antarctic Ocean, is the body of water that surrounds Antarctica and lies south of 60° S latitude. It is the second-smallest of the world’s five main oceans. It is smaller than the Pacific, Atlantic, and Indian Oceans, but larger than the Arctic Ocean.

In early February 2019, an expedition called the Five Deeps Expedition measured the deepest part of the Southern Ocean. They found it to be 7,434 metres (24,390 feet) deep. The leader of the expedition, Victor Vescovo, suggested calling this deepest spot the “Factorian Deep” after the submarine DSV Limiting Factor that first reached it.

For many years, people argued about whether the Southern Ocean should be considered a real, separate ocean. Finally, in 2000, a group of experts known as the International Hydrographic Organization decided yes, and defined the Southern Ocean as the waters south of a special ocean area where cold and warm waters meet, called the Antarctic Convergence.

The Southern Ocean plays a very important role in Earth’s climate. It helps move warm and cold water around the globe as part of a big system called the global thermohaline circulation. However, because of climate change, this system is changing. These changes could affect weather worldwide and the lives of animals and plants that live in the ocean.

Definition and term use

The International Hydrographic Organization's delineation of the "Southern Ocean" has moved steadily southward since the original 1928 edition of its Limits of Oceans and Seas.

The Southern Ocean, also called the Antarctic Ocean, is the body of water surrounding Antarctica. Its borders were agreed upon internationally in 1919 by the International Hydrographic Bureau. The waters south of the 60th parallel south are generally considered part of the Southern Ocean.

The National Geographic Society officially recognized the Southern Ocean in June 2021. Before that, its maps showed the Pacific, Atlantic, and Indian Oceans reaching toward Antarctica. Today, many maps and organizations use the term Southern Ocean for these southern waters.

History of exploration

Main article: History of Antarctica

People long believed in a large land far to the south, called Terra Australis, to balance the lands in the north. Early explorers like Bartolomeu Dias and Ferdinand Magellan began to see the cold southern waters and wondered about lands there.

The 1564 Typus Orbis Terrarum, a map by Abraham Ortelius, showed the imagined link between the proposed continent of Antarctica and South America.

Over time, explorers searched for this mysterious southern land. Some thought islands near Tierra del Fuego were part of it, but later journeys showed they were separate. Explorers like James Cook sailed far south, crossing the Antarctic Circle, but found only ice and no large land.

The first person to see land south of 60° S was William Smith, who spotted Livingston Island in 1819. Soon after, others saw parts of Antarctica’s icy coast. By the early 1800s, explorers had begun to uncover the edges of this hidden continent.

Antarctic expeditions

Main article: List of Antarctic expeditions

In the 1800s, many bold journeys explored Antarctica. One famous trip was led by James Clark Ross, who discovered a huge wall of ice now called the Ross Ice Shelf. Later, explorer Ernest Shackleton tried to cross Antarctica but had to survive on ice and boats.

In modern times, people have sailed, flown, and even rowed across the Southern Ocean. The area remains a place of wonder and discovery, protected by agreements that limit activities there to peaceful and scientific purposes.

Geography

The Southern Ocean is the youngest of the world's oceans. It formed when Antarctica and South America moved apart about 30 million years ago, creating the Drake Passage. This separation allowed the Antarctic Circumpolar Current to form.

The Southern Ocean is defined as the waters south of 60°S. Unlike other oceans, its northern boundary is shared with the Atlantic, Indian, and Pacific Oceans rather than touching land. The water in the Southern Ocean moves quickly due to the Antarctic Circumpolar Current, which flows around Antarctica.

The Southern Ocean is mostly deep, with depths between 4,000 and 5,000 meters. Its deepest point is 7,236 meters in the South Sandwich Trench. The area of ice around Antarctica changes with the seasons, growing from about 2.6 million square kilometers in March to 18.8 million square kilometers in September.

Subdivisions

The Southern Ocean has many parts such as seas, straits, and bays. Some of these include:

Biggest seas

Top large seas:

Natural resources

The Southern Ocean may hold large amounts of oil and gas. Valuable minerals, called placer deposits, might also be found there.

There may also be manganese nodules on the ocean floor. These are small rocks made of layers of iron and manganese. They have been of interest for mining in the past.

Each year, large icebergs form in the Southern Ocean. These icebergs contain enough fresh water to meet the needs of everyone on Earth for several months. There have been ideas to move these icebergs to drier areas, but none have succeeded yet.

Natural hazards

Icebergs can appear any time of year and can be very large. Smaller icebergs and sea ice can also be dangerous for ships.

The area between 40 degrees south and 70 degrees south is known for strong winds and big waves. These winds blow around the world without hitting land, creating rough seas. Icebergs make this area even more challenging for sailors. Because the region is so remote, help is hard to reach if needed.

Physical oceanography

Antarctic Circumpolar Current and Antarctic Convergence

The Southern Ocean is the second smallest ocean, but it has a special and very strong current called the Antarctic Circumpolar Current. This current moves eastward all the time and is the longest ocean current in the world. It carries a lot of water — enough to fill 130 million bathtubs every second!

Near Antarctica, special types of water form that are not found anywhere else. One is very cold and salty water that forms under sea ice. This meets warmer water from areas farther north in a place called the Antarctic Convergence. This mixing creates a lot of nutrients that help tiny plants called phytoplankton grow. These plants feed small animals like copepods and Antarctic krill, which in turn support fish, whales, seals, penguins, and many other animals.

The Antarctic Convergence is considered the best way to define where the Southern Ocean ends to the north.

Upwelling

The Southern Ocean has a lot of upwelling, where deep, cold water rises to the surface. Strong winds around Antarctica push water northward, which helps bring this deep water up. This upwelling is very important because it brings nutrients from the deep ocean to the surface, helping plants and animals grow.

Ross and Weddell gyres

There are two large circular movements of water in the Southern Ocean called the Ross Gyre and the Weddell Gyre. Both of these spin in a clockwise direction. They are formed by the way the Antarctic Circumpolar Current interacts with the land around Antarctica.

Because of the way wind and water move in the Southern Hemisphere, these areas are very good for growing plants and animals due to the upwelling of cold, nutrient-rich water.

Observation

Scientists study the Southern Ocean using the Southern Ocean Observing System (SOOS). This system collects important information about the ocean, such as water temperature and currents, especially for areas south of 40°S. This helps us understand how the ocean is changing.

Climate

The Southern Ocean has sea temperatures that range from about −2 to 10 °C (28 to 50 °F). Strong storms move eastward around Antarctica, often becoming very powerful because of the temperature difference between the ice and the open ocean. Between about latitude 40 south and the Antarctic Circle, this ocean has the strongest average winds found anywhere on Earth. In winter, the ocean can freeze out to 65 degrees south latitude in the Pacific area and 55 degrees south latitude in the Atlantic area, making surface temperatures drop well below 0 °C. In some coastal areas, strong winds from the land keep the shoreline free of ice all winter.

Biodiversity

Animals

The Southern Ocean is home to many marine animals that depend on phytoplankton. These include penguins like the emperor penguin and Adélie penguin, as well as large animals such as blue whales and orcas. The ocean’s ecosystem relies heavily on Antarctic krill, which are tiny creatures that feed many larger animals like whales, seals, and birds.

The seafloor also teems with life, from tiny creatures to larger animals. Some sea creatures grow to huge sizes due to the deep, cold waters.

A big study of sea life in polar regions found many species living in both the Arctic and Antarctic. Some small sea animals, like certain worms and snails, manage to live in both places, possibly helped by the cold, deep ocean waters and ocean currents.

Birds

Fish

The Southern Ocean does not have many fish species, but some families are more common. The snailfish are the most numerous, followed by cod icefish and eelpout. Many of these fish have special proteins in their bodies that keep them from freezing in the cold waters.

One interesting group is the icefish, which live in very cold water. Some icefish, called crocodile icefish, have blood that looks clear because they lack a certain substance that normally gives blood its colour. These fish spend their days on the seafloor and move higher in the water at night to feed.

There are also large fish called toothfish, which can grow very big. These fish are sometimes overfished, which has reduced their numbers.

Mammals

Invertebrates

Arthropods

Krill, tiny shrimp-like creatures, are one of the most common animals in the Southern Ocean. They form huge swarms and are an important food source for many larger animals. During the winter, krill can shrink in size to survive when food is hard to find.

The ocean floor has many different crabs and other small creatures. Some of these animals can grow quite large, and many different types of sea spiders live here too.

Molluscs, urchins, squid and sponges

The Southern Ocean has many different kinds of sea creatures with shells. Some of these, like the colossal squid, are among the largest invertebrates in the world. Squid are an important food source for many animals, including some birds and whales.

Sea urchins dig through the ocean floor to find food. There are also special creatures called salps that drift in the water. Sponges, which are very sensitive to changes in their environment, help scientists understand how healthy the ocean is.

Environment

More sunlight reaching the Southern Ocean because of a hole in the Earth's protective layer has made it harder for tiny plants in the water to grow and has hurt some fish.

There are special rules to protect animals and plants in the Southern Ocean. For example, there is a safe area where big whaling ships are not allowed to catch whales. Some countries disagree with these rules, but groups work together to make sure sea animals are safe and that fishing does not harm the ocean’s balance.

Economy

From July 1, 1998, to June 30, 1999, fishermen caught 119,898 tonnes of fish. Most of this catch was krill, with some being Patagonian toothfish. New rules started in late 1999 to stop people from catching fish without following the rules. These rules helped reduce the amount of fish caught illegally.

Ports and harbors

Major ports in the Southern Ocean include Rothera Station, Palmer Station, Villa Las Estrellas, Esperanza Base, Mawson Station, McMurdo Station, and some offshore anchorages in Antarctica.

Because of ice, most of the southern coast of the Southern Ocean can only be used for short periods in the middle of summer, and sometimes needs an icebreaker to reach it. Most ports here are run by government research stations and are usually closed to regular ships, except in emergencies. Ships south of 60 degrees south may be checked by observers from the Antarctic Treaty. The southernmost port is at McMurdo Station, where Winter Quarters Bay serves as a small harbor with a floating ice pier that allows ships to visit in summer. The first ice pier there was built in 1973 by Operation Deep Freeze workers.

Depending on how the Southern Ocean is defined, some ports in Australia, such as Albany, Thevenard, Port Lincoln, Whyalla, Port Augusta, Port Adelaide, Portland, Warrnambool, and Macquarie Harbour on the mainland and Tasmania, could also be considered part of the Southern Ocean.

Although some yacht races claim to go through the Southern Ocean, their routes usually stay within the South Atlantic, South Pacific, and Indian Ocean.