Southern Ocean

• 1. Introduction

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  The deepest point of the Southern Ocean was not measured until early February 2019. The Five Deeps Expedition's multibeam sonar team fixed it at 7434 metres, at 60 degrees 28 minutes south, just below the 60th parallel. Expedition leader Victor Vescovo, who was also its chief submersible pilot, took the crewed submersible DSV Limiting Factor down to that floor on the 3rd of February 2019. Nobody had been there before. He has proposed naming the spot the Factorian Deep, after his vessel.

  The Southern Ocean surrounds Antarctica and covers 21,960,000 square kilometres. It is the second-smallest of the five principal oceanic divisions, larger only than the Arctic. Yet atlases argued for generations over whether it deserved to be called an ocean at all. Who decides where one ocean ends and another begins? Why did an official publication drop it in 1953? And what is it about this water that convinced oceanographers to demand it back?

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• 2. A Border Nobody Agreed On

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  Vasco Núñez de Balboa, the first European to discover the Pacific, approached it from the north, from Panama, and called it the Southern Ocean. For a long time that name simply meant the Pacific, or the South Pacific. "South Seas" is a less archaic synonym. A 1745 British Act of Parliament offered a prize for finding a Northwest Passage to "the Western and Southern Ocean of America".

  In 1795, Peacock's Geographical Dictionary placed a Southern Ocean to the southward of America and Africa. Later writers applied the name to the waters around the unexplored polar south, and each gave it different edges. John Payne in 1796 set its northern limit at 40 degrees, and the 1827 Edinburgh Gazetteer chose 50 degrees. James Cook's account of his second voyage implies that New Caledonia borders it.

  In 1835, the Family Magazine split a "Great Southern Ocean" in two along the Antarctic Circle, creating a Southern Ocean and an "Antarctick Ocean". The northern edge of the Southern Ocean followed lines joining Cape Horn, the Cape of Good Hope, Van Diemen's Land and the south of New Zealand. Lawmakers used the phrase as well. The South Australia Act 1834 described the "Southern Ocean" as the southern limit of the new province. Victoria's Legislative Council Act 1881 ran part of the Bairnsdale division's boundary "to the Southern ocean". That patchwork was still the norm when the International Hydrographic Bureau convened its First International Conference on the 24th of July 1919 to agree on borders and names.

  In 1928, the first edition of the Limits of Oceans and Seas drew the Southern Ocean using land alone. Antarctica lay to the south, and South America, Africa, Australia and Broughton Island in New Zealand lay to the north. The line ran from Cape Horn in Chile east to Cape Agulhas in Africa, then on to Cape Leeuwin in Western Australia. It followed the Australian coast to Cape Otway and crossed Bass Strait by way of King Island to Cape Grim in Tasmania. From there it ran down Tasmania's west coast to South East Cape and then east to Broughton Island.

  The 1937 second edition pushed the boundary south, and most of the northern edge no longer touched any coast. The ocean now reached 40 degrees south between Cape Agulhas at 20 degrees east and Cape Leeuwin at 115 degrees east. Between Auckland Island and Cape Horn at 67 degrees west, it reached 55 degrees south.

  In 1953, the third edition left the Southern Ocean out entirely, and a printed note explained why. Most opinions received since 1937, it said, held that calling the water an ocean had no real justification, because its northern limits shift with the seasons. The Atlantic, Pacific and Indian oceans were stretched south to the Antarctic continent instead. Offices that published their own works on the region were left to choose their northern limits. Great Britain used 55 degrees south.

  In 2000, the International Hydrographic Organization polled its 68 member nations on whether to revive the ocean. Only 28 replied, and every one of them except Argentina agreed it should be redefined, reflecting how much oceanographers value ocean currents. The name Southern Ocean won 18 votes, beating Antarctic Ocean. Half the votes backed a northern limit at the 60th parallel south. The other 14 went to other definitions, mostly the 50th parallel south, with a few as far north as the 35th.

  A draft fourth edition went out to member states in August 2002, yet it has never been published. Several countries raised concerns over naming issues, chiefly the dispute over the name of the Sea of Japan. The draft gave 60 seas new names, and Australia lodged a reservation about the Southern Ocean limits. The draft also treats seas as parts of oceans, so the Tasman Sea, once kept apart, now counts as Pacific. The 1953 edition therefore remains formally in force. Even so, the CIA World Factbook and Merriam-Webster use the draft's definition, as do some within the organization itself.

  Encyclopædia Britannica extends the Southern Ocean as far north as South America, yet its Indian Ocean entry runs that ocean south to Antarctica. The National Geographic Society once printed the Pacific, Atlantic and Indian oceans reaching Antarctica, and set the Southern Ocean in a different typeface. It recognized the ocean officially in June 2021.

  Australian authorities count all the water between Antarctica and the south coasts of Australia and New Zealand, and up to 60 degrees south elsewhere. Their maps treat Cape Leeuwin in Western Australia as the place where the Indian and Southern oceans meet.

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• 3. The Missing Continent

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  Since the time of Ptolemy, geographers had imagined a vast Terra Australis in the far south, needed to balance the northern masses of Eurasia and North Africa. In 1487, Bartolomeu Dias rounded the Cape of Good Hope and brought explorers within reach of Antarctic cold. His voyage showed that an ocean separated Africa from any such land. Ferdinand Magellan, passing through his strait in 1520, took the islands of Tierra del Fuego for part of the continent.

  In 1564, Abraham Ortelius published his first map, an eight-leaved wall map of the world called Typus Orbis Terrarum. It showed the Regio Patalis with Locach as a northward extension of Terra Australis, reaching as far as New Guinea. Other European geographers kept linking Tierra del Fuego with New Guinea on their globes. They let their imaginations fill the empty south with a continent they labelled Terra Australis Incognita, the "Unknown Southern Land". The hunt for it was a leading motive for explorers in the 16th and early 17th centuries.

  In 1603, the Spaniard Gabriel de Castilla claimed to have sighted "snow-covered mountains" beyond 64 degrees south. He is now recognized as the first explorer to discover Antarctica, though his own age ignored him. In 1606, Pedro Fernández de Quirós claimed for the king of Spain all the lands he had found in Australia del Espiritu Santo, the New Hebrides, and those he would find "even to the Pole".

  Francis Drake had speculated about an open channel south of Tierra del Fuego. In 1615, Willem Schouten and Jacob Le Maire found the archipelago's southern tip and named it Cape Horn. They proved the islands were small and not joined to any southern land. In 1642, Abel Tasman showed that even New Holland, meaning Australia, was separated by sea from any continuous southern continent.

  In 1675, Anthony de la Roché visited South Georgia, the first land ever found south of the Antarctic Convergence, a boundary zone of cold polar water. Cartographers soon drew it as "Roché Island". In January 1700, Edmond Halley, sailing HMS Paramour on a magnetic survey of the South Atlantic, met pack ice at 52 degrees south. That was his farthest south, about 140 miles off South Georgia's north coast.

  The French naval officer Jean-Baptiste Charles Bouvet de Lozier went looking for the "South Land" described by a half legendary "sieur de Gonneyville". He found Bouvet Island at 54 degrees 10 minutes south. In 1730 he navigated 48 degrees of longitude of ice-choked sea near 55 degrees south. In 1771, Yves Joseph Kerguelen sailed from France with orders to head south from Mauritius in search of "a very large continent". At 50 degrees south he found land he called South France and took for the heart of that continent. Sent back to finish exploring it, he found only an inhospitable island and renamed it the Isle of Desolation. It now carries his name.

  Alexander Dalrymple, a brilliant and erratic hydrographer, embodied the obsession. The Royal Society nominated him to command the 1769 Transit of Venus expedition to Tahiti, but the Admiralty gave the command to Captain James Cook. Sailing in 1772, Cook took Resolution, a vessel of 462 tons, with Adventure, 336 tons, under Captain Tobias Furneaux. Cook pushed south of 60 degrees south, a lower latitude than any vessel had voluntarily entered before. On the 17th of January 1773 the ships crossed the Antarctic Circle, the first crossing in history. They reached 67 degrees 15 minutes south before ice stopped them.

  Cook crossed the circle again on the 20th of December 1773 and stayed south of it for three days. After a long detour to 47 degrees 50 minutes south, which showed there was no land link between New Zealand and Tierra del Fuego, he crossed it a third time at 109 degrees 30 minutes west. Four days later, on the 30th of January 1774, ice blocked him at 71 degrees 10 minutes south. That was the farthest south reached in the 18th century.

  On the 29th of December 1774, Cook passed Cape Horn. He rediscovered Roché Island and renamed it the Isle of Georgia, then found the South Sandwich Islands, which he called Sandwich Land. They were the only ice-clad land he saw. His voyages exploded the myth of a habitable southern continent. He convinced himself that any land farther south would be practically inaccessible and worthless economically. Even his most southerly landfall lay on the temperate side of the 60th parallel, so the first land beyond it was still waiting to be found.

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• 4. Ice, Wrecks and Firsts

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  On the 19th of February 1819, the Englishman William Smith sighted Livingston Island, the first land found south of the 60th parallel south. A few months later he returned, landed on King George Island, and claimed the South Shetlands archipelago for Britain. In September 1819 the Spanish Navy ship San Telmo sank while trying to cross Cape Horn. Sealers found parts of her wreckage on the north coast of Livingston Island months later. Whether a survivor reached those shores first is unknown.

  Who first saw mainland Antarctica cannot be pinned on a single person. Three men sighted the ice shelf or continent within days or months of each other. Fabian Gottlieb von Bellingshausen, a captain in the Russian Imperial Navy, led the ships Vostok and Mirny with Lazarev. They came within 32 kilometres of Princess Martha Coast and recorded an ice shelf later known as the Fimbul Ice Shelf. On the 30th of January 1820, Edward Bransfield, a captain in the Royal Navy, sighted Trinity Peninsula, the northernmost point of the mainland. In November 1820, Nathaniel Palmer, an American sailor out of Stonington, Connecticut, sighted the mainland south of that peninsula. Bellingshausen's expedition also found Peter I Island and Alexander I Island, the first islands discovered south of the circle.

  From 1822 to 1824, James Weddell commanded the 160-ton brig Jane, accompanied by a second ship, Beaufoy, captained by Matthew Brisbane. Sealing at the South Orkneys disappointed them, so they turned south hoping for better grounds. The season was unusually mild and tranquil. On the 20th of February 1823 they reached 74 degrees 15 minutes south, farther south than any ship had ever been. A few icebergs and no land led Weddell to theorize that the sea continued all the way to the South Pole. Two more days' sailing would have brought him to Coat's Land, but he turned back.

  In December 1839, an American squadron sailed from Sydney as part of the United States Exploring Expedition of 1838-42, sometimes called the Wilkes Expedition. Its vessels included the sloops-of-war Vincennes and Peacock, the brig Porpoise, the ship Relief and two schooners. On the 25th of January 1840 they reported an Antarctic continent west of the Balleny Islands. That stretch of coast is still called Wilkes Land. In 1841, James Clark Ross passed through the sea that now bears his name and discovered Ross Island. He sailed along an immense wall of ice, later named the Ross Ice Shelf. His ships HMS Erebus and HMS Terror gave their names to Mount Erebus and Mount Terror.

  In 1914, Ernest Shackleton's Imperial Trans-Antarctic Expedition set out to cross the continent via the pole. Their ship Endurance was trapped and crushed by pack ice before they ever landed. The men survived an epic journey by sledge over the pack ice to Elephant Island. Shackleton and five others then crossed the Southern Ocean in an open boat, the James Caird. They trekked over South Georgia to raise the alarm at the whaling station at Grytviken.

  In 1946, US Navy Rear Admiral Richard E. Byrd led more than 4,700 military personnel south in Operation Highjump. The public was told it was a scientific mission, but the details stayed secret, and it may have been a training or testing exercise. It carried an aircraft carrier, submarines, assault troops and military vehicles. Planned to last eight months, it ended after two. Apart from some eccentric entries in Byrd's diaries, no official explanation has ever been given.

  Captain Finn Ronne, Byrd's executive officer, returned in 1947-1948 with his own expedition, backed by the Navy, with three planes and dogs. He disproved the idea that the continent was split in two, showing that the Weddell Sea and the Ross Sea are not connected. He mapped large parts of Palmer Land and the Weddell Sea coastline, and named the Ronne Ice Shelf for his wife Jackie Ronne. He covered 3600 miles by ski and dog sled, more than any other explorer. His was the first Antarctic expedition to include women, and it mapped the last unknown coastline in the world.

  The Antarctic Treaty was signed on the 1st of December 1959 and came into force on the 23rd of June 1961. It limits military activity in the Antarctic to supporting scientific research. In 1972, the New Zealander David Henry Lewis became the first person to sail single-handed to Antarctica, in a 10 metre steel sloop named Ice Bird. A baby named Emilio Marcos de Palma was born near Hope Bay on the 7th of January 1978. He was the first baby born on the continent, and born farther south than anyone in history.

  The Swedish explorer Lars-Eric Lindblad operated the cruise ship MV Explorer. Observers point to her 1969 expedition cruise to Antarctica as the forerunner of today's sea-based tourism there. She was the first cruise ship used specifically to sail these icy waters, and the first to sink in them. On the 23rd of November 2007 she struck an unidentified submerged object, reported to be ice, which opened a gash 10 by 4 inches in her hull. The sea near the South Shetland Islands is usually stormy, but it was calm. She was abandoned in the early hours, and the Chilean Navy confirmed she sank at about 62 degrees 24 minutes south, 57 degrees 16 minutes west, in roughly 600 metres of water.

  In 2019, the ocean saw two more firsts. British engineer Richard Jenkins designed an unmanned saildrone that completed the first autonomous circumnavigation of the Southern Ocean on the 3rd of August, after 196 days at sea. On the 25th of December 2019, a team of rowers completed the first fully human-powered expedition on the ocean. Its captain was Fiann Paul of Iceland, and its first mate was Colin O'Brady of the United States. The crew also included Andrew Towne, Cameron Bellamy of South Africa, Jamie Douglas-Hamilton of the United Kingdom, and John Petersen.

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• 5. The Current That Circles

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  Roughly 30 million years ago, Antarctica and South America moved apart and opened the Drake Passage. That made the Southern Ocean geologically the youngest of the oceans. The opening let the Antarctic Circumpolar Current form, and that current runs eastward without pause, chasing and joining its own tail. At 21,000 kilometres, it is the longest ocean current in the world. It carries 130 million cubic metres of water every second, which is 100 times the flow of all the world's rivers.

  Water south of New Zealand resembles water south of South America more closely than it resembles the Pacific water to its north. The current moves water around Antarctica quickly enough to blur the differences between sectors. That is one reason oceanographers want to treat the region as an ocean of its own. Its 60 degrees south northern edge is also unusual. Unlike the 1928 line, it meets no land, only the Atlantic, Indian and Pacific oceans.

  Typical depths run between 4,000 and 5,000 metres across most of the ocean, with only limited shallow areas. The Antarctic continental shelf is narrow and unusually deep, its edge lying at depths of up to 800 metres. The global mean is 133 metres. The ice pack breathes with the seasons. From equinox to equinox it swells from an average minimum of 2.6 million square kilometres in March to about 18.8 million in September, more than a sevenfold increase.

  Sailors call the latitudes from 40 to 70 degrees south the Roaring Forties, Furious Fifties and Shrieking Sixties. Winds and waves circle the globe here with no land to stop them. From about 40 degrees south to the Antarctic Circle, the average winds are the strongest found anywhere on Earth. Cyclonic storms travel eastward around the continent and often grow intense because of the contrast between ice and open water. Sea temperatures range from about -2 to 10 degrees Celsius, or 28 to 50 degrees Fahrenheit. In winter the ocean freezes outward to 65 degrees south in the Pacific sector and 55 degrees south in the Atlantic sector. At some coastal points, persistent drainage winds from the interior keep the shoreline ice-free all winter.

  Icebergs can appear in any month, and some have drafts of several hundred metres. Smaller bergs, fragments and sea ice, generally 0.5 to 1 metre thick, also trouble ships. The danger rises between May and October. The deep continental shelf has a floor of glacial deposits that varies widely over short distances. The remoteness of the region means search and rescue resources are scarce.

  Antarctic Bottom Water forms under sea ice along the coast, and it is very cold, very salty and dense. Processes there create water masses found nowhere else in the oceans of the Southern Hemisphere. Circumpolar Deep Water is another, a mixture of Antarctic Bottom Water and North Atlantic Deep Water.

  The Southern Ocean overturning circulation makes up the second half of the global thermohaline circulation, after the better known Atlantic meridional overturning circulation, or AMOC. Climate change has already increased ocean stratification here. The circulation may slow substantially, or even pass a tipping point and collapse outright. A collapse would unfold over centuries and would harm global weather and marine ecosystems, which are already changing.

  Strong westerly winds blow around Antarctica and drive a flow of water northward. Because no continents block the open latitudes between South America and the tip of the Antarctic Peninsula, some of that water is drawn up from great depths. In many models and observational syntheses, this upwelling is the main way deep dense water reaches the surface. The Ross Gyre and Weddell Gyre sit in the Ross Sea and Weddell Sea, and both rotate clockwise. They form where the circumpolar current interacts with the continental shelf. Sea ice persists in the centre of the Ross Gyre, and there is some evidence that warming has lowered its salinity since the 1950s. The Weddell Gyre is very productive, because upwelling there lifts cold, nutrient-rich water.

  The Southern Ocean Observing System coordinates observation of the region. It provides access to metadata for much of the data gathered over past decades, with an emphasis on Essential Ocean Variables for the ocean south of 40 degrees south.

  At the Antarctic Convergence, cold Antarctic waters flowing north meet the warmer waters of the subantarctic, and the Antarctic water mostly sinks beneath. Mixing and upwelling there create a zone very high in nutrients. They feed phytoplankton, copepods and krill, and a food chain reaching to fish, whales, seals, penguins and albatrosses. Many consider this convergence the best natural definition of the ocean's northern extent.

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• 6. Krill and Its Eaters

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  Antarctic krill, Euphausia superba, has a biomass of around 500 million tonnes, which makes it one of the most abundant animal species on Earth. Each animal is about 6 centimetres long and weighs over a gram. Swarms can stretch for kilometres, packing up to 30,000 individuals into a cubic metre and turning the water red. They stay in deep water by day and rise at night to feed on plankton. In winter, when food is scarce, adults can revert to a smaller juvenile stage and live off their own bodies. Five krill species have been found in the Southern Ocean.

  Krill is the keystone species of the ecosystem. Whales, seals, leopard seals, fur seals, squid, icefish, penguins, albatrosses and many other birds all depend on it for food.

  Seven pinniped species inhabit Antarctica. The elephant seal, the largest, can reach 4000 kilograms, while females of the smallest, the Antarctic fur seal, reach only 150 kilograms. These two live north of the sea ice and breed in harems on beaches. Four other species can live on the ice. Crabeater and Weddell seals form breeding colonies, while leopard and Ross seals live solitary lives. All of them hunt underwater but breed on land or ice, where they have no terrestrial predators.

  Crabeater seals number around 15 million, which makes them one of the most numerous large animals on the planet. The four sea-ice species are thought to make up half of the world's seal biomass. The Weddell seal lives farther south than any other permanent mammal resident, and it is named after Sir James Weddell, who commanded British sealing expeditions in the Weddell Sea. The Antarctic fur seal was hunted very heavily in the 18th and 19th centuries for its pelt by sealers from the United States and the United Kingdom.

  Ten cetacean species live in these waters, six baleen whales and four toothed whales. The largest is the blue whale, which grows to 24 metres and weighs 84 tonnes. Many of them are migratory and travel to tropical waters during the Antarctic winter.

  Of the world's 18 penguin species, four live and breed on the Antarctic mainland and its close offshore islands, and another four live on the subantarctic islands. The emperor penguin is the only Antarctic animal to breed through the winter, kept warm by four overlapping layers of feathers. The Adélie penguin breeds farther south than any other penguin. The rockhopper has distinctive feathers around the eyes that look like elaborate eyelashes. King, chinstrap and gentoo penguins breed here too.

  Over 100 million birds nest on the rocky shores of mainland Antarctica and its offshore islands every spring. They include albatrosses, petrels, skuas, gulls and terns. The insectivorous South Georgia pipit is endemic to South Georgia and some smaller surrounding islands. Freshwater ducks live on South Georgia and the Kerguelen Islands.

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• 7. Clear Blood and Giants

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  More than 320 fish species have been described in the Southern Ocean, and tens more are still undescribed, especially among the snailfish. The snailfish family is the most species-rich, followed by the cod icefish and the eelpouts. Together with the other notothenioids, these account for almost nine in ten of the described species. Snailfish are generally found in deep water, while icefish also occur in shallower water.

  The crocodile icefish, family Channichthyidae, are found only in the Southern Ocean. They lack hemoglobin, so their blood is colourless, which earns them the name white-blooded fish. One of them, the mackerel icefish, was once the most common fish in coastal waters shallower than 400 metres. It was overfished in the 1970s and 1980s. Schools spend the day on the seafloor and rise at night to eat plankton and smaller fish. Many notothenioids carry antifreeze proteins in their blood and tissue, which let them live in water at or slightly below 0 degrees Celsius. Some snailfish have them too.

  Two species of toothfish, the Antarctic toothfish and the Patagonian toothfish, live on the seafloor between 100 and 3000 metres deep. They grow to around 2 metres, weigh up to 100 kilograms, and live up to 45 years. The Antarctic toothfish stays close to the mainland, while the Patagonian toothfish prefers the relatively warmer subantarctic waters. Both are fished commercially, and overfishing has reduced their numbers. The Antarctic silverfish is the only truly pelagic fish in the waters near Antarctica.

  On the seafloor, up to 155,000 animals have been found in a single square metre. The seabed environment is very similar all around Antarctica, so hundreds of species range right around the mainland. That is an unusually wide distribution for such a large community. Deep-sea gigantism is common. The isopod Glyptonotus antarcticus reaches 20 centimetres and 70 grams. More than 600 amphipod species are recognized south of the Antarctic Convergence, including giants such as the epimeriids, which reach 8 centimetres. Slow-moving sea spiders sometimes grow as large as a human hand, feeding on corals, sponges and bryozoans.

  The ocean holds around 70 cephalopod species. The largest is the colossal squid, Mesonychoteuthis hamiltoni, at up to 14 metres, one of the largest invertebrates in the world. Squid make up most of the diet of grey-headed albatrosses and sperm whales. Antarctic sponges are long-lived and sensitive to environmental change, because of the symbiotic microbial communities inside them. They therefore serve as indicators of environmental health.

  A census of sea life carried out during the International Polar Year, involving some 500 researchers, was released in 2010. It was part of the global Census of Marine Life. More than 235 marine organisms were found in both polar regions, across a gap of 12000 kilometres. Some large cetaceans and birds make the round trip every year. More surprising were small creatures such as mudworms, sea cucumbers and free-swimming snails. Deep-ocean temperatures at the poles and the equator differ by no more than 5 degrees, and major currents carry eggs and larvae. Closer study of such populations has often, but not always, shown closely related cryptic species rather than a single bipolar species.

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• 8. Rules and Resources

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  The International Whaling Commission's Southern Ocean Whale Sanctuary bans commercial whaling south of 40 degrees south. Between 50 and 130 degrees west, the ban reaches south of 60 degrees south. Japan regularly does not recognize the provision, and a Japanese fleet carried out an annual hunt under research permits. On the 31st of March 2014, the International Court of Justice ruled that Japan's program, long described as scientific, was a cloak for commercial whaling. No further permits would be granted.

  The Convention for the Conservation of Antarctic Seals was signed in London on the 11th of February 1972. The Convention for the Conservation of Antarctic Marine Living Resources entered into force on the 7th of April 1982. It arose largely from worry that rising krill catches could seriously affect the other marine life that depends on krill. Its area covers everything south of 60 degrees south, plus waters farther north up to the limit of the Antarctic Convergence. Many nations also prohibit mineral exploration and exploitation south of that convergence. The Antarctic Treaty covers the portion of the globe south of 60 degrees south and prohibits new claims to Antarctica.

  The ocean probably contains large, possibly giant, oil and gas fields on its continental margin. Placer deposits, accumulations of valuable minerals such as gold formed by gravity separation, are also expected. So are manganese nodules, rock concretions built in concentric layers of iron and manganese hydroxides around a core. Interest in such nodules stirred a great deal of activity among prospective mining consortia in the 1960s and 1970s. Meanwhile, the icebergs that form each year hold enough fresh water to meet the needs of every person on Earth for several months. For decades there have been proposals to tow them to arid places such as Australia. None has proved feasible or successful.

  Between the 1st of July 1998 and the 30th of June 1999, fisheries landed 119,898 tonnes, of which 85 percent was krill and 14 percent was Patagonian toothfish. In that same season, illegal, unreported and unregulated fishing landed an estimated five to six times more toothfish than the regulated fishery. International agreements to curb it came into force in late 1999. Long-line fishing for toothfish also kills many seabirds. The Antarctic ozone hole has raised ultraviolet radiation enough to cut phytoplankton productivity by as much as 15 percent. It has also started damaging the DNA of some fish.

  Few ports exist on the Antarctic coast, because ice limits use of most shores to short periods in midsummer. Even then, some need an icebreaker escort. Rothera Station, Palmer Station, Villa Las Estrellas, Esperanza Base, Mawson Station and McMurdo Station are among the major operational ports. Government research stations run most of them, and except in an emergency they stay closed to commercial and private vessels. Vessels in any port south of 60 degrees south are subject to inspection by Antarctic Treaty observers. The southernmost port is McMurdo Station, where Winter Quarters Bay forms a small harbour at the southern tip of Ross Island. A floating ice pier makes port operations possible there in summer. Operation Deep Freeze personnel built the first ice pier at McMurdo in 1973.

  Several yacht races describe their routes as passing through the Southern Ocean. In fact the courses run through the South Atlantic, South Pacific and Indian oceans, and never enter the ocean's actual geographical boundaries.

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