Antarctica is a desert because so little falls from its sky: the continent receives the equivalent of only about 150 mm of water a year on average, almost all of it as snow, and its interior gets less than 50 mm, which makes this 14.2 million km² continent the largest cold desert on Earth. About 98 percent of it is buried under an ice sheet averaging 1.9 km thick that holds roughly 70 percent of the world's fresh water; the other 2 percent is bare rock, of which the largest single piece is the McMurdo Dry Valleys, about 4,500 km² in Victoria Land. It is also the coldest place on the planet: Russia's Vostok Station recorded −89.2 °C on 21 July 1983. Life in this desert is concentrated at its edges. Penguins, seals and seabirds breed on the coastal sea ice and rocks and feed in the Southern Ocean, while the interior and the dry valleys hold only mites, midges, nematodes, mosses and lichens. Governed under the 1959 Antarctic Treaty, the continent has been designated by the Madrid Protocol, in force since 1998, as a "natural reserve devoted to peace and science". The sections below follow those species from the sea ice inland.
Emperor Penguins from Halley Bay to Cape Washington: 66 Colonies on Winter Ice
The animal most closely tied to the frozen desert is the emperor penguin, the tallest and heaviest penguin, weighing 22 to 45 kg. No other penguin raises its young through the Antarctic winter, and the emperor does so not on land but on stable sea ice near the coast, up to 18 km offshore, almost entirely between 66° and 77° south. In March and April adults walk 50 to 120 km from the edge of the pack ice to their colonies, choosing spots where ice cliffs and icebergs break the wind.
The cycle that follows is brutal. After the female lays a single egg she passes it to the male and returns to the sea for about two months. He balances the egg on his feet for 65 to 75 days in darkness and winds of up to 200 km/h, huddling with hundreds of other males that take turns in the warm centre. By the time the chick hatches he has fasted for around 120 days and may have lost as much as 20 kg. The female returns between mid-July and early August and finds him by his call.
Counting them is done from space. In 2009 the population was estimated at about 595,000 adults in 46 known colonies; the British Antarctic Survey then searched satellite images for guano stains on the ice, raising the number of known sites from 50 to 61 and the estimate to around 278,000 breeding pairs. By 2022, 66 breeding colonies were known. Major colonies include Cape Washington and Coulman Island in Victoria Land, Cape Colbeck and Halley Bay.
Because they depend on sea ice, emperors are sensitive to changes in it. Beginning in September 2015, a strong El Niño, high winds and record low sea ice caused almost total breeding failure at Halley Bay, the second-largest colony in the world, for three years running. Some breeders moved to the Dawson-Lambton colony 55 km to the south, which grew tenfold between 2016 and 2018. The IUCN moved the species from least concern to near threatened in 2012.
Adélie Penguins and Snow Petrels: Cape Adare, Cape Royds and the Inland Mountains
Where the emperor needs ice, the Adélie penguin needs the opposite: bare, rocky ground, ideally where wind or sun keeps the snow off. It is one of only four penguin species that nest on the continent itself, and its colonies are built of piled stones. Adults arrive in late October or November, when the colonies may still be up to 100 km from open water, and leave with their chicks in March. Ross Sea birds then migrate an average of about 13,000 km a year, following the edge of the sea ice to stay in daylight through winter.
A census in 2014, combining high-resolution satellite images with field surveys, counted about 3.79 million breeding pairs in 251 colonies, 53 percent more than a census 20 years earlier. The picture differs sharply by region. Colonies on the Antarctic Peninsula have declined since the early 1980s, by as much as 65 percent over 25 years as sea ice has shrunk, while those in East Antarctica have grown by more than enough to offset the loss. Some single colonies exceed a quarter of a million pairs: Cape Adare, in the Ross Sea region, averaged 227,000 breeding pairs across four seasons sampled between 1981 and 2012, and the Danger Islands off the Peninsula held 751,527 pairs in at least five colonies.
One bird pushes much deeper into the desert. The snow petrel, a small, pure white petrel, has the most southerly breeding sites of any bird. Most colonies are on exposed rock near the sea, but some lie in inland mountain ranges more than 400 km from open water, where the birds nest in deep rock crevices and lay a single egg between late November and mid-December. Far from the sea, they bathe in snow. It is one of only three birds ever seen at the geographic South Pole, along with the Antarctic petrel and the south polar skua, and with about 4 million adults it is classed as least concern. Altogether about 40 bird species breed on or close to Antarctica.
Weddell Seals Under the McMurdo Sound Fast Ice, and the Krill Beneath Them
Antarctica's seals live at sea and on its ice, and the one that stays closest to the continent is the Weddell seal. It spends its life on fast ice, the sea ice fixed to the shore, often right beside Antarctic research bases. In winter it stays in the water to avoid blizzards, keeping breathing holes open in the ice and poking only its head through them. It can dive to about 600 m and stay down for up to an hour. Pups are born on the ice between early September and November, weighing 25 to 30 kg, and double their weight in the first week.
Weddell seals are hard to count because they live across a vast ring of ice, but high-resolution satellite images from November 2011, when males are mostly underwater defending territories, gave an estimate of about 202,000 females. Their songs, repeated sequences of trills and calls, can be heard through the ice.
All of this coastal life rests on the ocean, not the land. Antarctic krill, a crustacean about 6 cm long, is the keystone species: its total biomass is around 500 million tonnes, making it one of the most abundant animals on the planet. Crabeater seals, the most numerous seal in the world, feed almost entirely on it, eating over 63 million tonnes a year. Seals, whales, birds, squid and fish together consume an estimated 152 to 313 million tonnes annually. Young krill shelter from predators in the cave-like underside of the pack ice, which is why sea-ice loss worries biologists, and its fishing has been regulated since the Convention for the Conservation of Antarctic Marine Living Resources came into force in 1980.
Midges, Mosses and Nematodes: Life on the Ice-Free Two Percent
On land, Antarctica's largest permanent resident is a 2 to 6 mm flightless midge, Belgica antarctica. It is the largest purely terrestrial animal native to the continent and the only insect that survives there year-round. Romanian biologist Emil Racoviță collected the first specimens during the Belgian Antarctic Expedition of 1897 to 1899, and the species is named after the place where it was collected, the channel the expedition called the "canal de la Belgica", now the Gerlache Strait, off the Antarctic Peninsula. It spends most of its two-year life as a larva, feeding on algae, fungi and decaying plant matter, can survive freezing down to about −15 °C and the loss of up to 70 percent of its body water, yet its larvae die within a week at just 10 °C.
Plants are just as limited. The flora consists mainly of about 100 species of mosses and 25 of liverworts, plus lichens. Only two native flowering plants grow in Antarctica, both on the Peninsula: Antarctic hair grass and Antarctic pearlwort, a yellow-flowered cushion about 5 cm tall. A hair grass specimen found on the Refuge Islands at 68°21′S in 1981 is listed by Guinness World Records as the southernmost flowering plant. A third flowering plant, annual bluegrass, is an introduced species. About 1,150 species of fungi have also been recorded in the Antarctic region.
The driest extreme is the McMurdo Dry Valleys. Here katabatic winds, cold dense air pulled downhill by gravity, evaporate fallen snow within hours in summer, the Transantarctic Mountains cast a snow shadow, and precipitation averages around 100 mm a year. Air temperatures have ranged from 12.0 °C at Taylor Glacier to −65.7 °C at Lake Vida. Even so, the valleys hold more than 6,000 lakes and ponds, fed by summer meltwater, and the Onyx River, Antarctica's longest river, flows here for a few weeks each summer. Life persists at microscopic scale: photosynthetic bacteria live inside rocks, and the nematode Scottnema lindsayae, half a millimetre to a millimetre long and endemic to Antarctica, eats microbes in the soil. It is sensitive to warming, and by 2006 its population had fallen 65 percent from 1993.
That makes the frozen desert a sensitive gauge of change, from penguin colonies on the coast to worms in the valley soils. The places behind these species have guides of their own: the Antarctic Dry Valleys, Antarctica's penguin colonies and the Antarctic ice sheet.