II.

Land and Climate

With an area of 14 million sq km (5.4 million sq mi), Antarctica is larger than either Europe or Australia. Its average elevation of more than 2,000 m (6,500 ft) is over twice that of Asia, the next highest continent. However, much of this mass is ice. Below this ice, East Antarctica is a landmass about the size of Australia, and West Antarctica is a collection of islands. Only 2.4 percent of the total continental area is exposed rock. Exposed areas include the peaks of several mountain ranges and other smaller scattered outcrops, both of which poke through the ice cover, as well as dry valleys, glacier-carved areas that are kept clear of snow by gusty winds. Only about 2 percent of the coast is exposed cliffs or beaches; the rest is made up of ice cliffs that extend beyond the end of the continental rock.

The Ross and Weddell seas indent the thickened base of West Antarctica where it meets East Antarctica, while the Amundsen and Bellingshausen seas lie at West Antarctica’s outer edge. Numerous bays also indent the outer edge of East Antarctica, creating a jagged coastline.

A.

Land of Ice

The total volume of the ice sheet covering Antarctica is estimated at 29 million cu km (7 million cu mi), or about 90 percent of the world’s ice. If the ice sheet melted, the oceans of the world would rise by 60 m (200 ft). Some 11 percent of the ice sheet consists of ice shelves—massive floating slabs of permanent ice fringing the continent—that are anchored to the rock and extend into the surrounding ocean. The largest, Ross Ice Shelf, is about the size of France. The Antarctic ice sheet has an average thickness of 2,160 m (7,090 ft); its greatest recorded depth is more than 4,700 m (15,400 ft).

Antarctica’s ice sheet formed over millions of years. As new snow falls, it compresses the layers of older snow beneath it into ice. The physical characteristics of the ice sheet are constantly changing as new ice forms and slides outward toward the coasts. Large masses of moving ice known as glaciers move down the continent’s five major drainage systems in two ways. If there is a layer of water between the glacier and the bedrock beneath it, the whole glacier can slide under the force of gravity. Alternatively, the weight of the accumulated snow and ice can cause the ice crystals of the glacier to form into layers, which glide over one another. Glaciers flow either into ice shelves or directly out to the edges of the continent, where portions break off and form floating masses called icebergs (see Ice: Icebergs). Carried by circumpolar currents and prevailing winds, these icebergs drift westward around the continent and then northward to the Antarctic Convergence before gradually breaking up and melting upon contact with warmer waters.

In addition to icebergs, ocean waters close to the continent contain floating sea ice, some attached to the land (fast ice) and some drifting with wind and currents (pack ice). Sea ice melts and freezes seasonally, covering up to 21 million sq km (8 million sq mi) in late winter and only 5 million sq km (2 million sq mi) in summer.

B.

Land Regions

During the Mesozoic Era (about 240 million to 65 million years ago) Antarctica was a central part of Gondwanaland, an ancient landmass that consisted of the present continents of South America, Africa, Antarctica, and Australia as well as the Indian subcontinent. Evidence from oceanic ridges surrounding Antarctica indicates that Gondwanaland began to break up about 150 million years ago. Antarctica gradually drifted towards the South Pole, arriving near its present polar position about 100 million years ago. Climatic cooling caused the gradual formation of the Antarctic ice sheet.

East Antarctica makes up about two-thirds of the continent’s area. The land beneath the ice consists of a basement complex of ancient gneisses, schists, and other metamorphic rocks overlaid by sediments from the Cambrian and Permian periods. Containing evidence of tropical forests and deserts prior to the more recent glacial conditions, these layers reflect the region’s complex climatic history. Covering the land is a huge, complex ice dome rising from coastal plains to a high plateau more than 4,000 m (13,000 ft) in elevation. The Transantarctic Mountains stretch 3,500 km (2,200 mi) along the entire western flank of East Antarctica, separating it from West Antarctica. This range holds back the plateau ice of East Antarctica like a massive dam, penetrated by glaciers that flow into the Ross and Filchner-Ronne ice shelves to the west. High peaks—some rising to more than 4,300 m (14,000 ft)—poke through the ice sheet, and other portions of the range are dry valleys that are free of ice. Toward the Indian and Pacific ocean coasts lie several minor ice domes and lower plateaus, some penetrated by other mountain ranges.

In East Antarctica, at the center of the continent, is the South Pole, also known as the south geographic pole. The South Pole is the point where all lines of longitude converge. Off the Adélie Coast of East Antarctica is the south magnetic pole, the location to which the south-seeking end of a compass needle points due to the Earth’s magnetic fields. Located on land when it was first reached in 1909, the south magnetic pole has migrated gradually out to sea with changes in the fields, a phenomenon known as polar wandering.

The remaining third of the continent, West Antarctica, consists of a much lower, undulating ice sheet covering a complex of mountainous islands. The Antarctic Peninsula, the “tail” of land reaching toward South America, was formed by the same geologic processes that formed the Andes Mountains on that continent. Many islands, including the South Shetland Islands, lie off the Antarctic Peninsula. Deep trenches and basins beneath the ice separate the islands of West Antarctica. Vinson Massif, the highest point in Antarctica, has an elevation of 4,897 m (16,066 ft) and lies in the Sentinel Range near the Filchner-Ronne Ice Shelf. Several active volcanoes, including Mount Erebus on Ross Island, dot coastal and island areas. The multilayered land formations of West Antarctica, folded and transformed by geologic structural deformations, reveal a distinct, more turbulent geological history than that of East Antarctica. These formations consist of a Precambrian basement covered by volcanic sediments from the Carboniferous Period, Mesozoic Era, and Tertiary Period. These volcanic sediments are in turn covered by plant-bearing Jurassic and later Tertiary sediments.

C.

Climate and Weather

Antarctica has several climates, all cold but differing considerably in severity. East Antarctica’s high plateau region yields the lowest year-round temperatures due to its relatively high elevation. The world’s lowest yearly air temperatures, typically –88°C (–126°F), are recorded in late August at Russia’s Vostok station. In coastal regions latitude is more significant than elevation. The higher the latitude—that is, the closer to the pole—the lower the average temperatures. The west coast of the Antarctic Peninsula and the neighboring islands have the mildest climates, with average January temperatures above freezing.

The entire region south of the Antarctic Circle, which is the parallel of latitude at 66°30’ south, experiences at least one day of continuous daylight during the Southern Hemisphere’s summer (around December 21) and one day of continuous darkness during the winter (around June 21). The interior of Antarctica has almost continuous daylight during the summer and darkness during the winter. In coastal areas farther north, there are fewer days of continuous daylight and darkness, and sunrises and sunsets occur more frequently.

Precipitation falls mainly as snow or ice, with occasional rain in coastal areas. Very little precipitation falls on the high plateau. Average annual accumulations of 50 mm (2 in) there make it one of the world’s driest deserts. Successive low-pressure systems around the coasts and islands bring heavier snow, which is packed down by wind and its own weight to form ice. Winds are light and variable on the plateaus, rarely reaching more than 30 km/h (20 mph), but are strong and persistent closer to the coasts. Katabatic, or downslope, winds blow cold, dense air down the steep slopes from the interior highlands onto the lower ice slopes.

D.

Optical Phenomena

Antarctica experiences many unique atmospheric optical phenomena. Most spectacular is the aurora australis (southern lights), caused by entry into the upper atmosphere of streams of charged particles (mainly protons and electrons) from the Sun. Deflected by the Earth’s magnetic field, the particles collide with atoms and molecules of atmospheric gases 100 to 140 km (60 to 90 mi) above the Earth’s surface. This produces light in characteristic rays, bands, and rings of various hues. Within the southern auroral zone—a wide circle about 4,000 km (about 2,000 mi) in diameter and centered around the geomagnetic pole (the south end of the axis of the geomagnetic field that surrounds the Earth)—auroral displays are visible almost every winter night, including the 24-hour-long polar night.

Refraction of light from the Sun and Moon by concentrations of ice crystals in the lower atmosphere produces iridescent clouds in the sky and rainbow-like halos around the Sun and Moon. Dry atmosphere chilled by contact with the cold surface of the Earth gives rise to spectacular mirages, in which distant objects are raised above the horizon to appear misleadingly close. Similar atmospheric distortions produce colored disks resembling the Sun and Moon—called parhelia, or sun dogs, and parselene respectively—as well as colored arches in the sky.

E.

Vegetation

Almost completely covered by thick ice, Antarctica has very little land available for soils to form or vegetation to settle. Existing soils were formed late in the continent’s geologic history and have little organic content or water-holding capacity. Isolation from other continents makes it difficult for new types of vegetation to spread to Antarctica. Constant low temperatures, high winds, and lack of moisture discourage all but the hardiest plants, which may be capable of active growth for only a few days per year. These factors limit plant life in Antarctica almost entirely to protists (simple, often one-celled organisms), algae, lichens, and mosses. Only two known species of flowering plants, both found only on the Antarctic Peninsula and neighboring islands, grow in Antarctica. The continent has no equivalent of Arctic tundra, which supports a greater variety of plant life: Antarctica’s richest vegetation compares with the northernmost, scarcest Arctic polar desert vegetation. Nevertheless, patches of vegetation grow on all known rocky outcrops in Antarctica, to within 290 km (180 mi) of the South Pole. Snow algae grow on snow and ice surfaces close to the coast, especially along the Antarctic Peninsula where seabird droppings and sea spray provide nutrients.

Antarctic waters support other types of vegetation. Coastal seaweeds thrive on and around islands near the Antarctic Convergence, but are inhibited farther south where sea ice scrapes the shores. The cold waters of the Southern Ocean support masses of phytoplankton—minute floating plants including diatoms, dinoflagellates, and other algae—that proliferate in summer, especially in areas where upwelling brings nutrient-rich waters to the surface (see Marine Life: Environmental Factors). Phytoplankton provides a rich source of food for marine animals.

F.

Animal Life

The harsh climate and sparse vegetation of Antarctica’s land regions support only microscopic animals and primitive insects. Protozoa, nematodes, tardigrades, and other minute forms inhabit damp soils. Other invertebrate species include springtails and mites. The wingless midge, which grows up to 12 mm (0.47 in) long, is the largest land animal.

In contrast to the land, the Southern Ocean supports a wide variety of animal life, which all depends directly or indirectly on the phytoplankton of the surface waters. Zooplankton—including krill, copepods, arrowworms, jellyfish, fish larvae, and larval forms of bottom-dwelling starfish, bristle worms, anemones, and mollusks—feed on phytoplankton. Zooplankton in turn provide food for fish and squid, both of which are abundant in Antarctic waters. Concentrated swarms of zooplankton (especially of krill and young fish), together with larger fish (especially of superfamily Notothenioidea) and squid, provide food for the seals, whales, and seabirds that are Antarctica’s major predators and most prominent animals. Seven species of whales and eight species of dolphins feed in the Southern Ocean; several penetrate far south into the pack ice during the summer. Seven species of seals breed within the Antarctic region, some on southern island shores and some exclusively within the pack ice region. About 40 species of seabirds—including 7 species of penguins, 4 species of albatross, 20 species of petrels, as well as cormorants, gulls, skuas, and terns—breed within the region, mainly on islands and continental coasts.

Large marine animals played an important role in attracting humans to Antarctica: Sealers and whalers contributed substantially to the early exploration of the Southern Ocean and coastal regions. Fur seals and southern elephant seals of the islands near the Antarctic Convergence were hunted for skins and oil throughout the 19th century until economically profitable stocks were depleted. Hunting of elephant seals continued into the 1950s. From 1904 through the 1960s whalers hunted large migratory whales (blue, fin, sei, humpback, and sperm whales) for oil in Antarctic waters from whaling stations on several Antarctic islands and from floating factory ships. Beginning in the 1960s concern that seals and whales would be hunted to extinction prompted several measures to protect surviving populations. See the Management and Conservation section of this article, below.

G.

Mineral Resources

Although only about 1 percent of the continent’s ice-free areas have been surveyed for minerals, evidence indicates that Antarctica contains rich mineral deposits. The Transantarctic Mountains contain huge deposits of coal as well as copper, lead, zinc, silver, tin, and gold. The Prince Charles Mountains of East Antarctica are rich in iron ore; the Antarctic Peninsula contains copper and molybdenum ores; and the Dufek Massif includes ores of chromium, platinum, copper, and nickel. It is also believed that deposits of petroleum and natural gas exist in the continental shelf regions, such as the area under the Ross Sea. Although Antarctica has prospects for mineral development, there are concerns about the potential environmental and political impacts of this development. In 1991 the signatory nations of the Antarctic Treaty agreed to a 50-year moratorium on commercial mining activity. The only mineral resources currently used are sand, gravel, and crushed rocks for constructing airstrips and building foundations at the scientific stations.