Antarctica

I

Introduction

Antarctica, fifth largest of the Earth’s seven continents. The southernmost, coldest, windiest, highest, most remote, and most recently discovered continent, it surrounds the South Pole, the point at the southern end of the Earth’s axis. Almost completely covered by ice, Antarctica has no permanent human population. The continent is ringed by the Southern Ocean. The entire area south of the Antarctic Convergence, which serves as the northern boundary of the Southern Ocean, is referred to as the Antarctic region. Antarctica means “opposite to the Arctic,” the Earth’s northernmost region.

The continent is shaped somewhat like a comma, with a round body surrounding the pole and a tail curving toward South America. The round portion, lying mainly in the Eastern Hemisphere, makes up East Antarctica. The tail and its thickened base, located entirely in the Western Hemisphere, form West Antarctica. Antarctica lies 1,000 km (600 mi) from South America, its nearest neighbor; 4,000 km (2,500 mi) from Africa; and 2,500 km (1,600 mi) from Australia. Antarctica’s latitude (location in relation to the equator) and high elevations make it the coldest continent. Air temperatures of the high inland regions fall below –80°C (-110°F) in winter and rise only to –30°C (–20°F) in summer. The warmest coastal regions reach the freezing point in summer but drop well below in winter.

The last continent to be discovered, Antarctica remained hidden behind barriers of fog, storm, and sea ice until it was first sighted in the early 19th century. Because of the extreme cold and the lack of native peoples, forests, land animals, and obvious natural resources, the continent remained largely neglected for decades after discovery. Scientific expeditions and seal hunters had explored only fragments of its coasts by the end of the 19th century, while the interior remained unknown. Explorers first reached the South Pole in 1911, and the first permanent settlements—scientific stations—were established in the early 1940s. From that time the pace of exploration accelerated rapidly. Scientists continue to conduct research in Antarctica, and in recent years increasing numbers of tourists have visited Antarctica to appreciate the region’s majestic scenery and wildlife.

Seven nations—Argentina, Australia, the United Kingdom, Chile, France, New Zealand, and Norway—claim territory in Antarctica. Other nations, including the United States and Russia, do not acknowledge these claims and make no claims of their own, but reserve rights to claim territory in the future. Since 1961 the continent has been administered under the Antarctic Treaty, an international agreement to preserve the continent for peaceful scientific study.

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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.

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