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Antarctica is one of eight ecozones or biogeographical regions on Earth. With a surface area of 14 million km², to which are added 1.5 million km² of barriers, it is the fourth largest continent in the world. By convention, the geographical boundary is delimited by the so-called Antarctic convergence, the latitude where subtropical surface waters sink.
The area between 50° and the Antarctic polar circle is defined as subantarctic. The two largest ice shelves in the world, Ross and Filchner-Ronne, are located in Antarctica. The continent is surrounded by a large frozen area, the pack ice, in which one of the most interesting ecosystems on the planet develops and which represents the source of food for cetaceans, penguins, fish, seals and many birds.
There are over 70 lakes in Antarctica, located thousands of meters below the frozen blanket. The largest of these sub-glacial lakes is Lake Vostok, discovered by the Russian geographer Andrey Kapitsa during a series of Soviet scientific expeditions which took place between 1959 and 1964 near the Russian Vostok station.
The lake is believed to have been sealed by ice between 500,000 and one million years ago. There is evidence from core samples taken about 400 m above the lake's water surface that its waters may contain life forms (microbes).
Antarctica, due to its apparent uniformity, would seem to stand out from other continents, characterized by a variety of climates, ecosystems, peoples and cultures. In reality, the uniformity of Antarctica is only apparent, the effect of the great environmental and climatic diversity compared to other continents; in reality, even in this part of the world various types of climate, morphology and natural environments can be distinguished, significantly different from each other, but which appear similar because they are all characterized by a remarkably cold climate.
On average it is the coldest place on Earth and with the largest reserves of fresh water on the planet. The territory has the highest average altitude above sea level of all the continents. Antarctica is considered a desert, with annual rainfall of only 200 mm along the coast, and much less in inland regions.
The continent is crossed by the 3500 km long Transantarctic Range which extends from Cape Adare to Coats Land. The highest elevation occurs at the Vinsone Massif which is part of the Ellsworth Mountains in the Antarctic peninsula while the highest depression is the Bentley Subglacial Trench at 2538 m below sea level, located in the eastern part of the continent.
There are also some volcanoes on the continent, the highest of which is Mount Sidley. The ice sheet covering Antarctica is divided into the Eastern Ice Sheet and the Western Ice Sheet by the Transantarctic Range. The maximum thicknesses of the ice cap are found near Adélie Land, just 400 km from the coast: here there is a deep depression filled by 4776 m of ice.
If we consider the mass of ice that covers the surface, Antarctica is the continent highest on average above sea level. However, excluding the profile given by the ice caps and considering exclusively the average level of the rocky layer, this continent is on average the lowest.
With an average total volume of 26.6×106 km³, it constitutes 92% of the world's fresh water reserves. It has been calculated that the complete melting of Antarctica's ice would lead to a rise in ocean levels of around 70 metres.
