Ice sheet
As an ice sheet or ice cap is called an extended, firm land covering glaciers with an area of more than 50,000 km ² (smaller, similarly shaped glacier is called ice caps ). He buries the existing relief almost entirely to themselves. The movement of the ice is also only marginally affected by this.
Spread of ice sheets
Currently exist on Earth only the ice sheets of Greenland and Antarctica. During the ice ages, as the Last Glacial Maximum ( LGM ) about 21,000 years ago, as well as the Laurentide and Cordilleran ice sheet of the adjacent Barents - Kara ice sheet covered large parts of North America, the Fennoscandian ice sheet (also called Scandinavian ice sheet called ) Northern Europe, parts Northern Asia, and the Patagonian ice sheet to the south of South America. The existence of a glacial ice sheet Tibetan is controversial.
Although the surface of an ice sheet is cold, the Eisbasis is generally warmer and reaches in some places the pressure melting point. The melt-water generated can act as a lubricating film and accelerate the ice movement strong. This fast-flowing channels can form in the ice sheet, the so-called ice streams.
Today's ice sheets are geologically young. The Antarctic ice sheet is formed first from ice caps in the early Oligocene, the repeatedly stretched and pulled back, until finally almost the whole of Antarctica was ice-covered from the Pliocene. The Greenland ice sheet was formed only in the late Pliocene, associated with the first continental glaciation ( ice age ). Since this happened relatively quickly, were fossils of plants that grew there before, much better preserved than in the Antarctic ice sheet gradually incurred.
Antarctic ice sheet
The Antarctic ice sheet is the largest single mass of ice on earth. It covers an area of about 14 million square km and contains 30 million cubic kilometers of ice, which corresponds to about 90 percent of the total freshwater inventory of the earth's surface. Upon complete melting of a global sea level rise of about 61.1 meters would result. In the East Antarctic ice sheet rests on the a large land mass, whereas the subsoil of the West Antarctic ice sheet is up to 2500 m below sea level. Without the presence of the ice would be seabed here; it is therefore also called a marine ice sheet.
The Antarctic ice sheet is almost completely surrounded by ice shelves, fed by ice streams and Auslassgletschern of the ice sheet. The largest ice shelves are the Ross Ice Shelf, the Filchner - Ronne Ice Shelf Amery Ice Shelf and the.
New research has found here bacteria in an underground lake that do not require oxygen and light.
Greenland Ice Sheet
The Greenland ice sheet covers 1.7 million square kilometers about 82 percent of the land area of Greenland, has a volume of 2.85 million km ³ and would cause a global sea level rise of about 7.2 meters when fully melting
Possible effects of global warming
Because of global warming, an increase of ice volume during the 21st century is predicted for the Antarctic ice sheet. The reason for this is that the warming in the very cold Antarctic may cause any appreciable gain of ice melting, but the snowfall amount increases. The warmer Greenland ice sheet is likely to lose significant contrast by melting volume. It is possible that both effects compensate roughly. More recent data show that losses have the ice sheets of Greenland and Antarctica between 1993 and 2003 very likely contributed to sea level rise (pp. 5f. ). However, the uncertainties in the measurement of the masses of ice are considerable, and the dynamics of the ice is not yet fully understood.