Greenland ice sheet

82 % of the area of Greenland is covered by the Greenland ice sheet

The Greenland ice sheet (also Greenland ice cap ) is an ice sheet, which covered an area of ​​about 1.8 million square kilometers, about 82 % of the surface of Greenland. It is the world's second largest permanently frozen surface after the Antarctic ice sheet.

Spatial extent

In a north-south direction, the length of the ice sheet is about 2,500 kilometers. The widest point of about 1,100 kilometers, is approximately 77 ° N to 78 ° N. In the middle, the ice is more than 1.5 km thick; in places, is the cardinality of more than three kilometers. The volume is estimated to be approximately 2.9 million cubic kilometers. Assuming a mean ice density of 917 kg / m³ results in a mass of about 2.67 million gigatonnes (2.67 · 1018 kg ). Would this ice completely melt, this would have a sea level rise of about seven meters result.

In most places the ice sheet reaches the sea not so have, unlike in Antarctica, formed no extensive ice shelves. Due to some great valleys, the ice -powerful outlet glaciers flows and reaches the sea, where they calve and produce most of the icebergs in the North Atlantic in this way. A well-known outlet glaciers on the west side of Greenland, the Jakobshavn Isbræ, which has at its end an exceptionally high flow rate of 20 to 22 meters per day and is responsible for about 10 % of all Greenland icebergs origin.

In addition to the ice sheet exist at the outer edge of Greenland glaciers and ice caps are still some isolated that cover a total of less than 100,000 square kilometers.

Formation

The ice of the existing ice sheet is at least 110,000 years old. However, there are indications that the ice sheet in the early Pleistocene or late Pliocene from coalescing ice caps and glaciers originated - but not much earlier. At this time, the continental glaciation of the northern hemisphere began in the context of the currently ongoing Quaternary Ice Age.

Cause of glaciation of Greenland lies possibly in the collision of the South American with the Caribbean plate and the resulting final closure of the Isthmus of Panama 2.4 million years ago. By separating the Pacific and Atlantic Oceans, the global oceanic flow system changed. The Gulf Stream transported from then on warm surface water far into the North Atlantic. The increased evaporation and thus cloud formation rate over the North Atlantic led to more snow on the northern hemisphere - an important factor for the glaciations during the Quaternary Ice Age and the formation of the Greenland ice sheet.

Because of the weight of the ice the earth's crust beneath sinks into the mantle (see → isostasy ). Therefore, the largest part of the buried ice from the land surface of Greenland is located at sea level or even lower.

Climate

On the ice sheet temperatures are lower than in the other regions of Greenland. It will reach annual lows of below -30 ° C. In summer the top layer of ice thaws on, which leads through the formation of air bubbles in the ice, that this appears completely white. In winter, the ice on the other hand takes a clear, blue-green tint.

The ice sheet as documentation of climate change

The ice sheet consists of compressed snow that has accumulated over a period of more than 100,000 years. For up to three kilometers deep holes were sampled from which to draw conclusions about the temperatures in the past, the expansion of the oceans, precipitation, chemical composition of the atmosphere, volcanic activity and many other events and situations can be drawn recent Earth history.

Influence of global warming

The ice sheet is melting in recent years from a record pace. Between 1979 and 2002, the area in the summer months affected by the melting has increased by 16%. The drainage of melt water through gaps and cracks in the ice which in turn acts back on accelerating the thawing process. In a study conducted by the Jet Propulsion Laboratory of NASA is believed that this is also reason for that move the glaciers of Greenland, with increasing speed towards the sea. According to satellite measurements grew between 1996 and 2005, the annual ice loss of 96 km3 to 220 km3, and in the years 2006 to 2008 to an average of 273 km3 per year. Other measurements that adding the individual losses of all glaciers result, for the year 2008 a net loss of 145 km3.

Published in 2001 3 Report of the Intergovernmental Panel on Climate Change predicts a sea level rise of 0.2 to 0.6 meters with a global mean warming of three degrees Celsius 1990-2090. About two-thirds of this increase is based on the thermal expansion of sea water, while one-third is due to the melting of land ice. Partial melting of the ice sheets Gröndlands and Antarctica was not been considered because of insufficient facts. An average loss of the Greenland ice sheet annually 100 km3 would lead to a sea level rise of 0.03 meters over 100 years.

A global warming of more than 3 degrees Celsius would heat the ice sheet over a threshold. The complete melting of the Greenland ice sheet leading to a sea level rise of 7.2 m. Since Greenland mainland soil is almost completely near or below sea level, it is possible that the country is by melting of the ice sheet first under the sea and the coastal mountains of Greenland to island groups would. A subsequent general elevation of the Greenland continental shelf would be possible, however, because today's powerful ice load were not true.

Another hypothesis states that with regard to increased melting of the ice sheet due to increased freshwater input into the Atlantic Ocean from a certain threshold the thermohaline circulation of the North Atlantic drift could be as far as disturbed as driving the Gulf Stream system, the hot water flow of the Gulf Stream would be significantly reduced. Thus, the temperature rise could slow down in the North Atlantic to Europe, and the melting rate of the Greenland ice sheet stabilizing. A change in the flow conditions in the oceans is discussed as one of the reasons for the emergence of a cold period.

A study by the Technical University of Denmark demonstrates that even the north-east of Greenland ice sheet begins to melt. So far, this region was considered to be stable. This realization has resulted after evaluating the data of ice thickness measurements by aircraft and satellites for the years 2003 to 2012. According to the researchers, the region has lost tens of billions of tons of ice per year since 2003, it will allow the Northeast Greenland have contributed about 0.03 millimeter to sea level rise. Cause of the melt was probably a chain reaction on the warm summer in 2003.