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The Greenland ice sheet ((グリーンランド語:Sermersuaq)) is a vast body of ice covering , roughly 80% of the surface of Greenland. It is the second largest ice body in the world, after the Antarctic Ice Sheet. The ice sheet is almost long in a north-south direction, and its greatest width is at a latitude of 77°N, near its northern margin. The mean altitude of the ice is .〔Encyclopaedia Britannica. 1999 Multimedia edition.〕 The thickness is generally more than and over at its thickest point. It is not the only ice mass of Greenland – isolated glaciers and small ice caps cover between around the periphery. If the entire of ice were to melt, it would lead to a global sea level rise of .〔Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) (J.T.,Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K. Maskell, and C.A. Johnson (eds.) ). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 881pp. (),(), and ().〕 The Greenland Ice Sheet is sometimes referred to under the term ''inland ice'', or its Danish equivalent, ''indlandsis''. It is also sometimes referred to as an ice cap. The ice in the current ice sheet is as old as 110,000 years.〔Meese, DA, AJ Gow, RB Alley, GA Zielinski, PM Grootes, M Ram, KC Taylor, PA Mayewski, JF Bolzan (1997) ''The Greenland Ice Sheet Project 2 depth-age scale: Methods and results.'' Journal of Geophysical Research. C. Oceans. 102(C12):26,411-26,423.〕 The presence of ice-rafted sediments in deep-sea cores recovered off of northeast Greenland, in the Fram Strait, and south of Greenland indicated the more or less continuous presence of either an ice sheet or ice sheets covering significant parts of Greenland for the last 18 million years. From just before 11 million years ago to a little after 10 million years ago, the Greenland Ice Sheet appears to have been greatly reduced in size. The Greenland Ice Sheet formed in the middle Miocene by coalescence of ice caps and glaciers. There was an intensification of glaciation during the Late Pliocene.〔Thiede, JC Jessen, P Knutz, A Kuijpers, N Mikkelsen, N Norgaard-Pedersen, and R Spielhagen (2011) ''Millions of Years of Greenland Ice Sheet History Recorded in Ocean Sediments.'' Polarforschung. 80(3):141-159.〕 The weight of the ice has depressed the central area of Greenland; the bedrock surface is near sea level over most of the interior of Greenland, but mountains occur around the periphery, confining the sheet along its margins. If the ice disappeared, Greenland would most probably appear as an archipelago, at least until isostasy lifted the land surface above sea level once again. The ice surface reaches its greatest altitude on two north-south elongated domes, or ridges. The southern dome reaches almost at latitudes 63°–65°N; the northern dome reaches about at about latitude 72°N. The crests of both domes are displaced east of the centre line of Greenland. The unconfined ice sheet does not reach the sea along a broad front anywhere in Greenland, so that no large ice shelves occur. The ice margin just reaches the sea, however, in a region of irregular topography in the area of Melville Bay southeast of Thule. Large outlet glaciers, which are restricted tongues of the ice sheet, move through bordering valleys around the periphery of Greenland to calve off into the ocean, producing the numerous icebergs that sometimes occur in North Atlantic shipping lanes. The best known of these outlet glaciers is Jakobshavn Glacier ((グリーンランド語:Sermeq Kujalleq)), which, at its terminus, flows at speeds of per day. On the ice sheet, temperatures are generally substantially lower than elsewhere in Greenland. The lowest mean annual temperatures, about , occur on the north-central part of the north dome, and temperatures at the crest of the south dome are about . During winter, the ice sheet takes on a clear blue/green color. During summer, the top layer of ice melts leaving pockets of air in the ice that makes it look white. == The ice sheet as a record of past climates == The ice sheet, consisting of layers of compressed snow from more than 100,000 years, contains in its ice today's most valuable record of past climates. In the past decades, scientists have drilled ice cores up to deep. Scientists have, using those ice cores, obtained information on (proxies for) temperature, ocean volume, precipitation, chemistry and gas composition of the lower atmosphere, volcanic eruptions, solar variability, sea-surface productivity, desert extent and forest fires. This variety of climatic proxies is greater than in any other natural recorder of climate, such as tree rings or sediment layers. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Greenland ice sheet」の詳細全文を読む スポンサード リンク
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