Greenland Ice Cores

Greenland is the largest island in the world. About 90 percent of Greenland is covered with an enormous ice cap that is almost three times the size of Texas. Created by the accumulated weight of snowfall through hundreds of thousands of years, the ice cap is so heavy that its weight has depressed the center of Greenland to about 1,000 ft. below sea level. The Greenland ice cap contains one-eighth of the total global ice mass, most of which is in Antarctica. A portion of the northern part of Greenland is ice-free because it is too cold to snow. In some southern areas, the area is too warm for ice to accumulate. The ice cap has partially shrunk since it was first measured in the 1950s, and the shrinkage has been attributed to global warming.

American scientists began drilling ice cores in Greenland in 1956 and 1957. In the 1960s, further drilling revealed a detailed record of the climate for the last 120,000 years. Scientists who specialize in paleoclimate research have drilled ice core samples at two locations within 18 mi. (30 km) of each other in the center of the Greenland ice cap. Two projects drilled to bedrock at a depth of 2 mi. (3.2 km): the European Greenland Ice Core Project (GRIP) drilled between 1989 and 1992, and the American Greenland Ice Sheet Project (GISP2) ended in 1993. The ice cores are in an area where winter snowfall has constantly added depth to the ice cap over thousands of years. The ice caps have been studied as an environmental record of the climate, both regional and global, for the last 100,000 years. Strictly speaking, the ice cores report only what occurred climatically where the samples were taken. However, extrapolations provide an estimate of global weather conditions and thus a record of the Earth’s climate through several ice ages.

Plant materials in the cores are some of the oldest plant material currently available on the Earth. The plant materials reveal that the climate of the Earth was much warmer hundreds of thousands of years ago than it is today. The age of the plants, as well as the insect life found, is estimated to be between 500,000 and 1 million years of age. 

In addition, remains of boreal forests were found. The implications of the plant and insect materials in the ice cores indicate that the ice cap did not exist perhaps as long ago as 2.5 million years. However, in more recent geological ages, the ice cap did not completely disappear during interglacial

periods. As the snow accumulations have compressed over the millennia, they have also been squeezed into ice, which has trapped air bubbles. The ice cores, composed mostly of water, also contain isotopes of oxygen and hydrogen that are the two elements in a water molecule. The air bubbles, isotopes, and organic material in the ice cores have enabled scientists to create a picture of the climate of the Earth over the last million or more years. The heavier isotopes have a lower vapor pressure, so they condense more rapidly as temperatures cool than is the case with normal water molecules. The concentration of isotopes is an indication of the temperature at the time of the precipitation of the water molecule under study.