Greenland Cores

GREENLAND IS THE largest island in the world. Most of Greenland is covered with an enormous ice cap that is almost three times the size of Texas. The ice cap covers about 90 percent of the island. It is so heavy that its weight has depressed the center of Greenland to about 1,000 ft. (304 m.) below sea level. The Greenland icecap contains one-eighth of the total global ice-mass. Most of the remaining ice mass is in Antarctica. Some parts of northern Greenland are ice-free because it is too cold for snow to form. In some southern parts, [Page 474]the area is too warm for ice to accumulate. The ice cap has been created by the accumulated weight of snowfall through hundreds of thousands of years. The shrinkage in the ice cap, since it was first measured in the 1950s, is due to global warming.

Scientists who specialize in paleoclimate research have drilled two ice core samples in the center of the Greenland ice cap. The core samples were drilled to a depth of 2 mi. (3.2 km.). 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, regionally and globally, for the last 100 thousand years. Strictly speaking, the ice cores report what occurred climatically only 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 today. The age of the plants, as well as the insect life found, is between 500,000 and 1 million years in 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 perhaps did not exist perhaps as long as 2.5 million years ago. 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, the two elements in a water molecule. The air bubbles, the isotopes, and the organic material in the ice cores have given scientists materials that are enabling them to create a picture of the climate of the Earth over the last 1 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.

Concentrations of different gases in the air bubbles trapped in ice core samples record the levels of greenhouse gases in the atmosphere over a long stretch of geologic history. The concentrations of carbon dioxide, methane, and nitrous oxide reveal the greenhouse gas levels that are used to interpret the climatic changes over the last 1 million years. Some of the trace molecules in the samples were aerosols, which are indications of vast volcanic activity. Other inclusions in the ice core sample may be dust or volcanic ash, pollen, and radioactive elements. Ice core samples from Greenland can be compared with the results from ice core samples taken from Antarctica and from other major glaciers around the world. The conclusions of scientists have included inferences about solar variability, forest fires, and the water drawn from the sea through evaporation.

...