How Ice Cores Record a History of Climate How can a history of climate be reconstructed from an ice core?
When snow falls it carries with it the compounds that are in the air at the time, compounds ranging from sulfate, nitrate and other ions, to dust, radioactive fallout, and trace metals. When snow falls in a place where temperatures above freezing are rare (there is only a hint of any melting at the GISP2 site in the 750 year record recovered to date), such as in polar regions or at high altitude, the snow from one year falls on top of the previous year without melting. As each years snowfall is buried by successive years’ snowfall, the constituents contained in the snow are buried along with it. By drilling down from the surface of an ice sheet and analyzing snow from greater and greater depths, a history of the compounds in the air can be obtained. Further, snow that is deeper than 80 meters at the GISP2 site turns into ice from the weight of the snow above it, and trapped in the ice are small bubbles of air. Thus, in addition to trapping compounds from the air, an ice sheet traps a s
