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The Climate System and Climate Variations 1 3 Ice Cores and Palaeoclimate

Summary: The Climate System and Climate Variations 1
3 Ice Cores and Palaeoclimate
Katrine Krogh Andersen, Peter Ditlevsen and Jørgen Peder Steffensen,
Department of Geophysics, NBIfAFG, University of Copenhagen
1. Introduction
Ice sheets and glaciers form in areas where the annual snowfall exceeds the annual
melt-off over a long period of time. Today glaciers are found worldwide; but large ice
sheets are only found in the polar regions. Both glaciers and ice sheets build up from
snowfall and may thus be regarded as atmospheric sediment. This sediment contains
mainly the snow itself, but also samples of the past atmosphere are trapped in bubbles
in the ice. Along with the snow a wide range of different substances from the atmo-
spheric aerosol are deposited in the glacier.
As layer upon layer of consecutive snow falls are deposited in the glaciers accumula-
tion area the snow is buried and gradually transformed into ice due to the increasing
weight of the overburden snow. The ice layers are then further compressed by depth,
and they get thinner as they start to spread due to increasing pressure. This is visual-
ised in Figure 1. The glacier ice flows from the accumulation area down into the abla-
tion area where it is eventually lost as melt off or calving icebergs, i. e. ablation. If the
total accumulation of a glacier or an ice sheet is the same as the total loss, the glacier is
said to be in mass balance. The two largest ice sheets in the world, the Antarctic and


Source: Andersen, Katrine Krogh - Niels Bohr Institute for Astronomy, Physics and Geophysics, Københavns Universitets


Collections: Geosciences; Environmental Sciences and Ecology