Stable Isotope Records from Greenland Deep Ice Cores: The Climate Signal and the Role of Diffusion.

NATO ASI Series, Vol 1 56. Ice Physics and the Natural Environment. Edited by John S. Wettlaufer, J. Gregory Dash and Norbert Untersteiner. Springer-Verlag, Berlin Heidelberg 1999

S.J. Johnsen
Science Institute, University of Iceland, Reykjavik .
H.B. Clausen
Departement of Geophysics, The Niels Bohr Institute of Astronomy, Physics and Geophysics, University of Copenhagen..
J. Schwander
Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland.
J. Jouzel
Laboratoire de Glaciologie et de Geophysique de l'Environnement, Centre National de la Recherche Scientifique St. Martin d'Héres, France.
and Laboratoire de Modélisation du Climat et de l'Environnement , Gif-Sur-Yvette, France.
A.E. Sveinbjörnsdottir
Science Institute, University of Iceland, Reykjavik, Iceland.
J. White
Institute of Alpine and Arctic Research and Department of Geological Sciences, University of Colorado, Boulder.

Glaciers and ice caps exert a strong influence on Earth's environment and climate. They can grow and decay, change the sea level, control the albedo and shape the mountains and continents on which they reside. During the last glacial period the espanding glaciers surged frequently and brought an enormous number of icebergs into the North Atlantic which caused a whole suite of violent climatic oscillations (Heinrich events, Dansgaard-Oeschger cycles)(Bond et al., 1992; Broecker et al., 1985; Johnsen et al., 1972)

The most peculiar peoiperty of glaciers is perhaps in the ability to perserve, throughout their "third dimension", a record of past climatic and environmental changes. Each annual layer of snow deposited on the surface of a cold ice cap carries with it, as it sinks slowly towards to the bottom, a fingerprint of the impurities present in the atmosphere. Even the atmospheric gases are carried along, trapped in small bubbles when the snow is transfomed into glacier ice.

The isotopic ratios O18/O16 or D/H (espressen in the following as the per mil deviations δ18O or δD relative to that of Standard Mean Ocean Water, SMOW) of te snow reflect the temperature at which the cloud vapour was transformed into ice crystals or snow, which provides us with an extremely important proxy for past temperature changes.

The annual layers are nicely stacked in the ice cap until they arrive near the botom strata where foldings and other stratigraphic disturbances form uneven bedrock undulations can disrupt the ordered layering. In Central Greenland this can happen after 150 thausand years or more and in smaller ice caps after 10 to 120 thausand years. By coring down to bedrock we can thus recover similarly old continuous records of the Earth's environment and climate.