Climatic Oscillations 1200–2000 AD

Abstract

THE idea of using the isotopic composition of glacier ice as a climatic indicator was proposed in 1954¹. The method is based on the fact that the concentration of heavy stable isotopes (deuterium and oxygen-18) in high polar snow increases with the temperature of formation of the snow^1–3. This causes seasonal variations in the isotopic composition of accumulated snow and ice⁴, as well as long-term variations due to climatic changes⁵. A unique possibility for studying palaeoclimates was offered when the US Army Cold Region Research and Engineering Laboratory succeeded in recovering a 1,400 metre long surface-to-bottom ice core from Camp Century on the North Greenland ice sheet⁶. No physical dating method can be applied on the relatively small amounts of ice available, so the age of the various increments of the core had to be calculated by considering a simple ice flow model⁸. This procedure turned out to be successful, in so far as the climate record that resulted from plotting the δ(¹⁸O) data (δ is defined⁷ as the relative deviation of the ¹⁸O/¹⁶O ratio of a sample from that of standard mean ocean water) against the calculated ages depicted known climatic events dated by other methods^5,9. In addition, unlike other methods, the stable isotope technique applied on the deep ice core gave an unbroken and detailed climatic record spanning probably 100,000 years.