Slide 9: Proxy data sources: Ice cores
Data from ice cores is extracted in a number of ways.
Oxygen isotopic analysis (carried out with a mass spectrograph) gives an idea of the temperature at which the ice was deposited (since O18 has a higher vapour pressure, it is preferentially deposited). Thus, as water vapour travels to the poles, O18H2 will be deposited as water ice, and the polar fraction has a lower percentage of O18. In warmer conditions, more O18 will be found in the polar ice (Craig, 1961 ; Morgan, 1982).
Atmospheric gas concentrations can be extracted from bubbles formed by the closing off of air pores as firn turns to ice. (Raynaud & Lorius, 1973).
Physical variations in ice structure such as crystal size, incidence of melts and number/structure of bubbles give an idea of temperature and frequency of melt periods or deposition (Langway, 1970; Koerner, 1977)
Craig, H., 1961. Standard for reporting concentrations of deuterium and oxygen-18 in natural waters. Science, 133, pp. 1833-1834.
Koerner, R.M., 1977. Distribution of microparticles in a 299m core through the Devon Island ice cap, North West Territories, Canada. In: Symposium on Isotopes and Impurities in Snow and Ice, International Association of Scientifc Hydrology Publication No. 118. IASH, Washington D.C., pp. 371-376.
Langway, C.C., Jr., 1970. Stratigraphic analysis of a deep ice core from Greenland, Geological Society of America Special Paper 125. Geological Society of America, Boulder, Colorado.
Morgan, V.I., 1982. Antarctic Ice Sheet surface oxygen isotope values. J. Glaciol., 28, pp. 315-323.
Raynaud, D. & Lorius, C., 1973. Climatic implications of total gas content in ice at Camp Century. Nature, 243, pp. 283-284.