Both of these isotopes are produced by cosmic rays and solar irradiation impinging on the upper atmosphere, and both are quickly washed from the atmosphere by precipitation.
Of the irradiation dependent markers the two most important are 10Be and 36Cl.
Comparison with measurements made at South Pole station show that the ice core acts as a faithful recorder of atmospheric concentrations (see Fig.The 2000-year record from Law Dome, Antarctica, has been merged with modern records and a spline function was fit to the result to provide a 2000-year time series extending to the present These records are maintained by the World Data Center for Paleoclimatology, National Oceanic and Atmospheric Administration (NOAA), and have graciously been made freely available for access and distribution.The original investigators made the effort to obtain the data and assure their quality. Both 10Be and 36Cl are formed as charged ions in the ionosphere. Thus each annual layer starts 10Be and 36Cl poor, becomes 10Be and 36Cl rich, and then becomes poor again. Although what is said above is true, this is an exceedingly minor effect.Most ice core records come from Antarctica and Greenland, and the longest ice cores extend to 3km in depth.The oldest continuous ice core records to date extend 123,000 years in Greenland and 800,000 years in Antarctica. The major disadvantage of this dating method is that isotopes tend to diffuse as time proceeds. For similar reasons the ratio of deuterium to hydrogen acts the same way. 9Be and 35Cl) one can determine the season of the year the precipitation occurred. By comparing the ratios of these isotopes to their nonradioactive counterparts (i.e.