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In this method one compares certain inclusions in a ice-core whose age has been determined with a seperate method to similar inclusions in an ice-core of a still undetermined age.
These inclusions are typically ash from volcanic eruptions and acidic layers.
Of the temperature dependent markers the most important is the ratio of 18O to 16O.
A major disadvantage of these types of dating is that they are extremely time consuming.
Of these are items that depend on the temperature (colder in the winter and warmer in the summer) and solar irradience (less irradience in winter and more in summer).
For similar reasons the ratio of deuterium to hydrogen acts the same way. 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.The amount of "leakage" depends on the height of the ionosophere, which changes primarily in response to the Solar cycle, with periods of maximum solar activity corresponding to the highest extent of the ionosphere.It should be noted that the 10Be/9Be ratios for some ice cores have been compared with the known solar cycle and are in excellent agreement with what is known (accurately showing the time of the European Little Ice Age, which corresponded with a remarkably low amount of solar activity).
The major disadvantage of this dating method is that these isotopes also tend to diffuse over time.