Encyclopedia of scientific dating methods
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).
The basis of this method lies with looking for items that vary with the seasons in a consistent manner.
As the water vapor travels towards the poles it becomes increasingly poorer in H2(18O) since the heavier molecules tend to precipitate out first.The major disadvantage of this dating method is that these isotopes also tend to diffuse over time.In these methods, one uses the age of previously determined markers to determine the age of various points in the ice-core. Thus, water evaporating from the ocean it starts off H2(18O) poor. The water molecules composed of H2(18O) evaporate less rapidly and condense more readily then water molecules composed of H2(16O).