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.The major disadvantage of this dating method is that these isotopes also tend to diffuse over time.
By comparing the ratios of these isotopes to their nonradioactive counterparts (i.e.
Since volcanic ash is a common atmospheric constituent after an eruption, this is a nice signature to use in comparing calibrated time data and an ice-core of undetermined age. The major diasadvantage of this method is that one must previously know the date of the eruption which is usually not the case.
Furthermore the alkaline precipitants of the ice ages limits this measure to approximately 8000 BC.
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).