They allow us to go back in time and to sample accumulation, air temperature and air chemistry from another time. Slow ice flow at the centre of these ice sheets (near the ice divide) means that the stratigraphy of the snow and ice is preserved. The relationship is consistent and linear over Antarctica. Snow falls over Antarctica and is slowly converted to ice.
Shallow ice cores (100-200 m long) are easier to collect and can cover up to a few hundred years of accumulation, depending on accumulation rates.
If we want to reconstruct past air temperatures, one of the most critical parameters is the age of the ice being analysed.
Fortunately, ice cores preserve annual layers, making it simple to date the ice.
U from dust in the ice matrix can be used to provide an additional core chronology.
The thickness of the annual layers in ice cores can be used to derive a precipitation rate (after correcting for thinning by glacier flow).