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Other ways of dating ice cores include geochemisty, layers of ash (tephra), electrical conductivity, and using numerical flow models to understand age-depth relationships.
This 19 cm long of GISP2 ice core from 1855 m depth shows annual layers in the ice.
The distribution of melt layers through time is a function of the past climate, and has been used, for example, to show increased melting in the Twentieth Century around the NE Antarctic Peninsula.
It is possible to discern past air temperatures from ice cores.
By looking at past concentrations of greenhouse gasses in layers in ice cores, scientists can calculate how modern amounts of carbon dioxide and methane compare to those of the past, and, essentially, compare past concentrations of greenhouse gasses to temperature. Ice cores have been drilled in ice sheets worldwide, but notably in Greenland and Antarctica[4, 5].
* Solar variation at 65°N due to en: Milankovitch cycles (connected to 18O). Ice core records allow us to generate continuous reconstructions of past climate, going back at least 800,000 years.
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.
For example, melt layers are related to summer temperatures.
More melt layers indicate warmer summer air temperatures.
420,000 years of ice core data from Vostok, Antarctica research station. From bottom to top: * Solar variation at 65°N due to en: Milankovitch cycles (connected to 18O). They spent two nights at each site, first collecting radar data and secondly collecting a 15 m shallow ice core. This schematic cross section of an ice sheet shows an ideal drilling site at the centre of the polar plateau near the ice divide, with ice flowing away from the ice divide in all direction. The large Greenland and Antarctic ice sheets have huge, high plateaux where snow accumulates in an ordered fashion.
The team were travelling across the West Antarctic Ice Sheet to study snow accumulation.