The team were travelling across the West Antarctic Ice Sheet to study snow accumulation. Through analysis of ice cores, scientists learn about glacial-interglacial cycles, changing atmospheric carbon dioxide levels, and climate stability over the last 10,000 years. This picture shows a traversing field camp from December 2010.
The relationship is consistent and linear over Antarctica.
They form bubble-free ice layers, visible in the ice core.
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.
Unfortunately, annual layers become harder to see deeper in the ice core.
Other ways of dating ice cores include geochemisty, layers of ash (tephra), electrical conductivity, and using numerical flow models to understand age-depth relationships.