The TLS has a nice article on the memory of ice and a journey to Greenland to see glaciers up close.

Ice is a recording medium and a storage medium. It collects and keeps data for millennia. Unlike our hard disks and terrabyte blocks, which are quickly updated or become outdated, ice has been consistent in its technology over millions of years. Once you know how to read its archive, it is legible almost as far back – as far down – as the ice goes. Trapped air bubbles preserve details of atmospheric composition. The isotopic content of water molecules in the snow records temperature. Impurities in the snow – sulphuric acid, hydrogen peroxide – indicate past volcanic eruptions, pollution levels, biomass burning, or the extent of sea ice and its proximity. Hydrogen peroxide levels show how much sunlight fell upon the snow. To imagine ice as a “medium” in this sense might also be to imagine it as a “medium” in the supernatural sense: a presence permitting communication with the dead and the buried, across gulfs of deep time, through which one might hear distant messages from the Pleistocene.