Fun fact. My uncle is a professor of geosciences and goes on expeditions to drill these cores in Antarctica, analyzing their gas contents back at the university. When we'd visit my uncle and his family. My Dad and uncle would commonly head to the university and collect cores which were set to be disposed of and make martinis with 40,000+ yr old ice. The gases have been compressed over time and the weight of the ice, so it would crackle as it melted.