clathrate hydrates are solid guest-host com- pounds, formed by small molecules (guests; e.g. N2, O2, cH4 or cO2) trapped in a crystal- line framework (host) of hydrogen-bonded water molecules (chazallon and Kuhs 2002). In natural environments, clathrate hydrates occur in deep-sea sediments and perma- frost (e.g. as methane hydrates). the first direct observations of clathrate hydrates of air (hereinafter, air hydrates) in polar ice were made in 1982 by Shoji and Langway (1982) in the Dye-3 ice core (Greenland) using an optical microscope. Subsequently, air hydrates have been found in all deep ice cores in Greenland and Antarctica (Uchida et al. 2014).