Maintaining ice-core quality through the brittle ice zone (BIZ) remains challenging for polar ice-core studies. At depth, increasing ice overburden pressurizes trapped air bubbles, causing fracture of cores upon exposure to atmospheric pressure. Fractured ice cores degrade analyses, reducing resolution and causing contamination. BIZ encounters at 18 sites across the Greenland, West and East Antarctic ice sheets are documented. The BIZ begins at a mean depth of 545 ± 162 m (1 standard deviation), extending to depths where ductile clathrate ice is reached: an average of 1132 ± 178 m depth. Ice ages in this zone vary with snow accumulation rate and ice thickness, beginning as young as 2 ka BP at Dye-3, Greenland, affecting ice >160 ka BP in age at Taylor Dome, Antarctica, and compromising up to 90% of retrieved samples at intermediate-depth sites. Effects of pressure and temperature on the BIZ are explored using modeled firn-column overburden pressure and borehole temperatures, revealing complex associations between firn densification and BIZ depth, and qualitatively supporting expected thinning of the BIZ at low ice temperatures due to shallower clathrate stability. Mitigating techniques for drilling, transport, sampling and analysis of brittle ice cores are also discussed.

Cryo-Raman tomography allows us, for the first time, to determine accurate morphologies and volumes of natural air hydrates in Antarctic ice cores. The measurements show complex growth structures that are not accounted for by the available models of hydrate formation.

We apply new phase-equilibrium data of air-clathrate hydrates to the distribution of air hydrates in deep ice sheets to better understand their nucleation conditions. By comparing the depths at which the hydrates first appear to the phase-equilibrium condition, we estimated the critical size of an air-hydrate nucleus in an ice sheet to be ~50 nm. The estimated energy barrier for nucleation, based on the temperature dependence of supersaturation, is much smaller than that estimated previously for the pure ice system. Thus, the bubble surface may either act as a type of heterogeneous nucleus, or contain heterogeneous nuclei, for hydrate formation. Competition between nucleation-promotion and nucleation-inhibition factors may increase variation in nucleation rates, resulting in variation of the depth range of the bubble–hydrate transition zones.

The physical behaviour of methane and carbon dioxide clathrate hydrates, specific crystallographic ice crystals are of major importance for the earth and may control the stability of gases in many astrophysical bodies such as the planets, comets and possibly interstellar grains. Such models claim they provide an alternative trapping mechanism modifying the absolute and relative composition of icy bodies and can be at the source of late time injection of gaseous species in planetary atmospheres. However, there is a clear need to detect them directly. We provide in this study the laboratory recorded signatures of clathrate hydrates in the near to mid-infrared for astrophysical remote detection. These laboratory experiments will in a near future allow to follow the kinetic formation by diffusion in dedicated experiments, another important step to implement, to understand and model their possible presence in space.