The effect of CO₂ infused ice on the formation and dissociation of CO₂ hydrate

Abstract

CO₂ gas hydrates are crystalline water ice cages around a CO₂ molecule. CO₂ affects global climate change on Earth and a major atmospheric component of the Martian atmosphere. CO₂ hydrates likely have minor effects on terrestrial atmospheric CO₂ , but may be an present in large deposits on Mars. On Earth ice deposits are found in permafrost and glaciers and contain gas bubbles. These gas bubbles may have an effect on hydrate formation and dissociation rates. Such bubbles are also likely present on Mars and may significantly influence gas hydrate fluxes. In this study, CO₂ hydrate formation and dissociation rates were measured experimentally on ultrapure and CO₂ infused water ice (ice containing previously trapped CO₂ gas bubbles). Overall, increasing pressure and temperature increased hydrate formation rates. Formation and dissociation rates both increased significantly in infused ice experiments as did the overall amount of hydrate formed. The bubbles formed during freezing of the infused ice likely provided more surface area for hydrate nucleation, increasing the rate of formation. Dissociation rates were higher in infused ice compared to ultrapure ice likely due to the larger amount of hydrate formed. Investigation of CO₂ hydrate formation from infused ice in hand sample revealed distinctive hydrate and ice layers. Most of the hydrate was observed to form in the first four hours, which agrees with other experimental data. During the dissociation of the hand sample experiments, a new opaque layer was observed forming after 5-10 minutes that is possibly hydrate. This could represent hydrate formation at room temperature and pressure through remobilization and clathration of CO₂ in the ice.