METHANE DISTRIBUTION IN PERMAFROST: EVIDENCE FOR AN INTERPORE PRESSURE METHANE HYDRATE

摘要

We report on studies of intergranular methane found in near-surface permafrost in northeastern Siberia, located outside oil and gas producing regions. This methane occurs in discrete layers at various depths, with negligible lithostatic pressure. Discontinuities in the methane distribution indicate that the methane is in a bound form and not able to diffuse. Upon thawing, the methane is released abruptly, in a phase change with associated enthalpy. These two facts suggests that the methane is held in a clathrate form within the sediments. Samples from cores containing deep methane hydrate which were degassed at low pressure while still frozen also exhibited this release of bound methane upon thawing. We conclude that, when temperatures are below freezing, methane hydrate can form at atmospheric pressure independently of high pressure forms of hydrate. The presence of discrete horizons containing methane in the permafrost provides a record of changing temperature and water conditions at the surface and their effect on anaerobic microbial activity. Unlike the deep high-pressure methane hydrates, this reservoir of bound methane could be released by warming in the polar regions.