Fluids migration through permafrost and the pool of greenhouse gases in frozen soils

Abstract:

Most of methane (CH₄) and carbon dioxide (CO₂) emissions originate from biodegradation of organic matter from soils and degrading permafrost in the Arctic. However, there is some evidence on the activity of geological sources in the Arctic, and little understanding on the pathways of migration of gaseous fluids through the porous mineral matrix filled with ice. We estimated the winter storage of the greenhouse gases and the effect of geological factors on an oil-and-gas field by statistical analysis of a geodatabase, which combined field gas survey of frozen soils, subsurface sounding, and remote sensing data. Frozen soils represented a huge storage of 0.016 g CH₄ m^-3 and 11.5 g CO₂ m^-3. Sites of microseeps, recognized by isolated anomalies of helium, had 30 % higher CH₄ concentrations. Lineaments marking margins of tectonic blocks were estimated to have 300 % higher CH₄ concentrations. High concentrations of propane and ethane pointed at the contribution of leakages from hydrocarbon-bearing beds on 95 % of 130 km² of the study area. However, the filtration through permafrost is questioned, despite of the links with permafrost thickness, and high CO₂ concentration likely pointing at CH₄ oxidation. Landscapes controlled CO₂ concentration and hid the geological effects on CH₄.