Abstract

The occurrence and magnitude of natural fossil methane (CH4) emissions in the Arctic are poorly known. Emission of geologic CH4, a potent greenhouse gas, originating beneath permafrost is of particular interest due to the potential for positive feedback to climate warming, whereby accelerated permafrost thaw releases permafrost-trapped CH4 in a future warmer climate. The development of through-going taliks in Arctic lakes overlying hydrocarbon reservoirs is one mechanism of releasing geologically sourced, subpermafrost CH4. Here we use novel gas flux measurements, geophysical observations of the subsurface, shallow sediment coring, high-resolution bathymetry measurements, and lake water chemistry measurements to produce a synoptic survey of the gas vent system in Esieh Lake, a northwest Alaska lake with exceedingly large geologic CH4 seep emissions. We find that microbially produced fossil CH4 is being vented though a narrow thaw conduit below Esieh Lake through pockmarks on the lake bottom. This is one of the highest flux geologic CH4 seep fields known in the terrestrial environment and potentially the highest flux single methane seep. The poleward retreat of continuous permafrost may have implications for more subcap CH4 release with increased permafrost thaw.