Influence of permafrost thaw on an extreme geologic methane seep

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.