Subsea Permafrost

Subsea permafrost is perennially frozen seabed sediment on shallow Arctic shelves, largely relict terrestrial permafrost that froze during Pleistocene glacial low stands and was flooded as sea level rose in the Holocene. Submerged under seawater near minus 1.8 degrees Celsius, warmer than the air that froze it, it degrades slowly from above and is thinnest where inundation was earliest. It acts as a seal over methane in the underlying hydrate stability zone, so thaw opens pathways for methane escape to the water column and atmosphere. The largest extent lies beneath the East Siberian Arctic Shelf, where it raises concerns for seabed engineering and carbon feedbacks.