Permafrost (Subsea)

Subsea permafrost is perennially frozen sediment beneath the seabed on shallow Arctic continental shelves, mostly relict ground that froze on land during low Pleistocene sea levels and was submerged when seas rose in the Holocene. It survives because cold seabed conditions persist, though overlying seawater near minus 1.8 degrees Celsius is warmer than the air that originally froze it, so the permafrost slowly degrades from the top down. Subsea permafrost can cap underlying gas hydrate within its stability zone. Its thaw releases trapped methane, undermines seabed stability for pipelines and structures, and is concentrated on the broad East Siberian and Laptev shelves.