Ground Subsidence in Arctic Tundra Unlikely to Trigger Abrupt Thaw

The study sought to understand consequences of a potential positive feedback loop between uneven subsidence and permafrost thaw, which could trigger abrupt and large-scale change in the Arctic. Researchers extended the Advanced Terrestrial Simulator, a site-scale permafrost thermal hydrology model, to represent uneven ground subsidence in polygonal tundra, carbon-rich regions of the Arctic where soils are honeycombed by wedges of ice that express in polygonal patterns. Existing data and new measurements of ground ice content informed simulations of a small catchment near Utqiaġvik, Alaska. Simulations agreed well with multiple types of observations.

Projections indicate 63 cm of bulk subsidence from 2006 to 2100 in the strong-warming Representative Concentration Pathway 8.5 climate. Permafrost thaw as measured by the increase in active layer thickness (ALT)—the thickness of the soil layer that thaws each summer—is accelerated by subsidence, but the effect is relatively small. ALT increases from the current-day value of approximately 50 cm to 180 cm by 2100 when subsidence is included compared to 160 cm when it is neglected. The effect on thaw-exposed soil carbon is larger. Specifically, the mass of soil solids thawing each summer increases by approximately 65% by subsidence. Subsidence also increases runoff efficiency, which will help maintain streamflow but lead to significantly drier tundra conditions. Although uneven subsidence is unlikely to trigger abrupt thaw over large areas, the effects on landscape hydrology and tundra carbon stocks may be significant and should be included in Earth system models.