Rate of permafrost degradation in peatlands.

摘要

Due to the insulating properties of dry peat, permafrost at its southern limit occurs mainly in peatlands, where it is found in raised mounds or plateaus because of the expansion of freezing water. The dry peat on the surfaces of plateaus protects the permafrost from summer heat. However, because peat forms in wet conditions, peat plateaus are usually surrounded by wetlands, and often by standing water. The standing water acts as a heat conductor, causing the permafrost core to melt From the sides. Peat plateaus have been found to undergo cycles of aggradation and collapse. Fire is a major trigger for peat plateau collapse because it can consume the insulating peat.;The peat plateau surface provides a suitable habitat for tree growth. Trees on the subsiding plateau edges die when their roots drown in the wetland. The dead trees provide a record of the location of the plateau edge over time because their dates of death, determined by crossdating, indicate when they were deposited into the water.;Study sites were at Hotchkiss (57