Temperature changes and thaw of permafrost adjacent to Richards Island, Mackenzie Delta, N.W.T.

Abstract

Thawing of ice-bonded sediment below the sea floor accompanies sea-level rise and shoreline retreat along the Beaufort Sea coast. The rate of thaw is primarily controlled by the warm spring and summer discharge of the Mackenzie River, which affects sea-bottom temperatures to water depths of 10–20 m. The intensity of the warming at any one location decreases with depth until continuous sub-0 °C temperatures are encountered. Sea-level rise eventually brings the sea floor into the cold sea-water zone and thawing stops. Therefore thawing is also controlled by the residence time in the warm zone. Sedimentation or scouring can, respectively, slow or accelerate the increase in water depth and thereby modify the rate of thaw progression. This, combined with changes in the rate of coastal retreat, can produce a subbottom frost table with considerable relief. In the extreme, ice bonding within a few metres of the sea floor can be explained by accelerated submergence.