The permafrost regime in the Mackenzie Delta, Beaufort Sea region, N.W.T. and its significance to the reconstruction of the palaeoclimatic history

Abstract

AbstractObserved depths to the base of the ice‐bearing permafrost (!BPF) as determined from geophysical well‐log and survey information in the Mackenzie Delta and offshore Beaufort Sea continental shelf show significant variation. Depths range from over 700m beneath the northeastern portion of Richards Island and the adjacent offshore region to the north, to less than 100m in the modern Mackenzie Delta and offshore Mackenzie Bay regions. Along the Tuktoyaktuk Peninsula, permafrost thicknesses exceed 600m but tend to thin to less than 100m in a southeasterly direction.The wide variation in the thickness and distribution of permafrost is due in part to differences in the subsurface deltaic lithologies and to the complexity of the past surface temperature history, exhibited, for example, by fluctuations of the mean annual ground temperature. Geological cross‐sections showing variation in the Tertiary and Upper Cretaceous deltaic sequences indicate a good correlation with the permafrost distribution. In particular, where the sand and gravel units of the Iperk and Kugmallit Sequences predominate, permafrost is thick owing to the high thermal conductivities of the ice‐rich sediments. Conversely, where the low thermal conductivity shales and mudstones of the Richards Sequence are present, permafrost is accordingly thinner.Numerical models of permafrost aggradation in the Mackenzie Delta region suggest that Early and Late Wisconsinan surface temperatures were of the order −18°C. A mid‐Wisconsinan rise in temperature to approximately −8°C, similar to mean surface temperature today, is also indicated. This proposed palaeoclimate is sufficient to account for the observed maximum permafrost thicknesses in the region.