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bodies is useful in determining recent water migration into permafrost (Burn and Michel,
1988; Michel and Fritz, 1982), the study of seasonal-frost mounds (French and Guglielmin,
2000; Pollard and French, 1984), or recent ice-wedge growth (Lewkowicz, 1994).
It is clear, therefore, that isotopic compositional differences in groundwater and ground
ice can assist in the interpretation of the history and stability of permafrost, such as
whether permafrost grew in open or closed systems, in the recognition of thaw uncon-
formities, in understanding certain geomorphic processes, and in the characterization of
ground ice bodies.
7.4.6. Cryostratigraphy and Past Environments
Cryostratigraphic observations from the lowlands of the Western Canadian Arctic indi-
cate that during the early Holocene the climate ameliorated, causing permafrost to
partially thaw but to then subsequently refreeze towards the end of the Holocene. The
evidence consists of a widespread paleo-thaw layer (Burn 1988, 1997; French et al., 1986;
Harry et al., 1988; Murton and French 1994). It can be recognized by distinct cryostruc-
tural contrasts and, in places, by truncated ice bodies. A good example is from Pullen
Island (see Figure 7.3), where the regional hypsithermal thaw unconformity (a “paleo-
thaw layer”) occurs at a depth of 125-150 cm. This is approximately 2.5 times thicker than
the present active layer. Radiocarbon dating of organic material just above the unconform-
ity suggests thaw was greatest about 8.0-9.0 ka.
This regional thaw unconformity in the Western Arctic can be used to infer the rela-
tionship between permafrost and past climate by application of the Stefan equation (see
Chapter 5). If one assumes that an increase in the active layer is the result of summer
thaw and that thaw is linked to thawing degree-days (TDD), the Stefan equation indicates
that a doubling of active-layer thickness corresponds to a fourfold increase in thawing
index and that an active layer 2.5 times as thick as today implies an increase in the thawing
factor by 6.25.
This type of analysis can be applied to the climatic records from fi ve settlements that
represent a north-south transect, covering 16 degrees of latitude, across the Western
Canadian Arctic (Table 7.7). From north to south, the fi ve localities each typically
record thawing indices of approximately 1900, 1200, 800, 400, and 300 degree-days per
year, respectively. The thickness of the active layer at each locality is approximately
Table 7.7. Data showing average active-layer depths, the depth of the Early Holocene thaw
unconformity (where recognized), typical annual thawing degree-days, and bio-climatic zonations for
fi ve localities in the Western and High Arctic of Canada.
Locality
Latitude
Thawing
Active
Early-Holocene
Ecozone
Degree-days
Layer (cm)
thaw
(°C)
unconformity
Whitehorse
61° N
1900
125-150
Boreal forest
Inuvik
68° N
1200
100
Treeline
Tuktoyaktuk
69° N
800
50
125-150*
Tundra
Sachs Harbour
72° N
400
30-50
Tundra
Eastern Melville Island
77° N
300
25-50
113**
Polar semi-desert
* Thaw unconformity at 125-150 cm depth corresponds to
1800 thawing degree-days.
** Thaw unconformity at 113 cm depth corresponds to
600 thawing degree-days.
Sources: French et al. (1986), Burn (1998a).
 
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