Geology Reference
In-Depth Information
Table 3.2 .
Annual mean air, ground, and lake-bottom temperatures (2000-2004) at sites in
the Mackenzie Delta region, Canada, that span the tundra-taiga (forest) transition zone.
Ecotone
Locality
Temperature (°C)
Annual
Summer
Winter
Ground
mean air
air
air
temperature
temperature
temperature
temperature
Southern Arctic
Illisarvik
−
12.5
−
5.6
(tundra)
Tuktoyaktuk
−
9.0
9.9
−
27.0
To dd L a ke
(10 m depth)
3.4
(littoral bench)
−
2.0
Taiga Plain
Inuvik
−
6.7
13.4
−
25.5
(forest)
Inuvik peat lands
−
1.2
Dempster Lake
5.7
(3 m depth)
Source: Burn (2005). Reproduced by permission of John Wiley & Sons Ltd.
of Canada (Table 3.2). Collectively, the sites span the tundra-taiga (forest) boundary. This
is a zone 50-150 km in extent that extends southwards from the arctic coast to beyond the
treeline. Over this area the mean annual air temperature varies by 6 °C, there is a differ-
ence between air and 3 m lake-water depth temperature of
∼
18 °C, and the range between
maximum and minimum air temperature is
40 °C. Clearly, the use of average annual or
monthly air temperatures values to describe periglacial climatic conditions is a gross
oversimplifi cation.
At a more fundamental level, the annual change of state of near-surface material from
its frozen to thawed state, and vice-versa, is of specifi c interest to periglacial geomorphol-
ogy. This is now discussed briefl y in the context of n-factors.
∼
3.3.1. The n-Factor
V. J. Lunardini (1978) fi rst described n-factors as transfer functions between air and
ground surface temperatures. Seasonal values can then be multiplied with air tempera-
ture indices to obtain suitable approximations for ground temperature. For example,
some typical n-factor values assigned to different vegetation types in central Alaska are
presented in Table 3.3. Similar values have been successfully applied to the variability
of air and soil-surface temperatures in a number of localities (Hinkel et al., 1997;
Karunaratne and Burn, 2003, 2004; Klene et al., 2001) but calculation of n-factors for
the thaw season is diffi cult (Taylor, 1995, 2000). This is illustrated by data from fi ve sites
in the boreal forest in central Yukon Territory, Canada (Table 3.4). As might be expected,
variation in n-factor over the winter seasons was largely the result of differences in snow
depth. However, in summer, as the thaw front penetrated below the depth of diurnal
temperature fl uctuation, the air and ground surface temperatures converged. Because
the rate of thaw penetration is governed by soil-thermal diffusivity, this suggests that
summer n-factors vary directly with soil-thermal diffusivity.
