Geology Reference
In-Depth Information
wide fjord in Mould Bay, Canadian western Arctic dur-
ing 1981-1982 are given in Chapter 5.
Snow depth varies significantly between different
regions and at different times. Moreover, snow depth has
been reported to be greater on multiyear ice (MYI) than
firstyear ice (FYI). For example, in the MIZEX'84 experi-
ment snow depth on FYI was found to be 80 mm on aver-
age and never exceeded 0.20 m, while it averaged 0.40 m
on MYI [ Tucker et  al., 1987]. A similar observation is
made in Shokr and Barber [1994] from the measurements
during the first experiment in the SIMMS program
(between 15 May and 8 June, 1990) when they found that
the average snow depth was 20.5 and 36.2 cm on FY ice
and MY ice, respectively, with higher standard deviation
from MY ice. This is due to the undulating topography of
the MY ice surface. Tucker et al. [1987] related the thicker
snow cover on MY ice to the ice thickness. They sug-
gested that, for thinner ice types such as FY ice, more heat
is conducted from the ocean to the ice surface and there-
fore snow would be more susceptible to loss by sublima-
tion. In the AIDJEX experiment, snow depth on MYI
averaged 10 cm on hummocks and 30 cm on depressions
(melt ponds). Warren et al. [1999] analyzed data from sev-
eral Canadian weather stations listed in Table 1.1 that
operated for 37 years from 1954 to 1991 in the Arctic to
explore the temporal evolution of snow on ice. They con-
cluded that the ice remains mostly snow‐free during
August but snow starts to accumulate rapidly in September
and October. It continues to accumulate though moder-
ately in November and very slowly in December and
January. It accumulates moderately again from February
to May. The Chukchi Sea region shows a steadier accu-
mulation throughout the autumn, winter, and spring. The
average snow depth on the MY ice reaches a maximum of
34 cm in May. The average snow density increases with
time throughout the snow accumulation season, averag-
ing 300 kg/m 3 , with little geographical variation.
Snow cover on Antarctic sea ice is usually deeper than
that on ice in the Arctic. Jefferies et  al. [1994] observed
more than a meter of snow in some regions in the
Antarctic. In a study to compare differences between
snow cover over FY and MY ice in the Weddell Sea,
Antarctic, Nicolaus et  al. [2009] measured snow proper-
ties and thickness on level ice. They found that snow on
MY ice was thicker, colder, denser, and more layered than
on FY ice. Snow metamorphism, however, was similar
between the two ice types because it depended more on
surface heat fluxes and less on underground properties.
The point sampling measurements of snow thickness
can be reliable only for examining spatial distribution of
snow over a small area and for short periods. The alterna-
tive is to use (1) physical models to estimate the evolution
of the snow distribution or (2) remote sensing observa-
tions to retrieve snow depth and other properties. Data
from using the second approach are presented in sec-
tion 10.6. A model to estimate the evolution of the snow
distribution, called the snow model has been developed
and used to simulate evolution of snow over land using
input from meteorological and vegetation cover data
[ Liston and Elder, 2006]. Iacozza and Barber [2010] applied
this model to sea ice and compared results against in
situ  measurements of snow on fast ice in Tuktoyuktuk,
Nortwest Territory (NWT), Canada. They found a sig-
nificant disagreement between observed distribution and
model output, which was attributed to meteorological
data being incomplete or inaccurate.
2.2.4.3. Effect of Oceanic Heat Flux
The effect of the upwelling oceanic heat flux ( F w ) from
the deeper water to the ice‐water interface is neglected in
equations (2.9) and (2.18). Without this flux, the ice will
grow as long as the atmospheric temperature continues to
be below the freezing point of the seawater. However, in
the presence of this flux, the ice growth may be hindered.
This amount of heat is usually small in most regions of
the Arctic (around a few W/m 2 ) as indicated by Steele and
Flato [2000] , so it can indeed be neglected in the heat bal-
ance equation. In the Antarctic, where the upwelling con-
vective heat flow from the deep ocean can reach several
tens of W/m 2 [ McPhee et al., 1998], the oceanic heat flux
cannot be neglected. That partly explains the slower ice
growth in the Antarctic where ice has been found to be
generally thinner compared to the Arctic.
In extreme cases oceanic heat flux may impede or pre-
vent ice formation, even in areas of cold atmospheric
temperatures. It also causes melting of the ice bottom
during summer or at least slowed down ice growth later
in the fall [ Yu et al., 2004]. But perhaps the most striking
phenomenon caused by oceanic heat flux is what is
known as the “sensible heat polynya.” Here, the upwelling
warm water is so strong that it causes the ice to be signi-
ficantly thinner or impossible to form because the water
surface temperature keeps rising to offset the colder
atmospheric temperature. Using a one‐dimensional ther-
modynamic model of sea ice, Maykut and Untersteiner
[1971] found that ice thickness is sensitive to even small
changes in the oceanic heat flux.
2.2.4.4. Effect of Surface Ablation
While ice thickness is expected to increase as it grows at
the bottom, the total thickness may, actually, decrease
slightly due to surface ablation. This is triggered by sub-
limation, a process of solid to vapour transformation
(directly related to the high‐temperature state of ice, being
close to the melting point) or surface melt or both. As
for sublimation, the air temperature, humidity, and wind
velocity are the driving factors. Surface melting, on the
other hand, is caused by a rise in atmospheric temperature
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