Geology Reference
In-Depth Information
Salinity (‰)
Salinity (‰)
1.00
0
81
6
0
816
Snow
Surface 81 /82
0
Snow
82 /83
Surface
Surface melt
FY ice
1.00
SY ice
"
FY ice
"
2.00
Bot tom
melt
3.00
Year 1
Growth
Year 2
Growth
Melt
4.00
S
NJ
MMJ
SN J
MMJ
1981
1982
1983
Figure 2.64
Ice composition and thickness, along with snow depth in Mould Bay, Canadian western Arctic from
September 1981 to mid‐May 1983. Re‐growth of ice (referred to as FY) under the SY ice after September 1982 is
also shown [
Bjerkelund et al
., 1985].
history is shown in Figure 2.64. FY ice grew during the
winter of 1981-1982 to a maximum thickness of 2.17 m
with 0.65 m of overlaid snow by mid‐June 1982, when
surface melt started. By the end of June, the snow had
melted completely and melt ponds had covered 90% of
the surface. This area decreased shortly thereafter to less
than 50%. By the end of August 1982, the ice thickness
attained a minimum of 0.7 m, by surface ablation and
bottom melt. Re‐growth of ice at the bottom of SY ice
started sometime in September 1982. The growth rate
was similar to that of the original FY ice in the previous
year. Snow also started to accumulate on the SY ice sur-
face. The salinity profile of the FY ice in May of the first
winter (1981/1982) depicts the familiar C‐shape. The
remarkable observation, however, is made in the salinity
profile obtained in April 1982. There is sharp increase of
salinity across the interface between the SY and the
underlying newer FY ice. Salinity jumps from 0 to 3.7‰
over a short vertical distance of 0.05 m. The fabric of the
columnar ice growth is preserved across the interface as
shown in Figure 5.28.
As mentioned before, sea ice tends to age in the Arctic
more than it does in the Antarctic. Arctic Ocean is essen-
tially land‐locked so that sea ice usually remains in the
Arctic basin for several years before it is drifted south
through the routes shown in Figure 2.52. Ice formed in
the central Arctic may remain circling in the basin for
7-10 years, driven by the Beaufort Sea Gyre system,
before it drifts south. By contrast, in the Antarctic there
is no land boundary that borders the north of the ocean
from the coast of Antarctica along about 60° S. The sea
ice is free to drift northward into warmer open water
where it melts. The motion is driven by the ocean cur-
rents and atmospheric circulation. The Antarctic
ice cover is, therefore, highly seasonal, with a relatively
lower thickness (up to 1 m) compared to the seasonal ice
in the Arctic. Most of the aged MY ice in the Antarctic
(about 80%) is carried by the Weddell Gyre (a clockwise
circulating current in the eastern side of the Antarctic
Peninsula) and accumulate at the west of the Weddell
Sea. For many years, this gyre has been responsible for
trapping sea ice in that location. Other MY ice exists
in isolated embayment at other locations around the
Antarctica coast. Eventually, the ocean current trans-
ports the ice further north where it dissipates into the
ocean and melts.
2.6. Ice classes anD Ice reGImes
Different sets of ice classes are based on different crite-
ria. The most commonly used criterion is thickness‐based
where each ice type is associated with a range of ice
thickness. Thickness is associated with age, therefore
this criterion is also considered to be age‐based. It has
been adopted by the World Meteorological Organization
[
WMO
, 1985] and consequently used to classify ice types
in operational ice charts. Other criteria are introduced in
this section. In addition to the ice classification systems
that employ a number of categories in each system, there
are three sets of dual classes; fast ice versus floating ice,
level ice versus deformed ice, and seasonal ice versus per-
ennial ice. Fast ice refers to ice fastened to the shore or
grounded to the sea floor (only if the water is shallow;
usually <2 m thick). Floating ice, is any form of ice free to
