Geology Reference
In-Depth Information
(a)
(b)
20
μ
m
200
μ
m
Figure 2.39
Scanning electron micrograph of a vertical section of a brine pocket at −30 °C in columnar grained
first‐year sea ice with salinity of 4‰ (a) and details of precipitated salt crystals (b) [
Sinha
, 1977a].
2.4. Ice DeFormatIon
Except for landfast ice, which freezes along the coast-
lines or to the seafloor over shallow parts of the conti-
nental shelf, sea ice usually undergoes a complex perpetual
motion at different scales. The mobility of the ice is
caused by one or more of the following geophysical
forces: wind stress, ocean current stress, internal ice resist-
ance, Coriolis force, sea surface tilt, and tidal force. A
brief description of each force (except the tidal force) is
presented in section 10.7.
Thorndike and Colony
[1982]
identified wind as the primary force and ocean current as
the secondary. The motion and interaction of ice floes
result in ice deformation. Deformation assumes different
forms including rafting in the case of thin sheets, break-
ing and compacting of thicker ice sheets, piling of broken
ice pieces to form ridges, openings in consolidated pack
ice, and formation of shear zones. Figure 2.40 shows a
rubble field at the ice surface in the North Water polynya
(north of Baffin Bay) in April 1998. The dark band at the
back is an opening in the pack ice.
The study of ice deformation is important because it
affects key parameters that contribute and serve as indi-
cators to climate variability. These include ice thickness
(when ice sheets overlap or ice blocks pile up), ice concen-
tration (especially when results from divergence of ice
sheets), and to some extent the spatial variability of ice
salinity since brine tends to drain faster from upturned
Figure 2.40
Deformed ice sheet in the North Water polynya,
north of Baffin Bay (photo by M. Shokr).
ice blocks. Ice deformation also contributes to the air‐
water drag coefficients and the momentum transfer from
the ocean currents to the bottom of the ice sheet. Thus, it
is an important input to ice‐ocean‐atmosphere dynamic
models. Sea ice deformation takes several forms at differ-
ent temporal and spatial scales, depending on the stimu-
lating force. Traditionally, ice deformation is considered
at three spatial scales: small, medium, and large.
Small‐scale deformations range from a few hundred
meters to a few kilometers and are manifested in the
forms of fracturing, rafting, ridging, and rough ice sur-
face (rubble fields). They are driven by the wind action
