Geology Reference
In-Depth Information
float. When packed together in large masses, it is called
“pack ice”. Level ice has a fairly flat surface, not affected
by deformation. Deformed ice has its surface affected by
deformation as explained in details in section 2.4.
Seasonal ice is the ice that does not survive summer melt
(i.e., completely melts during summer). Perennial ice has
survived at least one summer melt (SY ice or older). It is
appropriate here to mention that the term “ice class” is
designated also to ships (ice-strengthened or icebreakers)
in order to reflect their strength for navigation through
sea ice. The term “ice class ship” refers to a ship with high
tensile strength keel and hull material. This counters the
term “ice breaker,” which refers to a ship that has heavily
fortified structure.
In addition to ice classes, this section addresses also ice
regimes. The latter refers to a sea ice region that has cer-
tain features based on its geographic location or some
dominant attributes such as ice types, forms, thickness,
mobility, or degrees of deformation. Examples of ice
regimes that are based on geographic locations include
the semienclosed central Arctic, coastal areas, and Sub‐
Arctic estuaries as well as specific regions of operational
or climatic importance. These regimes are described in
terms of their overall ice features. For example, the cen-
tral Arctic features mainly MY ice all year round. The
Sub‐Arctic ice regime features mostly seasonal ice with
medium thickness (0.7-1.2 m) or thicker in winter. A spe-
cific regime such as the Gulf of St. Lawrence in eastern
Canada features seasonal thin FY ice (up to 0.7 m thick)
in February/March period with a rough surface and
highly dynamic nature. The Baltic Sea ice regime has
unique features triggered by the brackish water from
which ice is formed. This includes its low bulk salinity
and porosity [
Granskog et al
., 2006]. The small ice regime
of Storfjord around Svalbard (the Atlantic Ocean) is
characterized by significant temporal variations of ice
cover caused by changes of wind direction pushing the
ice either toward or away from the coast. This triggers
opening of coastal polynyas that are usually covered with
frazil ice [
Dierking
, 2010]. In general, ice information that
is usually used to describe these geographic‐based regimes
includes ice types, thickness, climatology, onset of melt,
and ice duration and variability.
Some ice attributes can also be used to identify an ice
regime. These include fast ice, deformed ice, rough pan-
cake ice, seasonal or perennial ice, polynyas, and so on.
Four ice regimes are discussed in this section: polynyas,
pancake, marginal ice zone and ice edge, and ice of land
origin. Before embarking on these discussions, it is worth
noting that the term “ice regime” should not be confused
with the same term included in the title “Arctic Ice
Regime Shipping System.” The latter is a regulatory
standard being used by ships in the Arctic [
Timco and
Johnston
, 2003]. This system combines the characteristics
of an ice regime based on consistent ice attributes with
ice multipliers that represent the capability of a ship to
navigate in ice‐rich waters. The result of the combination
is an “ice numeral.” This is an index that can be used to
decide if the ship can proceed through the given ice
regime or not.
2.6.1. Criteria of Ice Classification
A few criteria for ice classification have been used in ice
mapping for operational ice monitoring and climate‐
related purposes. They include the following:
1. Ice thickness, which is related to the ice age. This cri-
terion is known as “stage of ice development.” It includes
five major ice types: New ice, Nilas, YI, FY ice, and Old
ice. Subcategories exist within each major category.
2. Ice form, which includes pancake ice, ice floes, ice
breccias, brash ice, fast ice, and anchor ice.
3. Ice concentration, which is defined as the ratio of
ice within a given area of the ocean. It is expressed in
tenth in operational ice charts. The major categories
under this criterion include consolidated ice, compact
ice, very close pack/drift, close pack/drift, open drift,
very open drift, and ice free (open) water.
4. Ice surface form, which includes two major catego-
ries: level (smooth) ice and deformed ice. The deformed
ice includes rafted, ridged, and hummock ice. Other sub‐
categories are included in each category of deformed ice.
An additional surface feature, which is described in terms
of the snow cover, is called sastrugi. It is characterized by
sharp, irregular wavy ridge pattern of drifted snow caused
by wind erosion and deposition.
The sea ice types based on the earlier classification crite-
ria are presented in Tables 2.4-2.7. Table 2.4 includes
classes based on stage of development which implies ice
thickness. Table 2.5 includes classes based on ice forms,
while Table 2.6 includes classes based on ice concentra-
tion. The ice classes based on surface features are shown in
Table 2.7. More information on these types can be found
in the “
Manual of Standard Procedures for Observing and
Reporting Ice Conditions
” or
MANICE
[2005].
2.6.2. Polynyas
A polynya (common US spelling) or polynia (common
UK spelling) is a large area of open water with reduced
ice cover that persists even when atmospheric tempera-
ture is significantly lower than the freezing point. Polynya
is a Russian word which means a “natural ice hole.” It
was adapted by polar explorers to describe navigable
routes through sea ice. This phenomenon develops in
response to oceanic/or the atmosphere forcing. Polynyas
exist in polar regions only and usually keep re‐forming in
the same geographic location every winter and last
between a few weeks and a few months after formation.
