Geology Reference
In-Depth Information
Table 2.8
Monthly average surface temperatures over North Water Polynya in the Arctic (°C) (data extracted from the database
of the National Snow and Ice Data Center (NSIDC).
December
January
February
March
April
2002-2003
−27.66
−28.91
−29.25
−29.45
−15.48
2003-2004
−27.63
−29.16
−29.82
−26.11
−16.41
2004-2005
−15.30
−17.09
−14.09
−27.66
−17.25
2005-2006
−15.16
−13.70
−20.40
−23.21
−11.56
2006-2007
−20.98
−23.21
−26.23
−19.67
−9.99
2007-2008
−21.14
−19.14
−23.69
−25.03
−16.08
2008-2009
−22.14
−21.08
−24.74
−24.52
2.6.3. Pancake Ice Regime
During development of frazil ice turbulence will not
allow consolidation of the herded frazil crystals into
an extensive sheet of Nilas. Instead, it causes frazil to
undergo cyclic compression following the wave action.
When compressed, the herded crystals may bond with
each other and when in‐between water freezes a pancake
ice disc is formed. As mentioned in section 2.2.1, a pan-
cake ice piece is predominantly circular in shape with typi-
cal diameter between 0.3 and 3 m, and they can grow up to
0.1 m in thickness. The pieces are band together during the
early growth stage. A pancake ice regime is a wide area
covered with adjacent or overlapping pancakes. Pancake is
a surface feature, but the ice can grow vertically under it
(ice congelation) to any depth. Pancake ice regimes of FY
thick ice (>2 m thick) in the Arctic was observed and veri-
fied by the authors using satellite radar imagery. It is com-
mon for fully grown Arctic FY ice with pancake surface to
be covered with snow. In this case, its ragged appearance
will not be visible but can only be revealed using imaging
radar data (ragged surface produces high backscatter).
The pancake discs may start as slush before solidifica-
tion to form an ice floe (Figure 2.70). In addition to the
circular shape of the discs, their mobility and collision
give rise to their raised edges. This is one expression of
surface roughness of a pancake ice regime. The other
expression is the overlap of adjacent pieces which is shown
in the photograph in Figure 2.71. It depicts a snow‐free
surface of FY thin ice (0.38 m thick) in the Labrador Sea
in March 1994. Rafting of pancake ice pieces with their
edges protruding upward increases the percentage of OW
available for additional frazil ice production in the water.
With more frazil ice present, further pancake production
occurs, followed by rafting and continued frazil ice pro-
duction. This positive feedback cycle continues to expand
the areal coverage of the pancake ice field. This process
slows down as the ice becomes thicker and can no longer
overlap (thickness >0.2 m, depending on wind velocity).
Formation of pancake ice field is triggered by a mini-
mum level of surface wave action. Since more of these
actions are found in the marginal ice zones and near ice
Figure 2.70
Formation of pancake in frazil/slush ice medium.
Note the raised rims of pancakes.
though the ratio varies between 0 and 35% in the studied
year (2002-2009). It tends to decrease after November
and increase during April. YI occupies almost exactly
twice as much area as the OW except in 2009 when it
occupied slightly higher than one‐third of the OW area.
The high correlation between YI and OW areas is indi-
cated by the correlation coefficients (CCs) shown in
Figure 2.69 for each year. The average correlation coeffi-
cient for all years is 0.85. On the other hand, the atmos-
pheric temperature does not seem to affect the presence
of YI in the polynya. This can be seen by taking into
consideration the monthly averaged temperature data
presented in Table 2.8. It is interesting to note that the
relatively high temperatures during December 2004-
February 2005 (around −16°C) and again in January
2006 (−13.7°C) are associated with virtually zero YI and
OW area (Figure 2.68). It appears also from this data set
that the ice arch is not the determining factor for the pol-
ynya formation. It acts only to maintain the polynya
while oceanic and meteorological parameters are the key
factors for its formation.
