Geology Reference
In-Depth Information
Ice arch
Robenson
Channel
Ice arch
Ellesmere
Island
Greenland
Possible ice
arch location
Polynyas
Smith
Sound
Baffin Bay
Figure 2.68 The boundary of the North Water Polynya shown
by the dashed line. The background image is from the
QuikSCAT scatterometer acquired on January 30, 2009. An ice
arch was formed in that year, and its location is indicated by
the arrow at the top. The other possible location of the arch
(did not exist in that year) is at the southern end of the Kane
Basin, as marked by the lower arrow.
Figure 2.67 AVHRR image of the North Water polynya area
in April 1998. Two polynyas are shown in the dark areas, the
bigger (top) is the North Water Polynya and the smaller (left)
is Lancaster Sound Polynya. The ice arch is visible in both
polynyas. The arch is usually formed when ice is drifted
through a narrow channel.
in the middle of the image and the Lancaster Sound pol-
ynya at the left side. While the NOW may be formed with
or without the presence of the arch, the Lancaster Sound
polynya is formed and maintained only when the arch
is formed. Since polynyas are regions of high ice pro-
duction and reproduction, they are considered to be a
significant source of brine flux to the ocean.
Since NOW is the largest recurring polynya in the
Arctic, a brief description of its formation, recurrence,
and ice cover is presented in the following. A map show-
ing its border and the surrounding area is presented in
Figure  2.68. Its boundary encloses an area of approxi-
mately 80,000 km 2 , comprising OW, YI, and FY ice
[ Dunbar , 1969]. NOW is mostly a latent heat polynya
generated through the actions of katabatic wind and to
a lesser extent ocean currents [ Ingram et al ., 2002]. It is
usually formed by mid‐winter although the formation
was observed as early as late November in a few years
[ Shokr and Agnew , 2013]. An ice arch is usually formed
either at the northern end of Robeson Channel as
shown in the figure or at the constriction points between
Ellesmere Island and Greenland at the southern end of
Kane Basin. It prevents further drift of perennial ice
from the Arctic Basin southward. Based on analysis
of  satellite imagery of surface brightness temperature
between 1979 and 1996, Barber et  al . [2001] suggested
that during the 1980s the formation of the arch was
more regular, whereas in the 1990s the formation was
less regular with a tendency to form later and break ear-
lier. Shokr and Dabboor [2013] obtained data on the
extent of YI, FYI, and OW in the polynya in each year
during the period from 2002 to 2009. During this period,
the ice arch was formed two times at the southern end
of Kane Basin (February 25, 2003 and February 16,
2006) and three times at Robeson Channel (November
11, 2004; March 12, 2008; and January 18, 2009). It was
not formed in 2003-2004 and 2006-2007, but the pol-
ynya still formed. In 1998, it was formed at the southern
end of Kane Basin.
The NOW polynya features mainly FY ice with less
area of YI and OW in addition to fragments of MY ice.
YI is localized mostly in the vicinity of the ice arch
(if formed south of Kane Basin) with more distribution
in the west side of the polynya. The coastal areas at
the  two sides of the polynya are usually composed of
landfast ice, which can be MY, especially in narrow fjords.
Shokr and Dabboor [2013] show the daily evolution of the
areas of OW, YI, and the combined FY and MY ice from
December until end of April (Figure 2.69). On the aver-
age, YI occupies 15% of the total area of the polynya
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