Geoscience Reference
In-Depth Information
mass balance of the ice sheet is now clearly negative, contributing to sea
level rise.
Polar desert, the most extreme form of tundra, is widespread in
the Canadian Arctic Archipelago, the unglaciated parts of northern
Greenland, and the islands of the Siberian Arctic. Mean annual
temperatures are well below freezing and only exceed the freezing point
for one or two summer months. Annual precipitation is low, typically with
a summer or early autumn maximum. Topoclimates and microclimates
are often strongly developed, which can be associated with extremely low
minimum winter temperatures. By comparison, local topography in some
regions can give rise to foehn conditions and spells of unexpectedly high
summer temperatures.
Maritime conditions are well expressed in the Atlantic sector. These
regions are characterized by extensive cloudiness year round, high
humidity and a fairly small annual temperature range. Precipitation in
many maritime areas is quite high. In accord with seasonality in the
strength of the North Atlantic storm track, there is a general cold season
maximum. Maritime conditions also characterize much of the Bering Sea
region. Areas along the Beaufort and Chukchi sea coasts are sometimes
considered maritime, but conditions are really closer to those for polar
desert.
Over the central Arctic Ocean, mean winter air temperatures are
typically −30°C to −33°C, contrasting with July, when - because of the
melting ice surface - mean air temperature tend to hover around the
freezing point. Precipitation is generally low, with a late-summer to early-
autumn maximum, corresponding to maximum cyclone activity. August
cloud cover is near 90 percent.
8.1
The Greenland Ice Sheet
8.1.1
General Features
The Greenland ice sheet (
Figure 8.1
) is by far the largest terrestrial ice mass
in the Arctic and is the second largest in the world (following the Antarctic ice
sheet). The ice sheet covers an area of 1.71 × 10
6
km
2
. Other glaciers and ice
caps on Greenland cover a further 0.49 × 10
6
km
2
(
Table 2.1
). The ice sheet
reaches a maximum elevation of just more than 3,200 m at Summit (72.6°N,
37.5°W). A secondary elevation maximum on the southern part of the ice sheet
rises to about 2,800 m. The surface slope over most of the Greenland ice sheet is
barely 1 degree, but is much greater at the margins. The margins of the ice sheet
are also characterized by numerous fiords and associated ice streams and valley
glaciers that drain the ice sheet. Greenland is the source of most of the icebergs
found in the North Atlantic. The maximum thickness of the ice sheet has been
