pattern, but in some years, westerly winds con-
prolonged easterlies transport additional ice into
centrate ice at its eastern barrier of Severnaya
the Taymyr ice massif.
Zemlya and the Taymyr Peninsula, creating a dif-
ficult barrier to navigation.
The East Siberian Sea
Freezeup begins in September in the colder
Of all the Eurasian seas, the East Siberian expe-
northeast Kara and in October in the less saline
riences the least amount of summer melting. On
central region where the Ob' and Yenisey Riv-
average, more than 50% remains ice-covered
ers enter. After that, the intervening region rap-
throughout the summer season. The persistence
idly grows an ice cover that connects the two.
of the ice cover is attributed to cold winter and
The extreme southwest sector, extending 95 to
cool summer air temperatures, prevailing winds,
150 nm eastward from the Kara Gate, normally
ocean currents, a wide continental shelf, and mea-
remains open into November, but with large
ger river inflow.
year-to-year variation (late October to late De-
The East Siberian Sea is the shallowest of the
cember).
Eurasian seas. The broad continental shelf allows
fast ice, averaging 170 to 200 cm thick, to extend as
far as 270 nm outward from the coast. In winter,
The Laptev Sea
Sea-ice distribution in the Laptev is influenced
prevailing southerly winds bring in cold conti-
by cold winter temperatures, southerly winter
nental air, producing a winter mean air tempera-
ture of 30C. These winds also cause weak ice
winds, ocean currents, heavy river inflow, and a
vast continental shelf of very shallow depth. With
conditions and potential navigation lanes at the
the extraordinarily broad continental shelf in this
outer edge of the fast ice as they do in the Kara
region, half of the entire Laptev is less than 50 m
and Laptev Seas.
deep, and south of 76N its depth does not exceed
In summer, the winds shift to northerly, bring-
25 m. Because of these shallow waters, the Laptev
ing in polar air. In addition to cool air tempera-
and the East Siberian Seas have the largest ex-
tures, warming from river inflow is limited. Total
panse of fast ice in the world from January to
river discharge into the East Siberian Sea amounts
June. The fast-ice thickness typically reaches 200
to only 20% of the Kara's total and only 35% of the
cm due to mean midwinter air temperatures of
Laptev's. Ocean currents favor the influx of ice
30C and can grow up to 250 cm thick during
from (rather than its removal to) the Arctic Ocean,
severe winters.
resulting in the permanence of the Ayon massif
Similar to the process previously discussed for
that protrudes into its eastern sector. Winter
the Kara, prevailing southerly winter winds con-
freezeup begins in the north in September and is
tinually push the pack ice northward away from
usually complete by mid-October.
the fast ice, resulting in a nearly permanent lane of
weakness. The amount of old, thick ice found in
The Chukchi Sea (Russian)
the Laptev is limited not only by these winds but
The Russian portion of the Chukchi Sea is al-
also by northward ocean currents. The total area
most totally ice covered from early December to
of summer melt is particularly extensive due to
mid-May. It experiences a large seasonal variation
this reduced presence of old ice. In the western
in ice cover, losing about 80% of its maximum
Laptev, however, the ice drift is southward, and
winter extent during the summer season. The ex-
large masses of ice are deposited along the coast of
tent of its summer ice melt is exceeded only by
Severnaya Zemlya and the Taymyr Peninsula.
that in the Barents. Important factors that influ-
Along with the eastward ice deposition from the
ence sea-ice distribution in the Chukchi are the
Kara Sea, the Vil'kitskogo Strait and the Taymyr
sea's bathymetry, winds, ocean currents, air tem-
coast present a serious challenge to navigation at
peratures, and the presence of Wrangel Island.
Winter mean air temperatures range from 30C
all times of the year.
in the west to 20C in the east due to the inflow of
Many rivers empty into the Laptev, but the Lena
accounts for more than 70% of the total inflow.
relatively warm water from the Bering Sea. Con-
The summer melt pattern is greatly influenced by
sequently, winter mean ice thickness ranges from
this warm water influx. Large areas of open water
180 cm in the west to 130 cm in the east. Because
expand outward from the deltas so that, by the
the continental shelf is less extensive, only a 10- to
end of summer, the Laptev is typically ice-free as
15-km-wide band of fast ice forms along the main-
far north as 77N (only 74N for the western por-
land and the Wrangel Island coast. Ocean currents
tion). Winds are light and variable in summer, but
tend to concentrate old ice from the Arctic into
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