Geoscience Reference
In-Depth Information
geothermal heat flow, the bottom water temperature, salinity and the freezing of
bottom sediments by grounded landfast ice and grounded keels. Seaward of the sub-
marine permafrost, there may also be a narrow zone of seasonally frozen submarine
sediments. A. Gavrilov (
2001
) proposes that most submarine permafrost represents
relic strata formed during glacial episodes of the late Pleistocene. The upper ice-rich
strata would have been thermally abraded during sea level rises such as during the
Holocene. In the Beaufort Sea, the permafrost upper boundary varies between the
seabed and 100-150 m and its base may lie as deep as 600-900 m. In the Laptev Sea
region where the terrestrial permafrost is 500-800 m thick, ice-bonded permafrost
offshore is relic (Hubberten and Romanovskii,
2001
). It is continuous to the −65 m
water depth and discontinuous to −100 to −120 m depth. The maximum submarine
permafrost thickness is about 500 m north of Kotelny Island.
The ice content of permafrost is difficult to determine quantitatively, owing to its
spatial variability and the limited number of boreholes allowing for analysis. Only
about 10 percent of the terrestrial permafrost area is “ice rich.” The IPA map shows
that ice-rich permafrost, with an ice content of less than 20 percent by volume in
the upper 10-20 m of the ground, is widespread in the coastal Siberian lowlands of
Yamal (around the Ob estuary) and east of the Lena delta in Yakutia.
Permafrost temperatures have been monitored in Alaska, Russia, and Canada
since the middle of twentieth century. These data document a general pattern of
warming permafrost in Alaska, northwest Canada, and Siberia (e.g., Romanovsky
et al.,
2010a
,
2010b
) but with large variability from region to region and for different
parts of the records. In some areas, permafrost is thawing. Permafrost degradation
is of growing concern because of impacts on infrastructure (e.g., roads, runways)
and because thaw may lead to the release of carbon stored in permafrost soils to the
atmosphere (see
Chapter 10
).
Aufeis (German for “ice on top”), a special component of ground ice, represents
layered ice that forms when surface water from springs and groundwater seepage
freezes because of persistent low temperatures, or when rivers overflow their banks,
sometimes as a result of ice jams. It usually melts out during summer and tends
to occur in the same area year after year. Aufeis is also known as “overflow” and
“naled” (a Russian term). Aufeis can be found throughout the Arctic. The total area
of aufeis for all of northern Russia is estimated to be 128,000 km
2
(Kotlyakov,
1997
). The largest single feature in northeastern Siberia (120 km
2
) extends for up to
26 km along the valley of the Momy River (Golubchikov,
1996
). Aufeis accumula-
tion can lead to blocked culverts and flooded roads.
2.2.4
Lakes
Lakes are an important element of the Arctic and subarctic landscape. G. Bonan
(
1995
) estimates that water surfaces (including wet muskeg bogs and swamps)
occupy up to 20-40 percent of the landscape in the glacial drift-covered lowlands
of northern Canada and western Siberia (
Figure 2.16
). In northern Canada there are
several lakes larger than 1,000 km
2
in area. Great Bear Lake (31,000 km
2
) and Great
