Environmental Engineering Reference
In-Depth Information
rapidly into the ocean. The Smith Glacier, also in West Antarctica, is
moving 83 percent faster than in 1992.
WAIS rests on the sea fl oor; its base is below the ocean surface. Unlike
the primarily land-based EAIS, the bottom of WAIS rests below sea level,
and therefore ocean water is always in contact with the edges of WAIS.
Studies of the responses of marine-based ice sheets to past climate fl uc-
tuations suggest that they can melt and retreat quickly when ocean
temperatures rise because of increased melting at the ocean-ice interface.
In addition, the ocean water may begin to work its way underneath the
base of the ice, which can accelerate melting and lead to greater instabil-
ity, raising the ice sheet so it can cause an extremely rapid rise in ocean
level. Total melting of WAIS would raise sea level 3 to 5 feet.
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Another unevaluated factor concerning the stability of the Antarctic
ice mass is the presence of at least 150 lakes at the base of the ice,
thousands of feet below the ice surface.
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Most of them are beneath
the EAIS. Antarctic glaciologists suspect there may be thousands more.
The meltwater is produced by geothermal heat and collects in hollows
on the rock surface, and there appear to be connections between some
of the lakes—rivers beneath the ice. If there are enough of these sub-
glacial lakes in Antarctica, they would add signifi cantly to the instability
of the ice sheet.
Sea Level Fall
Some coastal areas are experiencing decreases in sea level, despite the
thermal expansion of ocean water and the continuing melting of glacial
ice. Ocean levels are indeed rising in these areas, but the land is rising
even faster so that the shoreline is receding. The areas of rising land
are in Northern Hemisphere areas formerly covered by billions of tons
of glacial ice a few tens of thousands of years ago—Alaska, much of
Canada, Greenland, Scandinavia, and Siberia. The land is rising in
response to removal of the ice during the interglacial period that began
20,000 years ago. Land is rising from the water, shifting property
boundaries and creating land whose ownership is unclear.
In some areas around Juneau, Alaska, the land is rising almost 3
inches a year.
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Relative to the sea, land around Juneau has risen as much
as 10 feet in about 200 years. As global warming accelerates and more
ice melts, the land will continue to rise—perhaps 3 feet more by 2100,
scientists say. Adding to the glacial rebound is movement of the Pacifi c
plate as it slides beneath the North American plate.
