Ice Sheets: Lithosphere Cycle A
Laurie Hawkins, Amanda Lynch, Donna Davis, Jessica Wilkinson
The lithosphere contains all the cold, solid land of the planet’s crust or surface.
The lithosphere is very uneven with soaring mountain ranges, flat plains, and
deep canyons. The north and south Polar Regions on the Earth is a unique
geodynamic environment containing the solid crust, salt water oceans, the
cryosphere or frozen water, and the atmosphere. The cryosphere is the term
collectively used to describe the portions of the Earth’s surface where the water
is in a solid form, including sea ice. Sea Ice can range in age from less than a
year old to 10-100,000 years or longer. It is estimated that at some deep ice
locations in East Antarctica the ice could be a million years old.
Cryosphere: Facts, Discussion Forum, and Encyclopedia Article: Sea Ice
http://www.absoluteastronomy.com/topics/Cryosphere
Satellite Imaging Corporation:
http://images.google.com/imgres?imgurl=http://www.satimagingcorp.com/galleryi
mages/greenland_ice_sheets.jpg&imgrefurl=http://www.satimagingcorp.com/svc/
global_warming.html&usg=__ojk6OvxAXuj5lUVQOSRGiDaNMhE=&h=462&w=3
00&sz=137&hl=en&start=1&um=1&tbnid=PTeRhSk_YpLmHM:&tbnh=128&tbnw
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greenland_ice_sheets_page.jpg ¬
Greenland Ice Sheet Melting
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All around us we see evidence of the surface of the Earth changed by the action
of ice sheets and glaciers. Not only do ice sheets act as agents of erosion by
removing huge amounts of rock, soil, and sediment, but they also lay down the
eroded debris in a new location once the ice experiences some melting. This
debris can be deposited under the ice sheet, to the edge of the ice, or beyond the
ice margins. The ice sheets also carve out new landscapes when they move as a
result of melting and gravitational pull. Even though the ice sheets can act as an
agent of erosion, they can also serve as a protector of the underlying ancient
land surfaces that are safe beneath this icy shield. Professor David Sugden of
the University of Edinburgh identified different types of landscapes created by
glacial erosion and deposition. Troughs, hanging valleys, narrow rock peaks,
cirques, high relief mountains, and lakes are just some of the specific land
features that Sugden described.
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With the increase in global warming, the rate of ice sheet melting also increases.
Greenland's ice, for example, is melting at such a high rate that Geophysical
Research Letters predicts that "by 2100 ocean circulation may shift and cause
sea levels off the northeast coast of North America to rise by about 12 to 20
inches more than in other coastal areas." If this happens, many coastal cities
such as New York City and New Orleans could be destroyed by intense flooding.
Although it could be argued that meltwater returns important nutrients to the soil,
it can also pass leave behind pesticides and chemicals that were trapped in the
ice. According to the work of Heidi Geisz and her team of colleagues, an
estimated 2.0-8.8 pounds of DDT are released into coastal waters annually along
the Western Antarctic Ice Sheet from glacial meltwater.
Encyclopedia Britannica
http://www.britannica.com/EBchecked/topic/234619/glacier/65687/Flow-of-theice-sheets
69790-035-C4E0C012.gif ¬
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The images below show the changes in the Arctic sea ice on the Earth from 1981
until 2009. After looking at these images you can observe that the amount of first
year ice, second year ice and older ice decreased from 1981 until 2008. There
seems to be a slight increase in the second year ice in the 2009 image. We need
to remember that the amount of sea ice in 2009 is still below previous years and
remains in a downward trend according to researchers at the University of
Colorado. The cooler conditions on the Arctic Sea surface, possibly the result of
cloudy skies during the late summer, may have slowed the ice loss compared to
the last two years. According to Mike Steele, an Oceanographer from the
University of Washington, the atmospheric patterns in August and September
spread out the ice pack keeping the area cooler.
dlk
Resource: Image http://www.eurekalert.org/pub_releases/2009-10/uocaasi100609.php
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Sea ice covers most of the polar oceans and forms when ocean water freezes.
The sea ice in the Northern Hemisphere experiences less seasonal variation due
to it’s location at a higher latitude and basically being confined to the Arctic
Ocean. The variation in the Northern Hemisphere is only 2, from a minimum of 79 million Km2 in September to a maximum of 14-16 million Km2 in March. The
sea ice in the Southern Hemisphere does vary by a factor of 5 from a minimum of
3-4 million Km2 in February to a maximum of 17-20 million Km2 in September.
(Zwally et al.1983: Gloersen et al. 1992)
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There are several physical properties of snow and ice that influence the energy
exchanges between the surface of the Earth and the atmosphere. The most
important factor that snow and sea ice have on the atmosphere is the reflectance
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(albedo) of radiant heat from the sun back out into the atmosphere. According to
(Hall 1996) the surface roughness is often the dominant factor determining the
strength of radiant backscatter. The Physical properties of snow and ice such as
the crystal structure, density, length, and liquid-water content are important
factors affecting the transfers of heat and water and the scattering of microwave
energy. The darker surfaces of the Earth absorb more light than they reflect
therefore, helping the Earth stay warmer.
Cryosphere: Facts, Discussion Forum, and Encyclopedia Article: Sea Ice
http://www.absoluteastronomy.com/topics/Cryosphere
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The thermal properties of sea ice and snow have important climatic
consequences because the ice and snow absorb heat slower than air. This is
often experienced along coastlines when colder dryer air (land breezes) and
warmer humid air (sea breezes) modify the temperatures. Snow cover insulates
the ground surface and the sea ice insulates the underlying ocean. The
evaporation of surface water is inhibited by even a thin coating of ice. However,
the loss of heat from the water under the sea ice continues until the ice is
between 30 to 40 cm. Snow on top of the ice will slow down the loss of heat from
the water. This insulation of bodies of water with sea ice and snow does impact
the hydrological cycle. The insulating properties of sea ice and snow, also retards
the warming of the water in the spring and summer due to the large amount of
energy needed to melt the ice. This results in a strong static stability of the
atmosphere over areas of large sheets of sea ice and snow. (Cohen and Rind
1991)
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The weight of past and present ice sheets has forced the land in many northern
areas to subside or bend. This happens because under the rigid outer 100 Km of
the Earth (lithosphere), there is a layer called the asthenosphere which is higher
in temperature and is more plastic in nature. As ice sheets covered parts of the
lithosphere the more flexible asthenosphere shifts slightly to accommodate the
ice’s additional weight. After the ice melts the material shifts back up or
rebounds. The rebound is much slower than the melting of the glacier ice sheets.
An example of this is along the Scandinavian coastline. Instead of the sea level
decreasing the land was slowing rising due to adjustment from the reduced load
after the ice sheets melted. If this change in pressure on the land occurs in an
area where there is a fault or crack in the Earth’s lithosphere I wonder if it could
trigger an earthquake in that region.
Scandinavian Coastline and Werner and Neptunism
http://jesse.usra.edu/articles/iceagemodule/resources/html/crustanswer.html
The ANTEC group has developed a vision for a major interdisciplinary study to
investigate the tectonic processes in Antarctica. The study will focus on
understanding 1.) how changing ice mass loads influence lithospheric stress and
strain. 2.) How changing glacial adjustment and tectonothermal structure of the
lithosphere control modern ice sheet behavior. 3.) The history of inception and
growth of Antarctic ice sheets and how these fluctuations are linked to tectonic
activity in the lithosphere. 4.) How do the fluctuations in ice melt/accumulation
change the paleogeography, volcanism, erosion/sedimentation, and climate
changes on the continents? (Wilson, T.J.; Antec Group 2003)
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When you freeze pure water you get a solid block of ice. However, when you
freeze sea water it is different because it is full of dissolved salt. When this sea
water gets cold enough it forms a semi-solid block of ice that is full of little
channels of very salty water called brine. For example: the salt water you would
swim in at the beach usually has 35 ppt (parts per million) of dissolved salt. The
brine found in sea ice channels can be up to 150 ppt. This difference in water
density also contributes to the circulation of water in the ocean. There are lots of
different types of organisms that like to live in these brine water channels. Things
like bacteria, algae, copepods and tiny worms have been found in these unique
environments. These tough organisms that survive under very harsh conditions
are referred to as “sympagic” organisms. For example: the underside of Antarctic
sea ice is the location for sea ice algae to grow and is also a known habitat for
krill. Krill are little crustaceans that form an important link in the food chain of the
Southern Ocean. There is a close relationship between the extent of winter sea
ice and the numbers of Antarctic krill in certain areas. The theory suggested for
this relationship by Dr. Klaus Meiners, Dr. Andreas Krell, Dr. Kerry Swaddling, Dr
Christine Crawford, and Annette Scheltz is that the krill (particularly baby krill) eat
the algae that grows on the bottom of the sea ice.
Sea Ice Ecology
http://www.acecre.sipex.aq/access/page/?page=d664DA82-B244-102A-8EA70019B9EA7C60
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Sea ice has a wide and important role in arctic ecology. Many fish, bird, and
mammal species live on and around sea ice. This sea ice provides shelters for
the underlying water column and blocks sunlight, affecting the ability of the
plankton and algae living in the shallow underside of the ice to live. Moving ice in
shallow water can gouge the seabed which disrupts the benthic communities
allowing additional nutrients and sediments to be absorbed by the water column.
Sea Ice: Implications of changes in arctic sea ice
http:// www.arcus.org/HARC/pdfs/HARC_seaice_report.pdf
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For example studies from ice camps and ships have noted radical changes in
species that live on and near ice packs. Harp seal pups in the White Sea suffered
catastrophic mortality in 1996 and 2001 because the wind changed the location
of ice packs affecting the ability of the food supplies for the pups. Arctic foxes
have been stranded on the shorelines where they need to compete with
terrestrial predators for food.
Sea Ice: Implications of changes in arctic sea ice
http:// www.arcus.org/HARC/pdfs/HARC_seaice_report.pdf
In general we are beginning to understand that sea ice in the Arctic does
profoundly influence arctic ecosystems, the global climate of the Earth, and the
circulation of the oceans and atmosphere in the northern hemisphere. The study
of sea ice is by nature a complicated interdisciplinary undertaking due to the
physical, biological, and human systems that survive in the arctic. The Oscillation
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and other cyclical factors are unclear in the Arctic. The extent to which observed
changes in ice thickness are due to overall thinning versus shifts in the
distribution of the ice in the Arctic Basin needs to be studied further. The
monitoring of the changes in the sea ice requires large-scale remote sensing
systems along with the knowledge of the local people. We need to distinguish
between the role of normal oscillations versus trends in sea ice changes in order
to determine what the long-term impacts will be.
Resources:
Arctic sea ice recovers slightly in 2009, remains on downward trend, and says U.
of Colorado report.
http://www.eurekalert.org/pub_releases/2009-10/uoca-asi100609.php
Wilson, T.J.; Antec Group. American Geophysical Union, Fall meeting 2003,
abstract #C41C-0995 Article: Polar Regions: Natural Laboratories for
Understanding the Dynamic Lithosphere-Cryosphere-Climate System
http://absabs.harvard.edu/abs/2003AGUFM.C41C0995W
Cryosphere: Facts, Discussion Forum, and Encyclopedia Article: Sea Ice
http://www.absoluteastronomy.com/topics/Cryosphere
Scandinavian Coastline and Werner and Neptunism
http://jesse.usra.edu/articles/iceagemodule/resources/html/crustanswer.html
Sea Ice: Implications of changes in arctic sea ice
http:// www.arcus.org/HARC/pdfs/HARC_seaice_report.pdf
Sea Ice Ecology
http://www.acecre.sipex.aq/access/page/?page=d664DA82-B244-102A-8EA70019B9EA7C60
Science Daily
http://www.sciencedaily.com/releases/2007/12/071212103004.htm
http://www.sciencedaily.com/releases/2009/05/090527121055.htm
http://www.sciencedaily.com/releases/2008/05/080526153152.htm
Encyclopedia.com
http://www.encyclopedia.com/doc/1O112-icesheetsandlandscapevltn.html
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