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
Satellite Imaging Corporation:
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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
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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 ArcticSea 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.
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Resource: Image
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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 7-9 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 (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
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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
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
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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
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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
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 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 ArcticBasin 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 saysU. of Colorado report.
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
Cryosphere: Facts, Discussion Forum, and Encyclopedia Article: Sea Ice
Scandinavian Coastline and Werner and Neptunism
Sea Ice: Implications of changes in arctic sea ice
Sea Ice Ecology
Science Daily
Encyclopedia.com
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