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From: Marilou Hawkins
Date: 10/30/02
Time: 10:16:11 PM
Remote Name: 207.65.228.7
What is Sea Ice? Sea ice is any form of ice found at sea which originated from freezing of seawater. An ice shelf is the floating extension of the grounded ice sheet. It is composed of freshwater ice that originally fell as snow. Sea ice can be broadly described as new ice, young ice, first-year ice, and old ice. New ice is a general term for ice recently formed, includes franil ice, grease ice, slush, and shuga. All of these would be less than 10 cm thick. Nilas, another new ice, is a thin elastic crust of ice, easily bending on waves and swells under pressure, thrusting in a pattern of interlocking “fingers” pressure process whereby one piece of ice overrides another. It has a matt surface and is up to 10 cm in thickness. Young ice is in the transition stage between Nilas and first-year ice, 10-30 cm in thickness. First year ice is sea ice of not more than one winter’s growth. It develops from young ice. Its thickness is around 30 cm- 2cm. It may be subdivided into thin first-year ice/white ice, medium first-year ice is 70-120 cm think and thick first year-ice is over 120 cm thick. Old ice has survived only one summer’s melt. Because it is thicker and less dense than first- year ice, it stands higher out of the water. It is the most common form of ice on the Antarctica. http://www.antcrc.utas.edu.au/aspect/seaiceglossary.html http://bsxisgb.nbs.ac.uk http://whyfiles.org/091beach/5.html What is the atmosphere? The Atmosphere is the gaseous/vaporous envelope surrounding the earth. It consists of several layers: troposphere, stratosphere, mesosphere, and thermosphere with the troposphere at the surface of the earth, and the thermosphere spreading out into space. The portion of the atmosphere we experience day to day is the troposphere; its movements produce weather. The stratosphere contains the ozone layer that protects Earth’s surface from many UV rays. The planet is a natural greenhouse. Some naturally occurring greenhouse gasses permit incoming solar radiation to reach Earth’s surface, but restrict the outward flow of infrared radiation. Carbon dioxide and water vapor absorb this outgoing infrared energy and re-radiate some of it back to ground level. This greenhouse effect is essential to most life on Earth. Without it the average temperature would be a frigid –18Cº, rather than the 14Cº as it is today. The concentration of greenhouse gases in the atmosphere, especially carbon dioxide, has been increased by the human combustion of fossil fuels, exacerbated by deforestation. Humans have added other greenhouse gases such as methane, CFCs, and nitrous oxide to the atmosphere. The combined effect of these additional gases will be a rise in global temperatures, predicted by climate models to be between 1Cº and 4Cº by the end of this century. Global warming is not expected to be uniform over the globe because of the complex interactions within and between the lithosphere, hydrosphere and atmosphere. Some of the most profound changes are expected at the higher latitudes. Exposed ocean and bare earth, caused by the loss of ice and snow from melting, will result in increased absorption of solar energy (a positive feedback). Conversely, this situation will increase heat fluxes from the ocean to the atmosphere caused by the decrease in sea ice (a negative feedback) This requires us to study the Antarctic climate processes contributing to the climate system, and determine the response of the Antarctic to past climate change and compare past and present changes to estimate how many of the changes have anthropogenic causes. Many important Antarctic processes involve ice, snow and sea ice. Ice and snow, snow particularly, with its albedo limits absorption of solar energy, and sea ice acts as a blanket preventing latent heat transfer between the ocean and atmosphere. (http://www.antidiv.gov.au/magazine/autumn02/html/03_Antarctic_i) http://encarta.msn.com/encnet/refpages/refarticle.aspx?refid=761559991 A>E: Intense global warming of more than 0.5 degrees Celsius per decade over the last thirty years has lead to the decline of sea ice. Computer generated models suggest that if greenhouse gases continue to warm the Earth, permanent ice packs will likely melt and will be replaced with seasonal winter ice. (http://archive.greenpeace.org/~climate/arctic99/reports/seaice3.html) A>E: Major changes in the Arctic air circulation patterns have also affected sea ice. Over the central Arctic Ocean, average sea level pressure has dropped, and high latitude storms have increased. This has resulted in considerably warm spring and summer air masses over the Arctic Ocean area, which melts some sea ice and pushes the remaining ice away from the shore. (http://archive.greenpeace.org/~climate/arctic99/reports/seaice3.html) A>E: A lengthening warm season is also contributing to sea ice decline. When there are open areas of water, called “leads“, darker areas of the ocean reflect less sunlight, therefore, warm up and melt even more ice. (http://archive.greenpeace.org/~climate/arctic99/reports/seaice3.html) E>A: In 1994, the British Antarctic Survey (BAS) released data demonstrating that the average temperature on the Antarctic Peninsula had warmed by 4.5 degrees Fahrenheit since 1947. The building of sea ice (event) increases the reflection of more solar radiation than bare land surface back into stratosphere and mesosphere (atmosphere) because water and earth being darker than ice, absorb more sunlight and warm the whole planet. As the sea ice doubles in size, the reflection rate increases causing a rise in temperature of our atmosphere and more global warming. Researchers at the University of Colorado at Boulder recently discovered that air temperature in Antarctic rose 18 degrees Fahrenheit in just a few decades. The largest warming ever recorded in the Southern Hemisphere. That temperature change is only now making its way to the bottom of the two-mile thick icecap, where it may be affecting how the ice flows. The region has now entered a vicious cycle of polar warming: rising average temperatures, fewer cold years and longer summer melting have resulted in the warming of Antarctica’s waters. This has resulted in a decrease in sea-ice extent. With a loss of sea ice and ice shelves, reduced albedo (reflective power) causes a change in the absorption heat and carbon dioxide, which means more warming. This has caused two ice shelves to break up and melt faster than anyone expected. A warming trend in the region has caused the annual melt season to increase by two or three weeks over the last 20 years. The Larsen B and Wilkens ice sheets on the Antarctic Peninsula have lost nearly 3,000 sq. km of their total area in 1998. Scientists expected the two shelves to fail soon, but the current disintegration is occurring at an even faster rate than earlier breakups because of the warming trend. Scientists believed the Larsen B ice shelf has existed for a t least 400 years. It is roughly the size of Connecticut. The local climate is inching toward an average summertime temperature just above 32 degrees Fahrenheit-melting point of water. http://www.enn.com/enn-news-archive/1999/04/040999/iceretreat_z583.asp http://www.asoc.org/general/iceshelve.htm . Meltdown: Satellites Show Accelerated Polar Ice Threat by Robert Roy Britt Sunday Report: Melting Releases Riddles on Global Warming Los Angeles Times, 04/01/01 E>A: The loss of the Lassen ice shelf means reduced area of reflective surface and subsequent increase of absorption of solar radiation. It also means a greater transfer of latent heat form the ocean to the atmosphere and from the atmosphere to the ocean because of the loss of sea ice to act as a thermal blanket. (http://www.ncdc.noaa.gov/pw/cg/cryo_doc.html) E>A: Sea ice helps modify the transfer of heat, mass, and momentum between the atmosphere and the ocean. It acts a physical barrier to the exchange of gases, such as carbon dioxide, oxygen and water vapor. Sea ice behaves as an insulating cover between the cold atmosphere and the considerably warmer ocean. During the winter, the loss of heat to the atmosphere over sea ice is “two orders of magnitude smaller” than loss of heat over open ocean. Sea ice also reflects solar radiation back to space rather than allowing the ocean surface to absorb it. (http://www.antcrc.utas.edu.au/aspect/seaiceintro.html) E>A: Removal of permanent ice packs would significantly increase precipitation in the Arctic Ocean and North Atlantic. Such precipitation, combined with melted sea ice, would result in the reduction of salinity of the ocean water. The North Atlantic Conveyor, which is the main driving force for the Gulf Stream and global ocean circulation, could be severely reduced by these changes in salinity. Furthermore, northern Europe’s climate would be cooled, global marine life would be disrupted, and the ocean would have a reduced ability to remove greenhouse gases from the atmosphere. (http://archive.greenpeace.org/~climate/arctic99/reports/seaice3.html) However, the last time the North Atlantic Conveyor was halted was when the North American ice sheet retreated to the St. Lawrence Valley and released enormous quantities of fresh water into the North Atlantic. This was coincidental to if not the cause of the Younger Dryas cold event 13,000-11,500 years ago. (Raymond S. Bradley, Paleoclimatology: Restructuring Climates of the Quartenary, 2nd Ed. Pp. 271-279) Resources: http://www.antcrc.utas.edu.au/aspect/seaiceglossary.html http://bsxisgb.nbs.ac.uk http://whyfiles.org/091beach/5.html http://encarta.msn.com/encnet/refpages/refarticle.aspx?refid=761559991 http://archive.greenpeace.org/~climate/arctic99/reports/seaice3.htm http://www.enn.com/enn-news-archive/1999/04/040999/iceretreat_z583.asp http://www.asoc.org/general/iceshelve.htm . Meltdown: Satellites Show Accelerated Polar Ice Threat by Robert Roy Britt Sunday Report: Melting Releases Riddles on Global Warming Los Angeles Times, 04/01/01 http://www.antidiv.gov.au/magazine/autumn02/html/03_Antarcti http://www.ncdc.noaa.gov/pw/cg/cryo_doc.html http://www.nsf.gov/pubs/1999/nsf98016htm/nsf98106m6.html http://www.space.com/php/multimedia/imagdisplay/img_display http://www.space.com/scienceastronomy/antarctic_020822.htmll