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Biosphere and Ice Shelf Issues

From: Cat
Date: 10/29/02
Time: 2:39:02 AM
Remote Name: 80.74.170.117

Comments

Here's what we have on background. I'll add some chains tomorrow. Cat

Ice Shelf Disintegration and the Biosphere:

The biosphere, a termed coined by Russian scientist Vladimir Vernadsky in 1929, is the life zone of the Earth and includes all living organisms, including man, and all organic matter that has not yet decomposed. Life began on earth millions of years ago and the biosphere readily distinguishes our planet from all others in the solar system. The biosphere is structured into a hierarchy known as the food chain whereby all life is dependent upon the first tier (i.e. mainly the primary producers that are capable of photosynthesis). Energy and mass is transferred from one level of the food chain to the next with an efficiency of about 10%. At each level, the consumer gets only about 10% of the stored energy of what it consumes. All organisms are intrinsically linked to their physical environment and the relationship between an organism and its environment is the study of ecology. The biosphere can be divided into distinct ecosystems that represent the interactions between a group of organisms forming a trophic pyramid and the environment or habitat in which they live. (http://www.geology.ufl.edu/Biosphere.html) The biosphere is the one place where all the four spheres of the planet work together. The land (lithosphere) interacts with the water (hydrosphere) and it also interacts with the air (atmosphere). Each of these interactions will interact with the biosphere at all times. All of the interactions are affected by the energy that surrounds us. All of those forces work together to create our living world. (http://www.geoghraphy4kids.com/files/land_biosphere.html)

Ice shelves formed from glaciers and ice sheets flow over the edge of the continent of Antarctica and float in the surrounding ocean. These shelves of thick freshwater ice are extensions of the grounded ice sheet and flow from the land to the sea where parts (icebergs) break off, or are calved. (http://www.meteor.iastate.edu/gcp/sealevel/ross.html) The rate at which an ice shelf flows is dependent on the ice thickness and temperature, and the shape of the surrounding lands which it flows past. (http://web.pdx.edu/~chulbe/science/Larsen/larsen2002.html) Ice shelves gain mass by flow from grounded ice sheets and glaciers and new snow accumulation on their surfaces. They lose mass primarily by iceberg calving and secondarily by melting. Ice shelves balance between gravity-driven horizontal spreading and stresses at the grounding lines and the calving seaward front. The small thin ice shelves that fringe the Antarctic Peninsula are sustained primarily by new snow accumulation; larger ice shelves such as the Ross Ice Shelf are sustained mainly by flow from inland ice sheets. Thickness of these ice shelves is approximately 200m. Changes in winter accumulations or summer melting are of fundamental importance to the health of fringing ice shelves. (http://nsidc.org/iceshelves/larsen1995/index.html)

The Larsen Ice Shelf, located on the Antarctic Peninsula, has recently had a greater increase in temperatures than the rest of the continent, and has been warming five times faster than the global average. (http://www.climatehotmap.org/antarctica.html) The shelf has lost about 2200 square miles of ice over the last five years. However, the Ross Ice Shelf, located closest to New Zealand, has been cooling and gaining mass as it thickens since the glacial streams flowing over it have slowed down. Giant icebergs have calved (broken away) from the Ross Ice Shelf in March 2000, March 2002, and May 2002. (http://www.exploratorium.edu/climate/cryosphere/data5.html)

The disintegration of the Larsen B Ice Shelf in west Antarctica (closest point to South America) sent thousands of small icebergs adrift in the Weddell Sea. This was the largest single loss in a series of recent events leading to the break down of this ice shelf (http://www.exploratorium.edu/climate/cryosphere/data5.html) and followed the warmest summer on record around the Antarctic Peninsula. (http://web.pdx.edu/~chulbe/science/Larsen/larsen2002.html) While iceberg calving is normal for ice shelves, disintegration is not. Farther south, at the same time as the disintegration, a large iceberg broke off the ice shelf seaward front. (http://nsidc.org/iceshelves/larsen1995/index.html) The disintegration break up lasted for 35 days from January through late March 2002. Scientists attribute the collapse to its warming by 2.5 degrees Celsius (4.5 degrees Fahrenheit) since 1945. Other breakup events of the Larsen Ice Shelf include the disintegration of the Larsen A section in 1995 reducing the shelf by 770 square miles, and the collapse of the Larsen B and Wilkins Ice Shelves between March 1998 and March 1999 reducing the shelves by 1150 square miles. (http://www.climatehotmap.org/antarctica.html; http://earthobservatory.nasa.gov/Study/LarsenIceShelf/)

Researchers propose that the ice shelf disintegration is caused by increased melt water ponds on the ice shelf surface due to the extended melt seasons in summer, as the temperatures increased. Water from these ponds fills in the crevasses in the ice surface causing them to continue through the ice shelf thickness due to the added weight of the water in the crack. With these fractures in place, the ice shelf is vulnerable to rapid break up from winds, tides, or another melt season. Satellite imagery has supported this theory as ponds were seen to contract, indicating water was draining to the sea, prior to the last disintegration event. (http://web.pdx.edy/~chulbe/science/Larsen/larsen20002.html; http://nsidc.org/sotc/iceshelves.html) Thus the mean summer temperature may be more indicative of ice shelf destruction than the previously thought mean annual temperature. Summer temperatures above freezing are more likely to promote ice shelf retreat. (http://earthobservatory.nasa.gov/Newsroom/NasaNews/20010200102264406.html)

Disintegration of the ice shelf does not contribute to an increase in sea levels since the ice shelf is already floating prior to the collapse. However, ice shelves do serve as natural barriers to the flow of ice from glaciers. Thus, continued disintegration could lead to a rise in sea levels if glaciers were able to dump ice into the ocean more quickly, (http://yosemite.epa.gov/oar/globalwarming.nsf/content/NewsandEventsScienceandPolicyNews.html; http://nsidc.org/iceshelves/larsen1995/index.html) perhaps as much as by 19 feet (five meters). (http://www.climatehotmap.org/antarctica.html; http://earthobservatory.nasa.gov/Newsroom/MediaAlerts/2002/200203188307.html)

Sea ice is water in a frozen state floating on the ocean’s surface. It helps regulate the water’s temperature, salinity, and currents. The extent of sea ice is seasonal and responds quickly to changes in air temperatures. The extent of sea ice can now be monitored daily thanks to microwave sensors on satellites. (http://www.exploratorium.edu/climate/cryosphere/data4.html) Sea ice is the thin, fragile, solid layer of ice that forms in the North (Arctic) and South (Antarctic) Polar regions. It forms a boundary between the relatively warm ocean and the cooler atmosphere. There are many different kinds of sea ice: first year ice, ridges, and multi-year ice. Sea ice will float because it is less dense in the solid phase than it is in the liquid phase. If sea ice were denser in the solid phase, it would cause it to sink to the bottom of the ocean causing the oceans to freeze to their beds. This would cause the animals and plants which live on the ocean floor to die. (http://southport.jpl.nasa.gov/polar/iceinfo.html) Sea ice is also an interesting habitat for a variety of organisms; often inaccessible to further on site study. Penguins, whales and phytoplankton all can live on sea ice. (http://www.awi-bremerhaven.de/Eistour/index-e.html)

Snow and ice reflect great amounts of solar energy back into space. This helps keep the earth cool. Reduction in the amount of snow and ice cover would allow for more solar energy to be absorbed which could lead to increased global warming. (http://www.exploratorium.edu/climate/cryosphere/index.html)

For the purpose of this sphere study we will focus on ice shelf disintegration and its effects on the biosphere.

E>B

Giant icebergs calved from ice shelves can cause a risk to navigation (and thus people) as they drift into open water. (http://www.cnn.com/2002/TECH/space/05/09/iceberg.satellite/index.html)

E>B

The growth of phytoplankton in the southwestern part of the Ross Sea had been reduced by the large icebergs that calved from the Ross Ice Shelf in 2000. Data from satellites showed a decrease in volume of these tiny plants by about 40% between March of that year and December 2001. After breaking away, the icebergs grounded on the sea floor about 100 kilometers from the ice shelf blocking the path of sea ice from flowing out to the open seas. Plankton requires the open water and direct sunlight to survive. (http://www.newscientist.com/hottopics/climate/climate.jsp?id=ns99992203) Phytoplankton, rich in chlorophyll, is the base of the local food chain for marine mammals and birds. Less plankton could lead to reduced numbers of these organisms.

E>B

The fresh water from the melted ice stays at the top of the salt water where diatoms (a silicate covered phytoplankton) flourish. The Ross Sea is an example of where this occurs. Another species of phytoplankton, Phaeocystis antarctica, is a nearly twice as productive carbon dioxide using organism – thereby very beneficial to us. “Should the phytoplankton community shift from P. Antarctica to diatom dominance in response to enhanced upper ocean stratification, the capacity of the biological community to draw down atmospheric carbon dioxide could diminish dramatically.” Increased levels of carbon dioxide could be devastating to the biosphere. (Arrigo in http://earthobservatory.nasa.gov/Study/Polynyas/)

E>B

Krill is a tiny shrimp-like crustacean. They feed on sea ice algae or phytoplankton, and juveniles especially seek protection from predators in the cracks of the ice. They provide the staple diet for many fish, birds, and mammals in the Southern Ocean. (http://www.awi-bremerhaven.de/Eistour/index-e.html) Loss of sea ice would mean less krill and could have a disastrous effect on the regional food chain.

E>B

Adelie penguins are found on the sea ice surrounding Antarctica where sea ice lasts throughout the winter and well into the spring thaw. During winter, the penguins dive to catch krill in the cracks in the ice. When the sea ice is reduced, suitable feeding sites become scarce or too far away for the birds, thus reducing their survival. If the sea ice is diminished, there would be less Adelie penguins. Due to the warmer temperatures on the Antarctic Peninsula, the colonies of the Adelie penguins have diminished and are being replaced by colonies of other penguin species such as the gentoos and chinstraps which are not so dependent on the sea ice. (http://www.bbc.co.uk/nature/earth/warnings/antarctic_all.shtml) The annual melt season has increased by 2 to 3 weeks in just the last twenty years. The Adelie penguin populations have shrunk by 33% over the past 25 years due to the loss of their winter sea ice habitat. (http://www.climatehotmap.org/antarctica.html)

E>B

Scientists have proposed that the amount of krill, tiny crustaceans, relates to the amount of sea ice. Sea ice offers protection to the krill and provides them with a food source in the form of ice algae which grows in small cracks on the underside of the sea ice. Krill and Salpa thompsoni, or salps, are competitors. Large numbers of salps inhibit krill reproduction. Warmer temperatures favor larger numbers of salps and less numbers of krill, while colder temperatures and more sea ice favor krill. Salps prefer open sea environments, thus warmer temperatures and less sea ice. They reproduce asexually in early spring consuming phytoplankton which in turn limits the amount available to krill which inhibits their reproductive development and spawning. Krill reproduce later, and salps are predators of krill larvae. Years of less sea ice have resulted in smaller amounts of krill and larger amounts of salps. However, during years of extensive sea ice coverage, krill seem to spawn early. Krill are an essential part of the diets of whales, penguins, squid, seals, seabirds, and fish, while salps are not. Decreased amounts of krill could have a great effect on the Antarctic food chain. (http://earthobservatory.nasa.gov/Study/UpperCrust/)

E>B

Parts of the Arctic and Antarctica have experienced warming temperatures well above the global average for the past few decades. Reduced sea ice and ice shelves affect native plants and animals which in turn provide food and resources to people. (http://www.climatehotmap.org/antarctica.html)

E>B

Arctic sea ice is a critical part of the ecosystem for Arctic organisms such as polar bears, seals, and walruses that depend on it for their habitat as they rest, forage, mingle, and breed there. Reduced amounts of this sea ice could have an adverse effect on these animals and their survival. (http://earthobservatory.nasan.gov/Study?ClimateClues/; http://nsidc.org/sotc/sea_ice.html)

E>B

Shipping companies moving raw materials such as oil or coal out of the Arctic must work around the sea ice, thus shipping during times of limited sea ice. Less ice would enable them to ship goods for longer periods throughout the year. More ice makes it treacherous to navigate through barely open pathways. (http://nsidc.org/sotc/sea_ice.html)

E>B

At least four seal species (Weddell, Crabeater, Leopard, and Ross seals) use sea ice for resting and hunting, as well as a place to give birth and seek refuge from predators. (http://www.awi-bremerhaven.de/Eistour/index-e.html) Decreased amounts of sea ice could adversely affect these species.

E>B With the disintegration the melting water would lower temperature causing the living things in the water surrounding the melting to be exposed to colder water temperatures and even untimely death due to the extreme cold. (http://www.learnz.org.nz/old/98/seaice2.htm; and http://www.awi-bremerhaven.de/Eistour/pinguine-e.html )

E>B When the breaking away of an iceberg happens and disintegration begins the moving ice can block or close off certain places on the ice shelves. Emperor penguins, which are entirely dependent on the sea ice to breed and rear their young, may be unable to reach their breeding grounds because of this and therefore unable to breed. This will result in a decrease in the Emperor penguin population. (http://www.enn.com/news/en-stories/2002/01/01102002/s_46027.asp; and http://www.awi-bremerhaven.de/Eistour/pinguine-e.html)

E>B Ice Shelf Disintegration could cause trade for food to shut down which would result in less imports of food that the living population needs. Hunger could result. With the disintegration of the ice shelf, the shipping lanes would be pushed further back. Ships could not sail into or on the melting ice shelves. If ships could not reach their destination then trade could not happen which would result in no trade (that trade could be food) and if food could not get through, then hunger and starvation could result. (http://www.learnz.org.nz/old/98/seaice2.htm; and http://www.coolantarctica.com/Antarctica%20fact%20file/antarctic.../seaaice%20formation.ht)

B>E Living things emit lots of energy and chemicals into the environment. One such chemical, carbon dioxide, a greenhouse gas, could play a role in the melting of ice or helping it to disintegrate at a quicker pace due to the emitting of carbon dioxide or other chemicals. (http://www.geology.ufl.edu/Biosphere.html; and http://igbp.kva.se/cgi-bin/php/scienchistory.show.php?section_id=11&article_id=146)

B>E Manmade drilling machines or boat routes, etc. can contribute to the cause of ice shelf disintegration through the use of machinery and boats to get through to certain places that the ice shelves may block. They may be trying to reach trade routes, people, etc. but in trying to make a way in the ice it disturbs the natural balance of things and allows for pieces to be broken from the ice shelf that normally would not be done by nature causing further disintegration to the ice shelf. (http://www.coolantarctica.com/Antarctoca%20fact%20file/antarctic...ht; and http://southport.jpl.nasa.gov/polar/iceinfo.html)

E>B

Ice shelf disintegration would greatly raise the freshwater levels in the ocean while disturbing the salt levels in the ocean. Sea ice, while made of sea water, is surprisingly unsalty. The salt dissolves when the ice is formed, so when the sea ice is formed the melting would put fresh water into the salty ocean water and this would disturb the salt levels in the ocean. With the salt levels disturbed, the ocean sea life could be harmed or even die from the changes in the salt levels. (http://www.learnz.org.nz/old/98/seaice2.htm; and http://www.awi-bremerhaven.de/Eistour/index-e.html)

Ice shelf disintegration greatly affects the biosphere. Continued loss of sea ice can adversely affect the regional and in time the global biosphere as food chains are disrupted and habitats lost. “The total volume of the ice sheet covering Antarctica is estimated to be 29 million cu km (7 million cu mi), or about 90 percent of the world’s ice. If the ice sheet melted, the oceans of the world would rise by 60 m (200 ft). Some 11 percent of the ice sheet consists of ice shelves—massive floating slabs of permanent ice fringing the continent—that are anchored to the rock and extend into the surrounding ocean. The largest, Ross Ice Shelf, is about the size of France. The Antarctic ice sheet has an average thickness of 2,160 m (7,090 ft); its greatest recorded depth is more than 4,700 m (15,400 ft).” (Microsoft® Encarta® Reference Library 2002. © 1993-2001 Microsoft Corporation.)

Resources:

(http://earthobservatory.nasa.gov/Newsroom/MediaAlerts/2002/200203188307.html)

(http://earthobservatory.nasa.gov/Newsroom/NasaNews/20010200102264406.html)

(http://earthobservatory.nasan.gov/Study?ClimateClues/ )

(http://earthobservatory.nasa.gov/Study/LarsenIceShelf/ )

(http://earthobservatory.nasa.gov/Study/Polynyas/)

(http://earthobservatory.nasa.gov/Study/UpperCrust/) (http://igbp.kva.se/cgi-bin/php/scienchistory.show.php?section_id=11&article_id=146)

(http://nsidc.org/iceshelves/larsen1995/index.html)

(http://nsidc.org/sotc/sea_ice.html )

(http://southport.jpl.nasa.gov/polar/iceinfo.html)

(http://web.pdx.edu/~chulbe/science/Larsen/larsen2002.html)

(http://yosemite.epa.gov/oar/globalwarming.nsf/content/NewsandEventsScienceandPolicyNews.html)