2001 EARTH SCIENCE VIDEOTAPES |
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Tape Title | Record ID | Date Produced | TRT: |
Synopsis |
| CRACKS IN THE ICE: NEW INSIGHTS INTO ANTARCTIC ICE SHELF FAILURES | G01-003 | 1/09/01 | 00:12:30 | Most people regard the desolate expanses of polar ice as practically unchanging and imperturbable, poetically bookending the rest of our vibrant, blue-green world. Not so, says a new study. According to a paper released in the latest issue of the Journal of Glaciology, major stretches of Antarctica's Larsen Ice Shelf literally collapsed into floating splinters as several recent warmer than normal summers took their toll. The research adds strong evidence to the case that climate change can have a significant impact on the condition of the Earth's polar caps, which in turn can play a major role in changes to wider planetary climate and environmental conditions.
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TAPE CONTENTS: |
| ITEM (1): The Big Breakup (VO) - First there was this (still before):
Then this: (still after)
Your looking at a dramatic process of change in a part of the world generally difficult to study: Antarctica. (Radarsat Antarctica tilt up) Here's what happened: warmer than normal summertime temperatures there enabled melt water to pool on the surface of the Larsen Ice Shelf. Those pools then drained into cracks, acting as powerful hydraulic wedges. Experts say it's this process which weakened the shelf, and ultimately caused an area about the size of Rhode Island to break off between 1995 and 1998. For now, beach property in the rest of the world is safe. The Larson Ice Shelf was already mostly floating, and thus ocean levels hardly changed after the breakup. But scientists say these findings should encourage a close eye on conditions that could provoke similar failures elsewhere. If the much larger Ross Ice Shelf were to collapse, it's possible that global ocean levels might perceptibly rise as Antarctic glacial ice escaped from the continent's interior into the sea.
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| ITEM (2): Zooming in For a Closer Look - In 1995 alone, a region of ice on the Larsen Ice Shelf more than two-thirds the size of Rhode Island disintegrated in a fierce storm. Additional area broke away from the rest of the shelf in 1998. This dramatic change to so much ice is the product of several forces acting in concert. In this visualization we start from above and zoom in to the specific area of study.
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| ITEM (3): Surface Water - This image shows a section of the remaining Larsen Ice Shelf. The dark patches scattered around the white background are regions of surface melt water, formed during the summer season. It's from these pools that water drained into cracks in the shelf to form the wedges that ultimately shattered the ice. NASA's Landsat 7 spacecraft took this picture on August 9, 2000.
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| ITEM (4): Before And After - The Larsen Ice Shelf is one of several so-called ice shelves in Antarctica. Although not the largest, experts consider it to be most in jeopardy of further recession due to its comparatively northern position. In this sequence, we see how the ice there has changed through time, starting in December 1993 and ending in March 2000. These images are the product of NOAA's AVHRR instrument, (Advanced Very High Resolution Radiometer), flying aboard that agency's POES (Polar Orbiting Environmental Spacecraft) satellite.
Image dates are the following:
December 26, 1993
February 13, 1995
March 21, 1998
November 21, 1998
March 2, 2000
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| ITEM (5): A Process of Change: What Happened to Shatter The Ice - As melting water on the surface of an ice shelf fills in fissures and crevasses, pressure builds in the structure of the sheet. That process can either increase gradually, or it can be repeated seasonally, with melting and re-freezing forcing the split to widen. What can happen is either a major break due to specific forces from the water wedge, or a gradual weakening of a wide section of shelf, ultimately rent asunder by tides or storms. The process is believed to be more a function of mean summertime temperatures, as opposed to overall annual temperatures.
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| ITEM (6): A Look at The Retreating Ice Sheet - We start this animation with a look at Antarctica's ice pack as it appears today. Then the scene changes to describe how the continent likely looked at the peak of the last ice age, nearly 20,000 years ago. As the years roll backwards, we see just how significantly the area can be altered as planetary conditions change. Consider that since the last ice age, the west Antarctic ice sheet has lost nearly two thirds of its mass during this period, a volume of ice sufficient to raise sea levels approximately 33 feet around the globe.
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| ITEM (7):
A Tour of Several Antarctic Ice Sheets
Larsen Ice Shelf - In 1978, scientists predicted that global warming would lead to a disintegration of Antarctic Peninsula ice shelves. Spaceborne data indicate that this prediction may be coming true. In these before and after images, note the dramatic change in the apparent shoreline. Scientists captured the first image in using the ERS-1 satellite in 1992. In the second image, collected by Radarsat in 1997, huge changes have come to the coastline.
Fimbul Ice Shelf - Icebergs form when hunks of ice break away from glaciers pushing into the ocean. Ice shelves are the edges of those glaciers, extending out into the ocean faster than ice bergs can break off from the edge. The Fimbul Ice Shelf has remained relatively consistent in its appearance for the last thirty years, but researchers are paying close attention to changes. Ice shelves are considered to be particularly sensitive to climatic changes and scientists have detected a marked retreat of several along the Antarctic Peninsula.
Amery Ice Shelf - At the mouth of the Lambert Glacier spreads the Amery Ice Shelf. For the most part, ice shelves grow from glaciers pushing down into the sea. To a lesser extent they also grow from precipitation. Ice Shelves respond to climate change faster than sheets of ice on the ground or continental glaciers. Of particular interest is whether observed changes in various ice shelves are the result of natural processes or are anthropogenic, that is, the result of actions taken by humans.
Ronne Ice Shelf - The Ronne Ice Shelf grows primarily due to a constant flow from inland ice sheets. Where shearing stresses are greater than the strength of the ice itself, cracks form. These cracks ultimately widen and spread like varicose veins in the frozen skin of the coast, only to break loose and become icebergs. Early in the 1990's a slab of ice the size of Delaware broke free from this area. A recent iceberg more than 40 miles wide now floating in the South Atlantic originated from the Ronne Ice Shelf.
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| ITEM (8): LANDSAT 7- Keeping an Eye on The Earth's Changing Face - From an altitude of 438 miles (730 kilometers), Landsat 7 can see surface features as small as 15 meters, providing world-wide land resource information for a diverse range of uses. The satellite is part of a global research effort NASA calls the Earth Science Enterprise, which seeks to acquire a long term understanding of the changes to our planet. Landsat 7 is the latest in a series of satellites. Since the program started in 1972, it has paved the way in research and data acquisition techniques about the surface of our planet.
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| ITEM (9): The RADARSAT Satellite - NASA launched the Radarsat satellite for the Canadian Space Agency in exchange for certain operational executions. Unlike mapping satellites that rely on reflected sunlight or infrared readings, Radarsat's Synthetic Aperture Radar (SAR) is able to penetrate cloud cover or work in the dark of night. Courtesy: Canadian Space Agency/GSFC Studio 13
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Earth Science Gallery