August 18, 1999
The West Antarctic Ice Sheet
1. The West Antarctic Ice Sheet and Ross Ice Shelf draining into the Ross Sea. The background image is a mosaic of Advanced Very High Resolution Radiometer (AVHRR) imagery.
2. Antarctica, showing the location of figure 1 (box).
Click on images for larger views and additional information.
Image Credit: R. Whritner, Scripps Institution of Oceanography.
There are indications that, due to the current climatic warming trend, the West Antarctic Ice Sheet is not stable and may melt in the course of the next several hundred to few thousand years.
If this were to happen, the consequences would be dramatic: The global sea level would rise by about 16 to 20 ft (5 to 6 meters) and affect coastal areas around the world, disrupt global oceanic circulation patterns, and trigger further climate change.
Why do some scientists think that the West Antarctic Ice Sheet might melt?
The West Antarctic Ice Sheet
In contrast to the ice sheet of East Antarctica, which resides mainly on land and above sea level, that of West Antarctica extends in several regions from land outward into the sea. It is a "marine" ice sheet. Large portions of its ice rest on the ocean floor well below sea level. Beyond, the ice extends as floating ice shelves for miles out into the sea. The three largest examples of marine ice shelves in West Antarctica are the Ross, Filchner, and Ronne Ice Shelves (see enlarged view of image 2).
Close to the shorelines of the West Antarctic Ice Sheet, ice streams, lubricated by subglacial water and slippery marine deposits, flow down the slopes toward the ice shelves at speeds roughly 10 to 100 times the speed of the bulk of the ice sheet. Figure 1 illustrates six of the ice streams flowing toward the Ross Ice Shelf (marked A-F). These ice streams contribute significantly to the rate at which ice from the interior gets discharged into the sea.
Potential Instability of the West Antarctic Ice Sheet
If the current climatic warming trend continues, the parts of the West Antarctic Ice Sheet that rest on the ocean floor may start to melt and thin. Once this happens, the ice will rise off the ocean floor due to reduced weight. This, in turn, will allow ocean water to get underneath and accelerate the melting at an ever-increasing rate, possibly bringing about the "collapse" and disappearance of the ice sheet.
Adding still further to the ice sheet collapse are the ice streams, whose flows are likely to increase as their slopes steepen due to the retreat of the ice sheet from the sea toward the shoreline.
In contrast, the ice sheet of East Antarctica, which, with minor exceptions, does not extend out into the sea, is believed to be stable.
Past Examples of Marine Ice Sheet Collapse
During the last glacial period, which reached its peak about 20,000 years ago, large marine ice sheets existed in both the Northern and Southern Hemispheres. Due to the gradual warming that followed, they all disappeared by about 6,000 years ago, except for the West Antarctic Ice Sheet and some minor marine ice sheets of East Antarctica (e.g., that of the Lambert Glacier).
Scientists are not sure whether the West Antarctic Ice Sheet will indeed disappear. However, they take this possibility seriously. By carefully monitoring the changes in its thickness via satellite observations, in situ measurements, and numerical modeling, they expect to soon have a better understanding of what the future might hold.
More Cool Stuff
- We obtained image 1 above from the West Antarctic Ice Sheet (WAIS) Initiative Web site:
- http://igloo.gsfc.nasa.gov/wais/
- For an extensive summary of Arctic and Antarctic Web sites, go to a listing by Ohio State University:
- http://polarmet.mps.ohio-state.edu/cgi-bin/catSearch.cgi
As part of its Learning Technologies Project (LTP), NASA supports a number of educational Web sites that have excellent material on the Earth sciences:- The Passport to Knowledge project, which, in its "Live From Antarctica" pages, looks at the geology, climate, biology, history, and future of this southern continent:
- http://quest.arc.nasa.gov/antarctica/passport.html
- Other LTP sites that are dedicated to the Earth sciences can be found at:
- http://observe.ivv.nasa.gov/nasa/education/edu/edudocs/topic_land.html
- http://observe.ivv.nasa.gov/nasa/education/edu/edudocs/topic_water.html