Western Antarctica & Antarctic Ice Shelves

Eric Leibensperger

EPS 131

Antarctica

• 98% covered by ice• Remaining 2% barren

rock• Covered with about 70%

of the Earth’s fresh water• Averages only 1-3 inches

of snow fall each year• Much of land below sea

level (ice is heavy!)

Western Antarctica• Contained in Western Hemisphere• Transantarctic mountains create

barrier between Western and Eastern Antarctica

• Warmer than larger Eastern Antarctica

• Includes Antarctic Peninsula and 100s of islands

• Land beneath West Antarctic Ice Sheet mostly under sea level

Antarctic Ice Sheets• Thought to be 35 million years old• Ice sheet on average 2.5 km thick

• Ice sheets cover land, ocean and lakes

• West Antarctic Ice Sheet (WAIS)

Ice Shelves

• Ice slides off the coast and begins to float• The buoyancy of the ice holds glaciers and ice

sheets in place• Generally 100-1000 m thick

Problem!

• Ice shelves have been thinning and breaking into the ocean

• Without the ice shelves, ice sheets and glaciers can retreat into the ocean with greater ease.

• 250 billion tons of ice fall into the ocean causing a sea level rise of .2 mm each year (10% of yearly increase of sea level)

Possible Mechanism of Ice Shelf Breaking:

• Increased sea temperatures and air temperatures cause melting and cracking

• Melt ponds form

• Water seeps into cracks in the ice

• When water freezes again, it creates larger cracks

• Destruction of shelves takes many thawing and freezing seasons

Larsen A and B Shelf Collapses

• In Jan. 1995, Larsen A Ice Shelf collapsed

• In 2002, numerous collapses occurred at the Larsen B Ice Shelf

Results of Ice Shelf Collapses

• Glacier ice lost into the ocean is greater than newly deposited snow by 60%

• It is estimated that the total loss of glacier ice from all ice shelf removal could be up to 5m!

• Remember: ice produced from ice shelf collapses DO NOT increase sea level since they are already floating in the ocean. The addition of ice from the mainland increases the sea level.

Whose fault is it?

• Global temperature increase (2.5ºC over last century)

• Most likely from global climate change induced by anthropogenic effects

• Additional global increases in temperature will cause further shelf collapses and more ice sheet and glacial ice introduction into the ocean

• Something to keep an eye on!

References

Hogan, J. (2005), Antarctic Ice Sheet is an ‘Awakened Giant’, NewScientist, http://www.newscientist.com/article.ns?id=dn6962

Lincoln, T. (2004), Global Change: Glacial Pace Picks Up, Nature, 431, 519.

National Snow and Ice Data Center, http:// nsidc.org

Scientists Report Increased Thinning of West Antarctic Glaciers, NASA Top Story, http://www.nasa.gov/centers/goddard/news/topstory/2004/0923westglaciers.html

Shepard A., et al. (2004), Warm Ocean is Eroding West Antarctic Ice Sheet, Geophysical. Research Letters., 31, 255-258.