Ice Shelf Disintegration Threatens Environment, Queen's Study

Using sediment core and oxygen isotope analysis, researchers haverecently proved that Larsen B -- which disintegrated in 35 days in 2002-- had been a stable ice shelf 200 metres thick with a surface area of3,250 square kilometres for at least 10,000 years. By contrast theLarsen A Ice Shelf, which broke up in the 1990s, was absent for asignificant part of that period and reformed beginning about 4,000years ago, according to the study.

"The disintegration of Larsen B is almost certainly a response tohuman-induced global warming," says Queen's geographer Robert Gilbert,the only Canadian researcher on the international research team."Antarctic temperatures have increased more than 10°C in the last 25years. By comparison, the world-wide temperature change during theentire post-glacial period has only been 2 -- 3°C," he adds.

Larsen B's demise is likely the consequence of long-term thinning dueto melting from underneath as well as short-term surface melting due toglobal warming. The "under melt" of a few tens of metres over thousandsof years is caused by warming waters or currents flowing beneath thefloating ice shelf. However, the surface melting has happened muchfaster over decades, the study concludes. And Larsen B's demise couldset off a series of environmental changes.

"The breaking up of Larsen B alone will not change sea level, but otherglaciers previously restricted by the ice shelf have surged forward,lowering their surfaces," says Dr. Gilbert. "Lower elevations havewarmer temperatures, which warm the glaciers and cause more melt andmore flux of ice to the sea. So that is having and will have an effecton global sea levels. As more ice is lost there may be a greater impacton sea level than previously predicted.

"Further, with the increased energy in the atmosphere associated withglobal warming, there will be more storms," he warns. "Storm surges,which also raise water levels, will have profound effects on low-lyingareas and may necessitate infrastructure like the large moveable damscalled surge gates already used in Europe and Providence, R.I., thatcan be closed during extreme high sea levels to prevent flooding."

Although other, smaller ice shelves have undergone periodic decay andgrowth since the last ice age, these small ice shelves exist at theclimatic limit for ice shelf formation and would be expected to respondquickly to climate change over hundreds and thousands of years, thestudy indicates.

The research team also includes scientists from Hamilton College in NewYork State, Colgate University, the Lamont-Doherty GeologicalObservatory at Columbia University, Montclair State University in NewJersey and Southern Illinois University.