Using sediment core and oxygen isotope analysis, researchers have recently proved that Larsen B -- which disintegrated in 35 days in 2002 -- had been a stable ice shelf 200 metres thick with a surface area of 3,250 square kilometres for at least 10,000 years. By contrast the Larsen A Ice Shelf, which broke up in the 1990s, was absent for a significant part of that period and reformed beginning about 4,000 years ago, according to the study.
"The disintegration of Larsen B is almost certainly a response to human-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 25 years. By comparison, the world-wide temperature change during the entire post-glacial period has only been 2 -- 3°C," he adds.
Larsen B's demise is likely the consequence of long-term thinning due to melting from underneath as well as short-term surface melting due to global warming. The "under melt" of a few tens of metres over thousands of years is caused by warming waters or currents flowing beneath the floating ice shelf. However, the surface melting has happened much faster over decades, the study concludes. And Larsen B's demise could set off a series of environmental changes.
"The breaking up of Larsen B alone will not change sea level, but other glaciers previously restricted by the ice shelf have surged forward, lowering their surfaces," says Dr. Gilbert. "Lower elevations have warmer temperatures, which warm the glaciers and cause more melt and more flux of ice to the sea. So that is having and will have an effect on global sea levels. As more ice is lost there may be a greater impact on sea level than previously predicted.
"Further, with the increased energy in the atmosphere associated with global warming, there will be more storms," he warns. "Storm surges, which also raise water levels, will have profound effects on low-lying areas and may necessitate infrastructure like the large moveable dams called surge gates already used in Europe and Providence, R.I., that can be closed during extreme high sea levels to prevent flooding."
Although other, smaller ice shelves have undergone periodic decay and growth since the last ice age, these small ice shelves exist at the climatic limit for ice shelf formation and would be expected to respond quickly to climate change over hundreds and thousands of years, the study indicates.
The research team also includes scientists from Hamilton College in New York State, Colgate University, the Lamont-Doherty Geological Observatory at Columbia University, Montclair State University in New Jersey and Southern Illinois University.
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