March 18, 2009
Climatologists Gain Insight From Massive West Antarctic Melt
Two new reports published in the journal Nature illustrate possible flooding due to climate change and a meltdown of the massive West Antarctic ice sheet.
In one study, researchers used soil cores below the Ross ice shelf to show that the massive melt took place between 3 million and 5 million years ago. That collapse amounted to an increase of more than 16 feet to global sea level, researchers noted.
Warm waters appear to be continually chipping away at the West Antarctic ice sheet, but recent activity is nothing compared to the historic collapse, researchers say.
Authors of the soil core study say a complete collapse of west Antarctica will take hundreds, if not more than a thousand, years to take place.
According to the AP: "One paper suggested that temperatures would have to rise 9 degrees to trigger a complete collapse in West Antarctica, although the study authors said that was a rough estimate. Leading global scientists have suggested a 9-degree temperature rise is a possibility by 2100."
In another study, researchers created computer models to illustrate that warm waters apparently attacked the ice shelf from below.
"We found that the West Antarctic ice sheet varied a lot, collapsed and regrew multiple times over that period," said David Pollard, senior scientist, Penn State's College of Earth and Mineral Sciences' Earth and Environmental Systems Institute. "The ice sheets in our model changed in ways that agree well with the data collected by the ANDRILL project."
"We found, as expected, that the East Antarctic ice sheet is stable and did not change," said Pollard.
Pollard worked alongside Robert M. DeConto, professor of climatology at the University of Massachusetts.
They found that the East Antarctic ice shelf does not slide into the sea and melt away because most of the bedrock below East Antarctic ice is above sea level. However, on the other side of the continent, to the Pacific side of the Transantarctic Mountain Range, much of the bedrock below the ice lies from several hundred to several thousand feet below sea level, leaving the West Antarctic ice vulnerable to melting.
"We found that the ocean's warming and melting the bottom of the floating ice shelves has been the dominant control on West Antarctic ice variations," said Pollard.
The researchers compared their model's output with the sediment core record from ANDRILL. In these cores, coarse pebbly glacial till represent the glacial periods, while intervals filled with the shells of tiny ocean-living diatoms represent the nonglacial periods. One way the ANDRILL researchers date the layers is using existing datable volcanic layers within the core.
"Our modeling extends the reach of the drilling data to justify that the data represent the entire West Antarctic area and not just the spot where they drilled," said Pollard.
Researchers warn that in the past, carbon dioxide levels were about 400 parts per million, in the early part of the ANDRILL record. West Antarctic ice sheet collapses were much more frequent.
"We are a little below 400 parts per million now and heading higher," said Pollard.
"One of the next steps is to determine if human activity will make it warm enough to start the collapse."
On the Net: