( Rising sea levels 20000 years ago as ...)Ice core 'dipstick' indicates West Antarctic ice has thinned less than believed

But in a new study led by University of Washington researchers, an ice core of 1,000 meters was used as a sort of dipstick to show that a key section of the West Antarctic Ice Sheet probably never contained as much ice as scientists originally thought it did. That means it couldn't have contributed as much to the higher sea level.

In an area called Siple Dome, the ice sheet currently rises 1,000 meters -- more than half a mile -- above a bedrock plateau. Some computer reconstructions indicate it was perhaps twice as thick at the end of the last ice age, also called the Last Glacial Maximum.

But evidence from an ice core extracted near Siple Dome from 1997-99, along with other calculations, indicates ice in that area has lost only 200 to 400 meters of its thickness in the last 20,000 years, said Edwin Waddington, a UW professor of Earth and space sciences.

Like water on a hillside, Siple Dome ice flows down into adjacent ice streams, where it continues to the nearby Ross Ice Shelf, a part of a bay on the Ross Sea that is covered with floating glacier ice.

"Then the whole thing spreads out like oil on water," Waddington said.

The West Antarctic Ice Sheet once rested on the bottom of the bay all the way to its "grounding line" at the continental margin in the Ross Sea. However, that ice has retreated substantially in the last 20 millennia, at the same time Siple Dome was thinning. Part of the puzzle has been whether the ice streams were flowing, whether they carried interior ice to the ice shelf at the end of the last ice age, and whether they began where they do now or receded along with the ice shelf's grounding line.

Studying the ice core layer by layer, each representing one year's worth of snowfall compacted into a very thin band, researchers were able to extract an isotope
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Source:University of Washington