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ICE WORLD
Current ice melt rate in Pine Island Glacier may go on for decades
by Anne M Stark for LLNL News
Livermore CA (SPX) Feb 25, 2014


A massive crack rus about 29 kilometers (18 miles) across the Pine Island Glacier's floating tongue, marking the moment of creation for a new iceberg that will span about 880 square kilometers (340 square miles) once it breaks loose from the glacier. Lawrence Livermore research shows that the glacier's recent melt may go on for decades or centuries. For a larger version of this image please go here.

A study of the Pine Island Glacier could provide insight into the patterns and duration of glacial melt. The Pine Island Glacier, a major outlet of the West Antarctic Ice Sheet, has been undergoing rapid melting and retreating for the past two decades.

But new research by an international team including researchers from Lawrence Livermore National Laboratory shows that this same glacier also experienced rapid thinning about 8,000 years ago.

Using LLNL's Center for Accelerator Mass Spectrometry to measure beryllium-10 produced by cosmic rays in glacially transported rocks, Lawrence Livermore researchers Bob Finkel and Dylan Rood reported that the melting 8,000 years ago was sustained for decades to centuries at an average rate of more than 100 centimeters per year. This is comparable to modern-day melting rates.

The findings indicate that modern-day melting and thinning could last for several more decades or even centuries. The research appears in the Feb. 20 issue of Science Express.

"Pine Island Glacier has experienced rapid thinning at least once in the past. Once set in motion, rapid ice sheet changes in this region can persist for centuries," said Finkel, one of the authors of the new findings.

Ice mass loss from the Pine Island-Thwaites sector dramatically contributes to the sea level of the West Antarctic Ice Sheet. The Pine Island Glacier is currently experiencing significant acceleration, thinning and retreat.

The rate of thinning from 2002-2007 on the grounding line (the part where the glaciers export the ice down the continent and lose contact to the ground and become a floating ice shelf) was between 1.2 meters per year and 6 meters per year.

The change is likely tied to the increased influx of warm water to the cavity under the ice shelf at the glacial front.

Dramatic changes over longer timescales -- from centuries to millennia -- are somewhat limited, so there is considerable uncertainty associated with model projections of the future evolution of timing and ice loss of the Pine Island Glacier.

Current geological research is tied to the grounding line retreat across the continental shelf. However, little is known about the terrestrial thinning history and how the ice stream evolved from 8,000 years ago to the onset of present-day thinning.

The team found that there was a direct correlation from glacial-geological samples consisting of cobblestones and granite boulders from the Hudson Mountains to rapid thinning in the Pine Island Glacier system about 8,000 years ago.

"The melting of the Pine Island Glacier at a rate comparable to that over the past two decades is rare but not unprecedented," Rood said. "Ongoing ocean-driven melting of the glacial ice shelf in current times may result in continued rapid thinning and ground line retreat for several more decades or even centuries."

Other institutions involved in the research include: The British Antarctic Survey; Durham University; University of California, Berkeley; University of California, Santa Barbara; Alfred Wegener Institute Helmholtz-Centre for Polar and Marine Research; Berkeley Geochronology Center; Lamont-Doherty Earth Observatory; and Columbia University.

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Related Links
Center for Accelerator Mass Spectrometry at LLNL
Beyond the Ice Age






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ICE WORLD
Study predicts Antarctic ice melting will endure
Washington (AFP) Feb 20, 2014
The melting of ice in the Antarctic is considered a top threat to global sea level rise, and scientists said Thursday the trend could continue for decades or even centuries to come. Researchers focused on the Pine Island Glacier in Antarctica, which has been thinning at an increasingly rapid pace for about the past 20 years, as the waters beneath get warmer along with the rest of the ocean. ... read more


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