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Antarctic Ice Melt Greatest in a Millennium
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Ice on the Antarctic Peninsula
Research reveals that ice on the Antarctic Peninsula has melted at an unprecedented rate in the past 50 years and is especially vulnerable to melting in the future. Courtesy of Nerilie Abram

Researchers examine an extensive ice core from the Antarctic Peninsula and find that ice melt there is greater now than at any time in the past 1,000 years.

April 30, 2013—Researchers analyzing a 364 m long ice core drilled from the Antarctic Peninsula conclude that ice has melted there at an unprecedented rate in the past 50 years and is especially vulnerable to accelerated melting in the future; even small increases in mean temperatures from this point forward could create large, nonlinear effects on melting, they report.

Nerilie Abram, Ph.D., a research fellow at Australian National University’s Research School of Earth Sciences, led a team that conducted the research and published a report on its findings, “Acceleration of Snow Melt in an Antarctic Peninsula Ice Core during the Twentieth Century,” in the April 14 edition of the journal Nature Geoscience. In written comments to Civil Engineering online, Abram said, “As the average climate warms, more days in summer will exceed [the] melt threshold, and they will exceed it by a greater and greater amount. “This leads to a predicted nonlinear relationship between mean temperature and the amount of melting that occurs.

“Our new ice core record demonstrates that this type of nonlinear relationship has played out in the past and shows that not all of the changes that happen as climate warms are gradual, particularly where there are thresholds in the climate system,” Abram said. “For the future, the implication is that the Antarctic Peninsula has now warmed to a level where even a small further increase in temperature can lead to a large increase in the amount of melt that will occur.”

The Antarctic Peninsula is warming faster than any other place in the Southern Hemisphere, Abram said, and while it has been suggested that the series of ice shelf collapses in the region are “a visible demonstration of climate change,” she said, no one knows for certain. “Observational records are very short and sparse in Antarctica—rarely going back more than a few decades,” she said. An ice core drilling project on James Ross Island—an irregularly shaped, rugged land mass encompassing approximately 1,000 sq mi and featuring elevations of as much as 5,350 ft—was conducted in 2008 by a team led by Robert Mulvaney, Ph.D., a glaciologist with the British Antarctic Survey. This test was “designed to put the recent warming of the Antarctic Peninsula into a long-term perspective to assess how unusual the recent changes might be,” Abram explained, and its results contributed significantly to her team’s analysis of the core.

“This site had been the location of a number of drilling attempts over the past 20 years, but due to technical conditions and bad weather none of the previous attempts had managed to drill through to bedrock,” Abram explained.

Indeed, the January 2008 expedition was delayed by one month by harsh weather and technical problems, and the team members weren’t sure they could reach bedrock within the short Antarctic summer. Fortunately, aided by new drilling technology and a summer that had fewer whiteout days than expected, the team was able to compact the planned three-month project into two months, which made the process more efficient. 

 Collecting the ice core by drilling

 To collect the 364 m long ice core in the short timeframe provided
by the Antarctic summer, the team drilled in shifts so that the drill
was operating 16 hours each day. Courtesy of Nerilie Abram

“To drill the ice core we worked in shifts so that the drill was operating 16 hours each day,” Abram said. The drill was hung on a winch cable, and a motor at the top of the drill unit spun the core barrel; the weight of the drill provided the only downward force on the cable, she explained.

Each time the drill was lowered in the drill hole, it collected a sample up to 1.5 m in length. The drill was then winched to the surface, where the ice was carefully removed, and the drill was then lowered back down the hole to drill the next segment of ice. “We repeated this process over and over again until we reached rock at the bottom of the ice cap,” Abram said.

“Reconstructing the past temperature was our main aim, and it wasn’t until we started drilling and began pulling up the sections of ice where we could see these layers of past melt that we realized that this ice core could also tell us an enormous amount about summer ice melt,” she said.

“What surprised us most was that this ice core held such a unique record of ice melt history,” Abram said of the analysis of the large, complex cores. “As it turns out, James Ross Island is a ‘Goldilocks’ site for looking at ice melt—not so cold that summer temperatures are too cold for melt to occur, and not too hot that summer melting is so extensive that it destroys the climate record.

“This balance is why reconstructions of past [melts] are so rare to find; this is only the second ice core melt reconstruction produced for Antarctica,” Abram explained.

The team measured the deuterium isotope composition of the core to develop a record of mean annual temperature at the site for the past 1,000 years. By measuring the melt zones in the core, the team was able to develop a record of the annual melt intensity at the site.

The research yields a fascinating glimpse into 1,000 years of climate history in one of the world’s most unforgiving environments. The ice core reveals two pronounced periods of warming, one in the late 16th century and the other in the 18th century. It also reveals that the site was at its coldest during the period 1410–60.

“One of the big questions that remains is to understand why the Antarctic Peninsula is warming so quickly and whether this is likely to continue in the coming decades,” Abram said. “Our new ice core record provides a way to test which of the current climate models is best able to reproduce climate changes in the past, and this builds confidence in predicting future changes, including what level of ice melt could accompany any future warming.”


 

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