Warmer Ocean Could Threaten Antarctic Ice Shelves

Focus 766 768 774 SARS Looking for When friends search long-term become sputters survivors parasites

GLACIOLOGY Warmer Ocean Could Threaten Antarctic Ice Shelves When two chunks of ice the size of a small summer meltwater includes snow that re- country broke off the Antarctic Peninsula’s freezes into denser ice, fell through when the Larsen Ice Shelf in 1995 and 2002, experts team calculated that the shelf doesn’t receive scrambled to figure out how it had happened. enough solar energy to drive that process. The pat answer, global warming, was too sim- “The temperature is just not enough to pro- ple: Some parts of Antarctica are cooling, and vide that amount of melt,” Shepherd says. the soaring air temperatures along the penin- That suggests melting from below. Al- sula that seemed to have triggered the collapse though there are no long-term ocean tempera- have not yet been convincingly linked to a ture data from the Larsen shelf, deep waters worldwide pattern. But as a model for what farther out in the Weddell Sea have been could happen elsewhere in Antarctica as tem- warming over the past 3 decades, Shepherd’s peratures rise, it was crucial to understand the team notes. Also, a BAS ship sailing near the Larsen Ice Shelf’s demise. Larsen shelf in 2002 detected midlevel tem- Now a detailed look at the Larsen’s peratures warm enough to melt ice at that shrinking ice is challenging conventional depth. At the current melting rate, the Larsen wisdom about the collapse. Andrew Shep- will reach the breaking point within this cen- Cold discomfort. The Larsen Ice Shelf is herd, a glaciologist at the University of Cam- tury, Sheperd’s team predicts. imperiled from above and below. bridge, U.K., and co-workers analyzed satel- Others caution that the findings are not lite data to produce the first estimate of how that solid; the satellite data are imprecise, rapher Stan Jacobs of the Lamont-Doherty quickly the Larsen Ice Shelf is thinning. Scambos notes, and there is no direct evi- Earth Observatory in Palisades, New York. They report on page 856 that since 1992, the dence that ocean waters off the Larsen have These larger shelves hold back massive thinning has been too fast for rising air tem- warmed. But if the results hold up, the study aboveground ice sheets that would dramati- DIA/CORBIS peratures to explain. They conclude that the will serve as a wake-up call that larger ice cally raise global sea level if they melted. shelf must be melting due to warmer ocean shelves on mainland Antarctica may also be “It’s a good model for what could happen,” waters below. If so, the rest of the Larsen is vulnerable to ocean warming, says oceanog- Jacobs says. –JOCELYN KAISER doomed, and other Antarctic ice shelves could be more endangered than had been FORENSIC GEOCHEMISTRY thought. “We need to understand the poten- tial for other ice shelves to be hit,” says Isotopic Data Pinpoint Iceman’s Origins glaciologist David Vaughan of the British Antarctic Survey (BAS) in Cambridge, U.K. The renowned Alpine Iceman, known as Plant matter in his intestine had suggested Researchers were stunned when the Ötzi, has proven to be an extraordinarily rich that the Iceman spent his final days in an Larsen’s two roughly Luxembourg-sized source for researchers interested in life dur- area south of where he was found in 1991, northern sections abruptly shattered, each ing the late Neolithic era. They know Ötzi’s sticking out of melting snow near the moun- breakup taking just a few weeks. Suspicion age, his health, his mitochondrial DNA se- tainous border between Italy and Austria. fell on air temperatures on the peninsula, quence, what he ate, and how he died. But Now researchers have used isotopic signa- which for a half-century have risen by 0.5°C where did he live? tures from teeth and bones to pinpoint his a decade, 10 times faster than the global origins to a few valleys in south- trend. Glaciologist Ted Scambos of the Na- ern Tyrol; they report their find- tional Snow and Ice Data Center in Boulder, ings on page 862. They say Ötzi Colorado, and co-workers have suggested probably did not stray more than that summertime pools of meltwater on the 60 kilometers from his birth- Larsen Ice Shelf eventually force crevasses place until his death more than apart and lead to collapse. Image not 5000 years ago. But Shepherd’s study suggests that al- available for Wolfgang Müller of Australian though air temperatures may strike the final National University in Canberra, blow, they can’t be the whole story. He and online use. who began the research 3 years colleagues at the U.K.-funded Centre for Po- ago while at the Swiss Federal In- lar Observation and Modelling and in Ar- stitute of Technology, and an in- gentina quantified the thinning using satel- ternational team cleverly used lite radar measurements of the shelf’s height various parts of Ötzi’s body and corrected for tides. They found that the shelf three kinds of isotopes to trace his thinned by up to 18 meters between 1992 Hard data. The Iceman’s teeth and bones indicate where he whereabouts during his lifetime. ▲

CREDITS: TO ARGENTINO AND P.BOTTOM) ANTÁRTICO (TOP S. AÉREA ARGENTINA; SKVARCA/INSTITUTO TOJEIRO/FUERZA WERNER NOSKO/REUTERS NEWME and 2001. One possible explanation, that the spent his youth and later years. “It’s a marvelous paper,” says