ResearchMWatch An ice sheet–climate change connection?
sponding to climatic changes that occurred thousands of years ago. (Nature 2001, 414, 60–62)
Ice breakup is due to thermal (melting) and dynamic effects (ice movement upriver). A warmer climate is expected to advance the occurrence of these effects and therefore the time of ice breakup. Sagarin and Micheli looked for long-term trends in the record and compared these with available climatic data for the town of Nenana and Fairbanks. The magnitude of ice breakup advancement, 5.5 days at Nenana, is similar to what has been found in other phenological records, they say. According to the researchers, the contest is scientifically valuable because it is based on a very consistent definition of ice breakup. (Science 2001, 294, 811).
JULIE COGHILL, SOLAR POWER PRESS
The ice sheet in northwest Greenland has been thinning over the past 40 years, according to researchers Stan Climate change? You bet! Paterson of Paterson Geophysics in Heriot Bay, British Columbia, and For centuries, naturalists, hobbyists, Niels Reeh of the Technical University and indigenous peoples throughout of Denmark, in Lyngby, who report the world have recorded naturally octhinning rates that are significantly curring events that are indicative of faster and extend to higher elevations the effects of weather and changing than have been anticipated from preseasons. Until recently, however, the vious studies. value of such observations for underThe researchers’ findings are standing global climate change has based on direct measurements of surbeen discounted as unscientific. But face elevation changes over the perisuch data are an important source of od 1954–1995 on a traverse across the information and should not be nenorth Greenland ice sheet. In contrast glected, contend Raphael Sagarin and to the significant thinning on the Fiorenza Micheli of Stanford University. west side of the ice sheet, some thickTo demonstrate the importance of ening of the north ice stream has ocphenological observations, the scienFast acid-volatile sulfide test curred on the eastern part of the tists evaluated an 84-year data set on transect, but there has been little the timing of ice breakup on the An inexpensive, versatile analysis change across the midsection. Tanana River, near Fairbanks, Alaska. method that quickly determines Accounting for climate change efThe data, they say, show temporal amounts of acid-volatile sulfide (AVS) fects on sea level rise requires a good patterns consistent with previously in sediment pore waters has been understanding of the thermal expanreported climatic trends toward an developed by Stuart Simpson at the sion of oceans, glacial melting, and earlier spring. Commonwealth Scientific & Industrial changes in ice caps and Research Organisation in sheets. The new findings Australia. AVS is an important fill a significant void: indicator of the bioavailabiliThe largest uncertainties ty of toxic trace metals and is in forecasting sea level increasingly being used to changes are associated predict the toxicity of metalwith estimates of the contaminated sediments. mass balance of the Simpson’s new method is Greenland and direct and requires minimal Antarctica ice sheets. equipment. A small sediment The reported obsersample is simply placed in vations, say Paterson distilled water, methylene and Reeh, span a long blue—an indicator of AVS— enough period of time is added, and the sample is to assure that what they centrifuged. On standing for Clim ate change issignaled bythe advancing date on w hich thistridetermined is ice sheet 90 minutes, the resulting inpod collapses. thinning and not fluctudicator color change estabations in snow cover. Because of the The eight decades-long database lishes the amount of AVS present. complexity of the processes that can was obtained from the records of the Although the method is 10 times occur in this region of the world, reliNenana Ice Classic, an annual betting less sensitive than more commonly able measurements are essential. For contest held in Nenana, Alaska, in used purge-and-trap methods and example, referring to an earlier study which participants vying for a prize in underestimates AVS by about 20%, it by Huybrechts and Le Meur (Polar excess of $300,000 hope to guess the is fast, requires much smaller samples Res. 1999, 18, 299–306), the scientists exact minute in spring when, due to for analysis, and is readily deployable note that, in addition to other effects, ice breakup, a tripod positioned on in remote field situations. (Environ. the Greenland ice sheet is still rethe frozen river will collapse. Toxicol. Chem. 2001, 20, 2657–2661) JANUARY 1, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY I 19 A
