Image: ¿BRITISH ANTARCTIC SURVEY
Antarctic lakes may be the most sensitive harbingers yet of the effects of the earth's changing climate, scientists say. According to a study published in the current issue of the journal Science, lakes on Antarctica's Signy Island (see image) have experienced a temperature increase nearly three times greater than that of the surrounding air. Furthermore, the average amount of time each year that the lakes were frozen over decreased by more than four weeks between 1980 and 1993. Such trends, the researchers write, "indicate that local climate change has been translated into extreme ecological change."
Wendy Quayle of the British Antarctic Survey (BAS) and colleagues studied 17 lakes located on Signy Island, which lies at the junction of the Weddell and Scotia Seas. Such polar lakes can serve as early detectors of environmental change, the team notes, because variations in snow and ice cover markedly affect their ecological variables. Indeed, according to co-author Lloyd Peck, "the pristine nature of Antarctic lakes gives us a unique natural laboratory where we can identify changes that are undetectable in contaminated lakes."
The researchers determined that the mean winter temperatures of nine of the lakes increased by as much as 1.3 degrees Celsius¿two to three times the increase recorded for air temperature in the region. Sea temperatures surrounding the region, in contrast, stayed the same. The lakes' temperature increases are tied to the number of days the lakes remain free of ice, because without an icy covering, the water absorbs more solar radiation. Over a 15-year period, the amount of time that the lakes spent frozen over each year declined, on average, by 31 days. The ecosystems within the lakes were also profoundly affected, the scientists report. Specifically, the phosphate content of the lakes increased by 10 times over the study period, in part as a result of increased melt-water runoff traveling over thawed ground instead of glacier ice. "There is now three times the amount of chlorophyll from algae in the lake than there was 20 years ago," Quayle notes.
The study represents yet another small piece in the complex puzzle of Antarctica's response to climate change. Its findings seem to contradict those of another study, published two weeks ago in the journal Nature, which found that parts of Antarctica's dry desert regions are cooling instead of warming. But because the two study regions lie almost 4,000 miles apart, regional variations are not entirely surprising. "In recent decades, we've seen a complex picture of temperature change over the whole Antarctic continent," explains John Turner, a BAS meteorologist and co-author of the new study. "What we can say with certainty is that Antarctica is extremely sensitive to environmental change."