Thursday, October 27, 2005

Global warming evidence in remote northern lakes

Lake algae confirm global warming link (29 October 2005)

ALGAL growth in remote Arctic lakes is confirming what ecologists suspected all along - that entire freshwater ecosystems are altering in response to climate change.

Neal Michelutti and his colleagues at the University of Alberta in Edmonton collected 30-centimetre core samples from the bottom of six lakes on Baffin Island in the Canadian Arctic. From levels of chlorophyll a in the sediment, which they measured using a technique called reflectance spectroscopy, they deduced that plant life in the lakes began to increase 150 years ago and is now growing almost exponentially year by year.

The most likely reason for the change is climate warming, Michelutti says. Cycles of plant and alga growth in the lakes last only a few weeks, and lengthening that period by even a few days would be noticeable in the sediment, he says.

Past experiments have failed to show a convincing link, either because they covered too short a geological period or because they were conducted in areas where human activity could have affected the results. The core samples of Michelutti's experiment contain 5000 years' worth of data from an area almost untouched by human activity.

"These are pristine lakes that mankind hasn't directly affected," he says. "But there has definitely been an indirect effect."
From issue 2523 of New Scientist magazine, 29 October 2005, page 19