Yellowknife (Apr 11/03) - The murky bottoms of Yellowknife area lakes is offering biologists clear evidence for the global warming trend said to be affecting the North.

Various diatoms, single cell algae that scientists can read like "a history book," have been flourishing in Northern lakes after being non-existent here for 5,000 years. - photo courtesy of Kathleen Rulhand

Scientists collected mud samples during the mid-'90s from 50 lakes outside Yellowknife and all the way up to the Arctic Ocean to study the remains of fossilized algae.

Queen's University biologist John Smol said the data collected is providing some of the best evidence yet that the world is warmer now than it has been for 5,000 years.

"Virtually everything that lives in the lake is leaving some sort of remains in that mud and our job as paleoecologists is to remove that history book and to interpret the information that's preserved in those archives," said Smol.

Algae that flourishes with long periods of open water has thrived in the past century, but it was non-existent for the previous 5,000 years.

"To make a long story short we saw a marked ecological change in these lakes in the period that we studied," he said.

"The easiest explanation is global warming."

The study looked at thousands of tiny single-celled algae called diatoms collected in 1996 to 1997 by doctoral student Kathleen Ruhland who works with Smol.

When the diatoms died they sank to the bottom of the lake and were preserved in the mud. Scientists can put an approximate date on when the diatoms died by measuring how deep in the mud they are.

Some diatoms live in lakes that stay frozen for most of the year, others require long periods of open water.

The numbers of warm-water algae increased rapidly in the years where industrial activity worldwide also rose, said Smol.

"This only really started happening within the past 100 years," he said.

The study will be published this month in the Arctic, Antarctic and Alpine Research journal.