The scale of the change that we're seeing is greater than predicted

Dr Cynun Ellis-Evans

The scientists who carried out the research say the study provides more evidence of extreme changes in the Antarctic Peninsula region, which has warmed up faster than almost anywhere on Earth - an increase of 2.5 degrees C in the last 50 years.

A team from the British Antarctic Survey (Bas) has been looking at the temperature and chemistry of the lakes on Signy Island, which lies at about 60 degrees south, just off the tip of the peninsula.

Summer air temperatures there have increased by about one degree C between 1981 and 1995. At the same time, the number of days where the lakes are free of ice cover has increased by about one month.

Not predicted

In addition, the researchers say that estimates from photographs indicate that permanent ice cover on the island has reduced by 45% since 1950. They say this has "radically affected" the island.

Signy has a number of freshwater lakes

The effect of the increasing air temperature on the chemistry and biology of the lakes has taken scientists by surprise. Dr Cynun Ellis-Evans, one of the team who carried out the work, says: "Over 20 years, the lake temperatures have increased by almost three times the increase in local air temperature over the same period.

"So what we're seeing is that the heat is being drawn into the lakes, being stored there and building up to have a magnified effect.

"The chemistry and microbial processes in the lakes are increasing substantially," he adds. "The scale of the change that we're seeing is greater than predicted and substantially higher than current global climate models are predicting for systems in the polar regions."

Useful lessons

The ecology of the lakes has been altered by an increase in their exposure to the Sun, and as a result of the introduction of nutrients transported there by glacier melt-water flowing over exposed ground.

Signy Island lies at the confluence of the ice-bound Weddell Sea and the warmer Scotia Sea

A 10-fold increase in the amount of phosphate has acted as a natural fertiliser, allowing algae to flourish. There is now three times the amount of chlorophyll from algae in the lake than there was 20 years ago.

Professor Lloyd Peck of the British Antarctic Survey said these lakes were the first to undergo such rapid changes in the Antarctic, but that he expected similar changes would be seen in lakes further towards the South Pole if warming in the region increased.

Changes were also taking place in lakes in northern Europe and in America. "Understanding what happens when there's a rapidly changing environment is likely to be very useful to us in years to come when there are similar rapid changes in Western Europe, too," he added.