Flora changes as the Arctic warms.

The Arctic's ecosystem fell prey to global warming earlier than previously thought, a research team now argues.

For thousands of years, the patterns of plant life in Arctic ponds changed very little and only very gradually. But in the 1800s, these patterns shifted dramatically, probably as a result of warming temperatures, a study of frozen sediment cores from Arctic ponds reveals.

Marianne S.V. Douglas of the University of Massachusetts at Amherst and her colleagues analyzed the fossilized remains of diatoms, a type of algae, from three ponds on Ellesmere Island in the Canadian Arctic, they report in the Oct.21 SCIENCE. Their core samples dated back as much as 8,000 years.

One genus of diatom dominated two of the ponds until the 19th century, the team says. Then, in one of those ponds, a diatom that lives on moss swelled from 10 percent of the diatom population to 90 percent of it, the team reports.

At the other pond, the flora shifted completely, to a relatively diverse mixture of six diatoms, the scientists find. The third pond's recent sediments reveal "dramatic increases" in the relative frequency of one genus of diatom, they discovered.

The authors ruled out airborne pollution, changes in ultraviolet radiation, or activities of local inhabitants as possible causes for the shifts in the abundance of the single-celled organisms. The culprit, they suspect, is global warming. Even a slight increase in temperatures would extend the growing season and allow for changes in diatom communities.

Other researchers have also found signs of Arctic temperature increases, but "our data indicate an earlier (by over a century) start for these changes," Douglas and her colleagues say. Some scientists, however, believe that the Arctic shows no signs of warming (SN: 1/30/93, p.70).