SCIENCE

Notebook

Siberian Lakes Disappearing

Lakes in northern Siberia are shrinking and disappearing at a steady rate as the Arctic climate warms and permafrost thaws, and none of the lakes have been refilling.

Using satellite photos of north-central Siberia taken from 1972 to 1998, researchers found that the number of large lakes in a 220,000-square-mile region had declined by 1,170, or more than 11 percent. Each of the lakes studied was larger than 100 acres.

During the 26-year period, total lake coverage in that area decreased by more than 6 percent, even though precipitation increased slightly.

Writing in Friday's issue of the journal Science, the researchers concluded that "the ultimate effect of continued climate warming on high-latitude, permafrost-controlled lakes and wetlands may well be their widespread disappearance." Of the almost 11,000 Siberian lakes that shrank significantly, the researchers found, 125 lakes disappeared entirely and were refilled with vegetation.

Permafrost is ground ice that generally does not melt throughout the year. There are, however, gradations of permafrost, ranging from conditions where the soil remains ice cold from the surface on down all the time, to situations where some surface permafrost melts and where nearby areas experience thawing during warm spells.

The researchers said that although the Siberian region they studied saw an overall and substantial decline in the number of lakes, the more northern reaches of "continuous" permafrost experienced an increase. The reason, the researchers hypothesized, is that as permafrost warms, it slumps and collapses -- creating depressions (thermokarst) where water collects as lakes. But if the warming continues, they said, the thermokarst in the northern reaches will go through the same shrinking process now seen at the more southern lakes and will gradually disappear.

-- Marc Kaufman

Asian Settlers a Small Group

A Rutgers University geneticist studying the original migration of colonists from northern China to the New World more than 10,000 years ago has determined that these first settlers numbered as few as 70 people.

Evolutionary geneticist Jody Hey devised a complex model to describe how one population can split into two, then fueled it with data from nine genetic sequences common to both Native Americans and northern Asians.

What he found was a surprisingly small "effective," or childbearing age, population of about 70 individuals, who broke away from an ancestral Asian community of 9,000 to cross the Bering Strait land bridge to the Americas about 14,000 years ago.