Scientists are studying a greater reduction than usual this winter in the ozone layer and debating whether it signals a worrisome trend for the protective screen.

Each winter, the Northern Hemisphere's ozone layer thins, but measurements this year indicated the depletion has spread to previously unaffected areas."We have an indication, not a proof, that these `miniholes' are indeed the first sign of a depletion of the ozone layer caused by manmade activities," said Swedish atmospheric physicist Andre Zuber Friday.

But a Finnish meteorologist who recorded the latest "minihole" over Finland said it is a natural phenomenon that does not represent a serious depletion of the ozone layer.

"It's nothing to worry about," said Esko Kyro, who works at a meteorological station in Sodanyla in northern Finland.

Ozone screens hazardous ultraviolet radiation from the sun. Excess exposure can lead to skin cancer and other problems.

Measured in Dobson units, an ozone reading of about 350 is typical. Kyro said that he measured 220 Dobson units on Tuesday, the lowest ever recorded in Finland.

Levels of about 200 Dobson units were recorded in the past two years over Oslo, Norway, and Norrkoping, Sweden.

The ozone is believed to be affected by chlorofluorocarbons, a manmade chemical often used as an aerosol propellant.