British researchers have found large quantities of natural ozone-depleting chemicals in Antarctica.

Chemists from the University of Leeds, the University of East Anglia and the British Antarctic Survey reported finding high concentrations of halogens, such asbromine and iodine oxides.

"The springtime peak of iodine oxide [20 parts per trillion] is the highest concentration recorded anywhere in the atmosphere," said an abstractof their study, published in the journal Science on Thursday.

The bromine came from sea salt and the iodine from"almost certainly bright orange algae that coat the underside of the sea ice around the continent," they said in a release.

Halogensdeplete theozone above the ice surface, which reduce the capacity of the atmosphere to remove certain chemical compounds.

"We still have to work out what the ramifications of this discovery are," said John Plane, professor of atmospheric chemistry at the University of Leeds.

The chemistsdidan 18-month study of the lowest part of the atmosphere on the Brunt Ice Shelf, about 20 kilometres from the Weddell Sea.

The scientists projecteda beam of light across the shelf, and analyzed thelevels of chemicals in the reflected light. Moreover, satellite observations byteam memberAlfonso Saiz-Lopez"have confirmed that iodine oxides are widespread throughout coastal Antarctica."

The scientists are planningadditional studies toassess the impact on the local environment.

The finding may raise questions about the belief that chemicals made by humans are behind the disappearance of ozone over the continent.

The ozone layer is the part of the atmosphere 25 kilometres up that acts as a shield protecting life on Earth from damaging UV rays, which can cause sunburns, skin cancer and cataracts. The rays can also harm marine life.

The layer has decreased globally by about 0.3 per cent per year. The loss is seen as a hole over the South Pole because of atmospheric and wind conditions during the southern winter.

The hole grows during the winter, peaking in the southern spring, and is seen until the summer in November or December.

It is a common belief that chlorofluorocarbons (CFCs) produced by humans are breaking down theozone layer. For example, the UN Environment Programme Ozone Secretariat said in 2006 the depletion of the ozone over Antarctica "cannot be explained by natural cycles but is caused by the impact of synthetic chemicals in the stratosphere."

CFCs were banned under the Montreal Protocol in 1987. In August 2006, the UN group said the ozone layer could return to pre-1980 levels by 2049 over much of the world, but it would take until 2065 to restore the shield over Antarctica.