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 But the scientists said they have found a bacteria-killing recipe to protect the remarkable Paleolithic paintings.
The new stains are the latest biological threat to the Lascaux cave drawings, which were discovered in 1940 and are considered one of the finest examples of prehistoric art.
Carbon-dating suggests the murals of bulls, felines and other images were created between 15,000 and 17,500 years ago in the caves near Montignac, in the Dordogne region.
In 1963, after green algae and other damage appeared, the caves were closed to the public. Only scientists and a few others are allowed to enter at certain times; a replica of the main Lascaux cavern was built nearby and has become a big tourist draw.
Even those measures have not stopped the appearance of the fungus-related stains.
This July, caretakers noticed new black spots covering some of the drawings. Samples taken from them showed the stains were caused by two fungi, ulocladium and gliomastix, that developed on top of a sublayer of existing bacteria.
Targeted biocides, which are substances that can kill bacteria, were tested on the samples. At a meeting this week, the Lascaux Caves International Scientific Committee approved the use of the localized biocides to treat the affected cave areas.
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 Once that is done, the caves will be entirely closed for three months, said Michel Clement, the French Culture Ministry's top architectural and cultural heritage official.
The climate control system, which was installed in 2001 but has produced some moisture-related stains, will also be modified or replaced, the panel announced.
Just what is causing the new bacteria to appear remains unclear.
Some studies reviewed by the scientific panel suggest that global warming may be to blame.
The average natural temperatures inside the caves, measured by the climate control system, rose about 1.6 degrees Fahrenheit since 1981, according to Marc Gauthier, president of the committee.
[Associated
Press; By PIERRE SAUVEY]
Copyright 2007 The Associated
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