Altamira cave art: low-vent district?

Altamira cave art: Low-vent district?

The Altamira cave near Santander, Spain, is famed for its "Paintings Room,," a chamber decorated with Stone Age paintings from more than 10,000 years ago. The cave was closed to visitors in 1977, however, due to deterioration of the artworks presumably caused in some way by the constant stream of tourists.

Scientists at the University of Santander now report that the wearing away of paleolithic paint and its limestone backing may have been promoted by carbon dioxide exhaled by people inside the chamber. Carbon dioxide buildup can lead to the dissolution of limestone. An initial charting of natural ventilation in the Paintings Room indicates it is weak and thus allows carbon dioxide to collect even without humans present, write physicist P. L. Fernandez and his colleagues in the June 5 NATURE.

The researchers measured the concentration of radon gas in the chamber three times per week from February 1983 through January 1984. This, they say, is the best available means to assess ventilation. Radon escapes to the atmosphere through cracks in the earth, they note, and concentrates in the air of places with little ventilation. While ventilation of radon is weak throughout the year in the Paintings Room, it is lowest in May and peaks in July.

Furthermore, say the researchers, the carbon dioxide concentration in the Paintings Room, which originates from gas dissolved in underground waters, is at its lowest during July, August and September, and speaks in May and November. Taking into account the estimated average volume of carbon dioxide exhaled by one person, the scientists calculated the maximum number of people who could visit the cave or one hour each day in the summer months without raising the carbon dioxide level beyond the peak seen in May: 43 in July, 74 in August and 80 in September. The number of daily visitors in the summer was considerably greater before the cave was closed.