Coral tells of wetter times in desert.

Coral tells of wetter times in desert

While rain is rare in the Sinai desert these days, an analysis of fossil coral indicates the region was much wetter 100,000 years ago, Israeli and Australian researchers report in the May 10 NATURE.

R. Klein of Tel Aviv University and his colleagues studied terraces of ancient coral reefs along the shores of the Red Sea. Analysis of the corals revealed about 15 to 25 times the concentration of humic acid found in modern coral from the Red Sea. Humic acid is a chemical that comes from organic material in soils.

The fossil reefs grew during geologically brief interglacial periods separating the most recent ice ages. To explain the high humic acid concentrations, the researchers propose the Sinai received much more rainfall during previous interglacial periods than it does today. The rain would have washed humic acid into the sea, where it would enter the bodies of growing coral.

Klein and his co-workers believe they can even pinpoint the time of year when the rains fell. Viewed under an ultraviolet light, the fossil coral shows distinct fluorescent bands with high humic content alternating with nonfluorescent bands with lower humic content. Comparisons with modern coral indicate the fluorescent bands correspond to summer growth, which means the Sinai had a summer rainy season. Similar analyses of fossil coral could help reveal the climate history of other regions around the globe, the researchers say.