Seasonal rainfall in the Sinai Desert during the late Quaternary inferred from fluorescent bands in fossil corals

Abstract

SKELETAL bands of alternating high and low density in massive coral species have been used to record their growth history^1,2. In the Red Sea, living colonies of the genus Porites deposit low-density skeletal bands during summer and high-density bands during winter³. Additionally, yellow-green fluorescence can sometimes be seen in these massive corals, imparted to them by the incorporation of humic material carried by coastal runoff⁴. Annual banding of fluorescent sequences in living scleractinian corals has proved to be useful in the study of terrestrial runoff in the near-shore environment^5,6. Here we report the finding of similar yellow-green fluorescent bands in fossil Porites from late Quaternary reef terraces in southern Sinai, which are absent from living Porites in the nearby fringing reefs. The periodic sequences of the fluorescing humics were found to be superimposed on the low-density sub-bands of the fossil corals. We interpret our observations as evidence that, during the late Quaternary reef-forming peaks, the climate was wetter than the extreme desert conditions now prevailing, with a possible summer rainfall regime.