VERTICAL MIXING AND CORAL DEATH IN THE RED-SEA FOLLOWING THE ERUPTIONOF MOUNT-PINATUBO

THE eruption of Mount Pinatubo in the Philippines led to a cold air-te mperature anomaly throughout the Middle East during the winter of 1992 (1). Here me report that the vertical mixing in the Gulf of Eilat (Aqa ba) that winter was unusually deep--extending to >850 m--resulting in increased supply of nutrients to surface waters, which fuelled extraor dinarily large algal and phytoplankton blooms. By spring, a thick mat of filamentous algae covered broad sections of the underlying reef cau sing extensive coral death. Branching colonies and solitary mushroom c orals were most severely affected. This sequence of events, in which a short-term atmospheric cooling leads to a remarkable ecological respo nse, is made possible by the unusually weak water-column stratificatio n of the Gulf of Eilat. The depth of local vertical mixing during wint er is determined by the net heat loss across the sea-air interface, so that anomalously cold winters drive the deeper mixing that can lead t o increased phytoplankton blooms. Records of such events in fossil ree fs may provide useful indicators of past variations in regional air te mperatures.