The Gulf of Aqaba/Eilat (GoA), Red Sea, harbors a high-latitude (29°N), yet flourishing and diverse coral reef. In spite of a normal rate of warming (~0.035°C per yr) and the occasional occurrence of extremely hot summers, no mass bleaching has ever been reported from the GoA. The local corals appear to defy the otherwise universal “heating rule” of coral bleaching. On the other hand, mass mortalities of corals occur in the GoA due to algal smothering during unusual spring blooms that follow extremely cold winters. In this talk, I will demonstrate how both phenomena are related to the unique geology and oceanography of the Red Sea, where a shallow sill (137 m) at the Straits of Bab el Mandeb controls the temperature and extent of water exchange with the Indian Ocean. Consequently, the deep Red Sea waters are unusually warm (e.g., 21°C at 2500 m depth), stratification is weak, and vertical mixing during winter reaches depths that greatly exceed any other warm-water ocean on the globe (e.g., >800 m in the cold winter after the Pinatubo eruption in 1991).
