High frequency of 'super-cyclones' along the Great Barrier Reef over the past 5,000 years.

Understanding long-term variability in the occurrence of tropical cyclones that are of extreme intensity is important for determining their role in ecological disturbances, for predicting present and future community vulnerability and economic loss and for assessing whether changes in the variability of such cyclones are induced by climate change. Our ability to accurately make these assessments has been limited by the short (less than 100 years) instrumented record of cyclone intensity. Here we determine the intensity of prehistoric tropical cyclones over the past 5,000 years from ridges of detrital coral and shell deposited above highest tide and terraces that have been eroded into coarse-grained alluvial fan deposits. These features occur along 1,500 km of the Great Barrier Reef and also the Gulf of Carpentaria, Australia. We infer that the deposits were formed by storms with recurrence intervals of two to three centuries, and we show that the cyclones responsible must have been of extreme intensity (central pressures less than 920 hPa). Our estimate of the frequency of such 'super-cyclones' is an order of magnitude higher than that previously estimated (which was once every several millennia), and is sufficiently high to suggest that the character of rainforests and coral reef communities were probably shaped by these events.