Warm years are good years for trees growing high on mountains. Recovery of environmental information from trees is now so sophisticated and advanced that it has become the science of dendroclimatology. None of these gives good information about tropical ocean regions. A source of proxy information for such regions would fill a large gap in the existing proxy records. Annual density bands in coral skeletons have promised to be the tropical marine proxy record since their discovery 20 years ago.
Extensive records are possible because some corals live for several hundred years.
Density bands offer records in themselves, analogous to tree rings, and they offer a means to analyse human impact upon coral reef ecosystems. Moreover, the bands make it possible to date the time at which skeleton was deposited. The skeleton includes a variety of trace materials taken up from the coral's environment. The outermost dark density band was formed during the 1986-1987 summer. Counting backwards, the coral probably started growing in 1966.