Reefs are associations of living organisms (biocoenosis), among which the long living calcified ones, like corals and molluscs provide excellent archives to reconstruct past environmental conditions and changes. Their skeletal record of the paleoenvironment comprises not only regional but global signals covering large spatial areas and time spans. The tropics receive more than two thirds of the global sun radiation and tropical atmospheric anomalies, like El Niño impact on the global climate. Coral reefs are widespread in the tropical shallow water environments and may be addressed as one of the most productive carbonate factories within the benthic ecosystems. Some of the tropical corals, mainly the massive colonies, form annual density bands comparable to tree rings. These massive colonies may live for more than several centuries. Their annual growth is documented in these density bands und provides an excellent calendar to study the seasonal signal of geochemical parameters used as proxies for environmental variability to reconstruct the times before reliable instrument data are available.
The distribution of coral reefs is not restricted to the tropics. The cold water corals occurring in higher latitudes do not live in symbiosis with algae, like their tropical “relatives”. Therefore, they are not light dependant and as a consequence, almost independent from depth. The occurrence of cold and deep water reefs is known for more than two decades. These cold water coral reefs can be found along most of the worlds continental margins in a depth between 1000m and 40m. Calcified cold water corals are very good recorders of environmental variability as well. The exploration of this new archive to reconstruct intermediate watermass dynamics on a seasonal scale is one of the major focal points of the paleoceanography group at GEOMAR | Helmholtz-Zentrum für Ozeanforschung Kiel. The environmental factors controlling the occurrence and distribution of these reef building corals are still a major topic to be studied.