Environmental and Climate Proxies Embedded in Coral Skeletons

Scleractinian (hard layered) corals live for several centuries or longer in the tropical surface waters that comprise about half of the total surface area of the world’s oceans. Coral reefs in the tropical surface waters are the largest biologically produced natural features over the Earth’s surface. About 20% of modern carbonate accumulation takes place in coral reefs. The relatively thick annual growth bands of coral skeleton (usually around 10 mm a year) have provided a wealth of information on the climate and environmental changes that occurred in the past. These environmental archives are becoming essential to forecast the future climate and environmental changes in their local habitats in the tropical regions including the Indo-Pacific Warm Pool region that plays a significant role in the world ocean and atmospheric circulation, hence in the entire globe. Deep-sea scleractinian corals often living more than a millennium have been found in most oceans, and these slow-growing corals (a few micron meters a year) have also been found to faithfully record climate and environmental changes that occurred in the ocean. This chapter introduces the status of the scientific investigation on a coral skeleton climate and environmental proxies to the audience who are interested in coral reef with respect to climate and environmental change. It will briefly cover the biomineralization process, methods of sampling coral cores and subsequent cleaning for further chemical analysis, skeleton age determinations, and the utilities of selected chemical elements and selected isotope proxies (Li, B, C, N, O, F, Na, Ca, V, Cr, Mn, Fe, Ni, Cu, Zn, Y, Mo, Cd, I, Ba, REEs, Nd, Pb, U, Pu). This chapter is largely dealt with surface-dwelling tropical corals, but it also includes some proxy studies on deep corals.