Isotopic and geochemical time-series from massive coral skeletons are now being used to monitor environmental changes in the oceans and nearby coastal zones. They are also being used to reconstruct the past variations in tropical surface oceanographic conditions before any records were taken. Reasearch has been focused on the skeletal oxygen and carbon isotopic composition (18O/16O, 13C/12C) as a tracer of past oceanographic conditions. The health, diversity an dextent of corals, and geochemical makeup of their skeletons, recore a variety of other changes in the oceans' surface water. These include temperature, alinity, fertility, insolation, precipitation, sea levels, storm incidence, river runoff, and human imputs. For example, corals in coastal waters are susceptible to rapid changes in salinity and suspended matter concentrations. This information can help to show the extent of effects of agriculture, urban, mining and industrial pollutnants through river systems.
Coral produces annual growht bands, very much like tree rings, which can record monthly environmental changes. The 18O/16O ratio varies as a function of temperature and salinity. In general, higher ratios imply colder temperatures, and low ratios indicate warmer conditions. Also, trace elements (Sr, Ca, Ba, and Mg), offer a wider range of what the climate is like, by recording specific features, such as upwelling of cold, deep water to the surface, runoff of freshwater from rivers, and mixing of different water masses. Radiocarbon (14C) concentrations have been used to reconstruct ocean circulation. When the deep water is brought to the surface the 14C concerntration in the coral skeleton is decreased.
|
