Tree Rings Coral Rings
Ice Cores Lakes and Ponds, Varves, and Pollen

Corals record climate in a very similar way to trees – by annual rings of growth that are recorded by their calcium carbonate (CaCO3) skeleton. As the corals grow, the ring patterns record a year’s growth, and is similar to annual tree rings in that it can record a good growing season or bad growing season. The animal grows in both winter and summer, but the density of the seasonal skeletons is quite different. This is due to seasonal changes in ocean temperature, availability of nutrients, and differences in light. Additionally, the coral rings contain carbon molecules that indicate not only the richness of their diet but also the climatic conditions at the time! 


A coral reef in the south Pacific. Photo credit: Christina Kellogg, USGS.


In order to understand how corals can assist in climate research it is necessary to understand what a coral is, and how it lives.  Corals, of the sort that form a coral reef, are a colonial organism, which means they live large interdependent communities in warm, shallow, salty, ocean waters. These communities live on a thick base, up to hundreds of meters thick, of calcium carbonate skeletons (ultimately known as limestone) of earlier communities, with the living polyps only found on the top few millimeters.

The polyps secrete a calcium carbonate “cup” in which the soft bodied organism lives. The community of cups eventually becomes “cemented” together and form an interconnected network of coral exoskeleton (skeleton on the Outside.)  When the polyps die, the skeleton degrades and allows a new layer of living polyps to attach to the reef.

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