Corals as a climate diary
Henry C. Wu heads the Coral Climatology working group at the Leibniz Center for Tropical Marine Research (ZMT) in Bremen. In an interview with "Spektrum" he explains why coral reefs are important archives of our recent climate history.
Mr. Wu, what do corals tell us about the climate of the past?
Henry C. Wu: At the Leibniz Center for Tropical Marine Research (ZMT) we work with hard corals that form structures up to five meters in size. These so-called massive corals can become "Image" for a good 500 years and continue to grow. In doing so, they filter nutrients and other dissolved substances from the seawater, the composition of which is stored in their skeleton in this way. Thus, they record the temperature and salinity of the ocean. The advantage of corals is that they allow us to understand seasonal changes. Some grow 1.5 centimeters per year - which is pretty fast for these animals. Analyzing every millimeter of the skeleton yields a monthly resolved climate history. alt="
How exactly does this "coral thermometer" work?
Hard corals are composed of calcium carbonate (CaCO3). During growth, they incorporate dissolved carbon dioxide (CO2) and water molecules (H2O) into their calcareous skeleton. The composition of the oxygen isotopes changes depending on the temperature and salinity. The heavy oxygen isotope 18O accumulates in the ocean because H2O molecules with the lighter isotope 16O evaporate faster. Thus, the skeleton of a coral reflects the environmental conditions at the time it grew. So it indicates if the ocean was colder or warmer, more or less saline…
