Timing coral-based climatic histories using ¹³C enrichments driven by synchronized spawning

High-resolution measurements of the skeletal ¹³C/¹²C ratios of massive Porites corals from the Great Barrier Reef and eastern Indian Ocean reveal ¹³C enrichments culminating sharply at the time of the annual coral spawning event. These ¹³C skeletal enrichments appear to be driven by the rapid sequestering of ¹²C required to build the reproductive tissue prior to spawning. Coral spawning is commonly synchronized with the lunar phase and, in this case, is predictable to within 3 days. The results suggest that reproductive modulation of ¹³C/¹²C can be exploited as an accurate, built-in time marker for constructing realistic time series with proxy climate data extracted from corals. Recognition of the ¹³C/¹²C response to reproduction also facilitates the separation of physiological and environmental influences and should expand the utility of stable carbon isotopes in paleoceanography.