TIMING CORAL-BASED CLIMATIC HISTORIES USING C-13 ENRICHMENTS DRIVEN BY SYNCHRONIZED SPAWNING

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