Smoke signals from corals: isotopic signature of the 1997 Indonesian ‘haze’ event

From September to November 1997, most of Indonesia was covered by a dense blanket of haze, originating from fires on Sumatra and Borneo. Specimens of Porites lobata were collected from two locations, i.e. the Riau Archipelago, south of Singapore, where the haze was most dense, and the Karimunjawa Islands, north of Central Java, where the effects were less severe. All corals exhibited strong Kinetic Isotope Effects (KIE). On plots of δ18O vs. δ13C, shifts in coral metabolism associated with the haze event could be estimated from the distance individual values are positioned from the theoretical KIE line. Skeletons of corals affected by the haze showed decreased δ13C values, perhaps produced by a shift to a more heterotrophic mode of feeding. These results suggest that wildfires and major forest fire events on tropical coastlines may be recorded in nearby corals, as could temporal variation in frequency of major fires. Moreover, information on coral metabolism may be determined by examining shifts of coral skeletal values in C–O space.