Heterogeneity of coral skeletons isotopic compositions during the 1998 bleaching event

The vulnerability of coral reefs to climate change, such as regional warming, became fully evident during the strong 1997-1998 El Niño event. This El Niño episode was associated with elevated sea-surface temperatures and caused mass mortality throughout many of the world's coral reefs. We analyzed the isotopic manifestation of this event in six Porites sp. coral skeletons from different localities in a small atoll (Alphonse) at the Seychelles Island. The aim was to validate the use of coral stable isotope compositions as recorders of such events in the past. The coupling between local-scale environment and global warming was weaker then expected, with regional warming being evident only when data from five colonies were averaged. Local conditions had a large effect on the isotopic compositions of coral skeletons. We conclude that future paleoclimate reconstructions, especially those attempts to identify past El Niño events, must be based on more than a single coral record. Moreover, the strong effect of local habitat on the isotopic composition of Porites sp. has to be considered when interpreting δ¹³C and δ¹⁸O records.