Regime shift of skeletal δ¹³C after 1997/1998 El Nino event in Porites coral from Green Island, Taiwan

The 1997/1998 El Niño event caused mass coral bleaching and mortality in many tropical and subtropical regions, including corals on Green Island, Taiwan, in the northwestern Pacific Ocean. This study analyzed coral carbon isotope ratios (δ¹³C), oxygen isotope ratios (δ¹⁸O), and Sr/Ca ratios for 29 years, including the 1997/1998 El Niño period, to examine how high water temperature events are recorded in coral geochemical indicators. Sr/Ca ratios in coral skeletons from Green Island show the lowest peak, means the highest temperature during the 1997/1998 El Niño period. However, we couldn’t observe high-temperature events on δ¹⁸O. Furthermore, a negative δ¹³C shift was observed after El Niño events. The regime shift of δ¹³C might have been caused by temporal bleaching and/or a decrease in symbiotic algae due to high water temperature stress under the continuous decrease in δ¹³C in DIC due to the Suess effect.