Fidelity of δ¹⁸O as a proxy for sea surface temperature: Influence of variable coral growth rates on the coral Porites lutea from Hainan Island, China

The extremely high temporal resolution (nearly daily interval) measurement was conducted on the coral ( Porites lutea ) oxygen isotope compositions (δ 18 Oc) to examine the detailed relationship between δ 18 Oc and sea surface temperature (SST) and seawater oxygen isotope composition (δ 18 Ow) from Hainan Island, China. Although SST and sea surface salinity (SSS) or δ 18 Ow varied in a wide range at the studied site, the dynamic range of δ 18 Oc recorded in coral was much smaller than expected from SST and SSS (δ 18 Ow) changes. The extremely high (>30°C) and low (<22°C) SST and low (<27) SSS are not suitable for coral calcification, and coral could not record the information as their skeletal δ 18 O. Estimated coral extension rates (the overall rate is 15 mm/year) varied by a factor of about 18 within one year, from very slow in winter to very fast in spring. Light availability could affect the extension rate of coral skeleton through the activity of photosynthesis of symbiont algae. Such cessation and acceleration of calcification cause a serious distortion of the δ 18 O profile, which makes it difficult to make a correlation between δ 18 O and SST. Because high and low extension rates correspond to low‐ and high‐density bands, respectively, a detailed examination of the density structure may assist the correction for distortion of the δ 18 O profile.