Assessing the intercolony δ18O proxy calibration in a coral microatoll and its implication for ENSO reconstruction in the northern South China Sea

Massive Porites corals are widely used for paleoclimate reconstruction, however the potential of Porites coral microatoll delta O-18 as high-resolution archive of paleoclimate has only been recognized recently, and the systematic chemistry-climate relationship has yet to be well characterized in the western Pacific. In this study, we examined the reproducibility of microatoll delta 18o records against two adjacent Porites corals from the Xisha Islands in the northern South China Sea (SCS) and evaluated the reliability of microatoll delta O-18 as a proxy for reconstructing regional climate and El Ni no-Southern Oscillation (ENSO) variability. The seasonal to interannual variability in microatoll delta O-18 was primarily controlled by local sea surface temperature (SST), while the delta O-18 signal might be suppressed by sea surface salinity (SSS) variations on interannual timescale. Despite the overlapping coral delta O-18 records exhibited similar patterns of variability, the mean values were consistently offset by similar to 0.2% and the sensitivity of delta O-18 proxy to climate also varied across different coral colonies. The microatoll delta O-18 exhibited relatively high proxy-SST sensitivities and amplitude of the seasonal variabilities. These results suggested that intercolony delta O-18 variability was a significant source of uncertainty in coral-based paleoclimate reconstructions. Microatoll delta O-18 anomaly appeared to serve as a sensitive and relatively reliable proxy for ENSO variability, although the imprints of weak-to-moderate ENSO events could not be fully captured due to the complex relationship between the East Asian Monsoon and ENSO, as well as the local seawater salinity changes. This study further strengthened the evidence for microatoll as an alternate climate archive in the SCS and highlighted its potential in helping resolve poorly understood paleoclimate before instrumental observations.

Automated summary

This study examines the reproducibility of microatoll delta O-18 records and evaluates its reliability as a proxy for reconstructing regional climate and ENSO variability. The results show that the records are primarily controlled by local sea surface temperature, and the signal may be suppressed by sea surface salinity variations. The study highlights the potential of microatoll as an alternate climate archive in the South China Sea.