Paired Porites coral Sr/Ca and δ18O from the western South China Sea: Proxy calibration of sea surface temperature and precipitation

• Combined inter-coral Sr/Ca lower root mean square residual of reconstructed SST
• Sr/Ca from Vietnam coral reconstructs SST with an error as low as ± 0.39 °C.
• Coral δ18Osw values reflect precipitation over 3-year averaged timescales.

Paired strontium-to-calcium (Sr/Ca) and δ18O measurements for two Porites lutea corals recovered from Hon Tre Island, Vietnam, are strongly correlated to sea surface temperature (SST) and precipitation at monthly to interannual time-scales. Least squares linear regression of monthly Sr/Ca to SST shows a strong, significant correlation (r2 = 0.77, p < .0001), with root mean square residuals of 0.9 °C. 3-year averaged (binned) Sr/Ca for wet (Sep–Nov) and dry (Jan–Mar) seasons separately captures SST variability at interannual time scales (Sr/Ca RMSR = 0.42 °C and 0.70 °C for wet and dry seasons, respectively). Coral δ18O correlates weakly to SST at seasonal and interannual time scales for wet and dry seasons, with significant anomalies (δ18O RMSR = 2.4 °C and 1.65 °C, respectively). Correcting the SST influence on coral δ18O using paired Sr/Ca values provides estimates of δ18O of seawater (δ18Osw). 3-year averaged δ18Osw during the wet season shows a significant correlation to local precipitation (r2 = 0.54, p = 0.01). These results show that coral Sr/Ca in this location accurately reflects SST at a number of timescales, and that seawater δ18O composition in the wet season is controlled by local precipitation, largely unmodified by ocean circulation during the winter monsoon. This study highlights the sensitivity and utility of coral geochemistry in this region for reliably reconstructing SST and monsoonal precipitation.