Paired Porites coral Sr/Ca and δ~(18)O from the western South China Sea: Proxy calibration of sea surface temperature and precipitation

摘要

Paired strontium-to-calcium (Sr/Ca) and δ~(18)O 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 (r~2 = 0.77, p b.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 δ~(18)O correlates weakly to SST at seasonal and interannual time scales for wet and dry seasons, with significant anomalies (δ~(18)O RMSR = 2.4 °C and 1.65 °C, respectively). Correcting the SST influence on coral δ~(18)O using paired Sr/Ca values provides estimates of δ~(18)O of seawater (δ~(18)O_(sw)). 3-year averaged δ~(18)O_(sw) during the wet season shows a significant correlation to local precipitation (r~2 = 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 δ~(18)O 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.