NOAA/WDS Paleoclimatology - Tahiti 9.5ka Fossil Coral Geochemical Data

The Integrated Ocean Drilling Program (IODP) Expedition 310 recovered drill cores from the drowned reefs around the island of Tahiti (17°40'S, 149°30'W), many of which contained samples of massive corals from the genus Porites. Herein we report on one well-preserved fossil coral sample: a 13.6 cm long Porites sp. dated by uranium series techniques at 9523 ± 33 years. Monthly d18O and Sr/Ca determinations reveal nine clear and robust annual cycles. Coral d18O and Sr/Ca determinations estimate a mean temperature of ~24.3°C (~3.2°C colder than modern) for Tahiti at 9.5 ka; however, this estimate is viewed with caution since potential sources of cold bias in coral geochemistry remain to be resolved. The interannual variability in coral d18O is similar between the 9.5 ka coral record and a modern record from nearby Moorea. The seasonal cycle in coral Sr/Ca is approximately the same or greater in the 9.5 ka coral record than in modern coral records from Tahiti. Paired analysis of coral d18O and Sr/Ca indicates cold/wet (warm/dry) interannual anomalies, opposite from those observed in the modern instrumental record.

综合大洋钻探计划（Integrated Ocean Drilling Program, IODP）第310次航次在塔希提岛（17°40'S，149°30'W）周边的淹没礁体中获取了钻探岩心，其中多数岩心含有团块状滨珊瑚属（Porites）珊瑚样品。本文报道一件保存完好的化石珊瑚样品：一件长13.6 cm的滨珊瑚未定种（Porites sp.），经铀系测年技术测定其年代为9523±33年。对该样品开展的月分辨率氧同位素比值（δ¹⁸O）与锶钙比（Sr/Ca）分析显示出9个清晰且稳定的年周期。基于珊瑚δ¹⁸O与Sr/Ca的估算结果显示，距今9.5 ka的塔希提海域平均海水温度约为24.3℃（较现代偏低约3.2℃）；但该估算结果需谨慎看待，因为珊瑚地球化学记录中可能存在的冷偏差成因仍有待厘清。该9.5 ka珊瑚的δ¹⁸O年际变率特征，与附近莫雷阿岛的现代珊瑚记录相似。该9.5 ka珊瑚的Sr/Ca季节循环振幅与塔希提现代珊瑚记录相当，甚至更强。对珊瑚δ¹⁸O与Sr/Ca的配对分析显示，其年际异常呈现冷湿（暖干）的特征，与现代器测记录观测到的结果截然相反。