Stable oxygen isotope record from a high-latitude reef off Western Australia

A core from a coral colony of Porites lutea was analysed for stable oxygen isotopic composition*. A 200-year proxy record of sea surface temperatures from the Houtman Abrolhos Islands off west Australia was obtained from coral delta18O. At 29°S, the Houtman Abrolhos are the southernmost major reef complex of the Indian Ocean. They are located on the path of the Leeuwin Current, a southward flow of warm, tropical water, which is coupled to Indonesian throughflow. Coral delta18O primarily reflects local oceanographic and climatic variability, which is largely determined by spatial variability of the Leeuwin Current. However, coherence between coral delta18O and the current strength itself is relatively weak. Evolutionary spectral and singular spectrum analyses of coral delta18O demonstrate a high variability in spectral composition through time. Oscillations in the 5-7-y, 14-15-y, and quasi-biennial bands reflect teleconnections of local sea surface temperature (SST) to tropical Pacific climate variability. Deviations between local (coral-based) and regional (instrument) SST contain a cyclic component with a period of 15 y. Coral delta18O suggests a rise in SST by 0.6°C since AD 1944, consistent with available instrumental SST records. A long-term warming by 1.4°C since AD 1795 is inferred from the coral record.

本研究对一株澄黄滨珊瑚（Porites lutea）的珊瑚岩芯开展了稳定氧同位素组成（stable oxygen isotopic composition）*分析。研究基于西澳大利亚州外海霍特曼·阿布洛霍斯群岛（Houtman Abrolhos Islands）的珊瑚δ¹⁸O（原文标注为delta18O）数据，重建了时长200年的海表温度代用记录。该群岛地处南纬29°，是印度洋最南端的大型礁体复合体。其位于勒温海流（Leeuwin Current）的流经路径之上——勒温海流是一支携带温暖热带水体向南流动的洋流，与印尼贯穿流（Indonesian Throughflow）存在耦合关联。珊瑚δ¹⁸O主要反映局地海洋与气候变率，而该变率在很大程度上由勒温海流的空间变异所主导。但珊瑚δ¹⁸O与勒温海流强度本身的相关性相对较弱。对珊瑚δ¹⁸O开展的演化频谱分析与奇异谱分析（Singular Spectrum Analysis）结果显示，其频谱构成随时间呈现出显著变化。周期为5~7年、14~15年以及准两年的振荡信号，反映了局地海表温度（Sea Surface Temperature, SST）与热带太平洋气候变率之间的遥相关（teleconnections）关系。局地（基于珊瑚重建的）与区域（仪器观测的）海表温度之间的偏差，存在一个周期为15年的周期性分量。珊瑚δ¹⁸O记录显示，自公元1944年以来，海表温度上升了0.6℃，这与已公开的仪器观测海表温度记录相一致。基于珊瑚记录可推断，自公元1795年以来，区域海表温度长期变暖幅度达1.4℃。