The dominant modes of climate variability on interannual timescales in the tropical Indian Ocean are the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole. El Niño events have occurred more frequently during recent decades, and it has been suggested that an asymmetric ENSO teleconnection (warming during El Niño events is stronger than cooling during La Niña events) caused the pronounced warming of the western Indian Ocean. In this study, we test this hypothesis using coral Sr∕Ca records from the central Indian Ocean (Chagos Archipelago) to reconstruct past sea surface temperatures (SSTs) in time windows from the mid-Little Ice Age (1675–1716) to the present. Three sub-fossil massive Porites corals were dated to the 17–18th century (one coral) and the 19–20th century (two corals). Their records were compared with a published modern coral Sr∕Ca record from the same site. All corals were subsampled at a monthly resolution for Sr∕Ca measurements, which were measured using a simultaneous inductively coupled plasma optical emission spectrometer (ICP-OES). Wavelet coherence analysis shows that interannual variability in the four coral records is driven by ENSO, suggesting that the ENSO–SST teleconnection in the central Indian Ocean has been stationary since the 17th century. To determine the symmetry of El Niño and La Niña events, we compiled composite records of positive and negative ENSO-driven SST anomaly events. We find similar magnitudes of warm and cold anomalies, indicating a symmetric ENSO response in the tropical Indian Ocean. This suggests that ENSO is not the main driver of central Indian Ocean warming.

中文翻译：

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自1675年以来热带印度洋的厄尔尼诺现象-南方涛动与内部海表温度的变化

热带印度洋年际尺度上气候变化的主要模式是厄尔尼诺-南方涛动（ENSO）和印度洋偶极子。厄尔尼诺事件在最近几十年中更加频繁地发生，并且有人提出，ENSO的不对称遥相关（厄尔尼诺事件期间的变暖比拉尼娜事件期间的变冷要强）导致了西印度洋的明显变暖。在这项研究中，我们使用中印度洋（Chagos群岛）的珊瑚Sr recordsCa记录检验了这一假设，以重建从小冰河世纪中期（1675–1716）到现在的时间窗内过去的海面温度（SST）。 。三个子化石大规模 滨珊瑚的历史可以追溯到17至18世纪（一种珊瑚）和19至20世纪（两种珊瑚）。他们的记录与来自同一地点的已发布的现代珊瑚Sr ∕ Ca记录进行了比较。以每月分辨率对所有珊瑚进行Sr ∕ Ca采样使用同步电感耦合等离子体发射光谱仪（ICP-OES）进行的测量。小波相干分析表明，四个珊瑚记录的年际变化是由ENSO驱动的，这表明自17世纪以来，印度洋中部的ENSO-SST遥相关一直是固定的。为了确定厄尔尼诺事件和拉尼娜事件的对称性，我们编制了正负ENSO驱动的SST异常事件的复合记录。我们发现冷暖异常的幅度相似，表明热带印度洋的ENSO响应对称。这表明ENSO并不是印度洋中部变暖的主要驱动力。