Department of Natural History Sciences, Faculty of Science, Hokkaido University, Sapporo, 060-0810, Japan.
KIKAI Institute for Coral Reef Sciences, Kikai town, 891-6151, Japan.
Sci Rep. 2019 Feb 13;9(1):1887. doi: 10.1038/s41598-018-38429-y.
The Indian Ocean Dipole (IOD) is an interannual mode of climate variability in the Indian Ocean that has intensified with 20 century global-warming. However, instrumental data shows a global-warming hiatus between the late-1990s and 2015. It is presently not clear how the global-warming hiatus affects modes of climate variability such as the IOD, and their basin-wide ocean-atmosphere teleconnections. Here, we present a 26-year long, biweekly record of Sr/Ca and δO from a Porites coral drilled in the Gulf of Oman. Sea surface temperature (SST) is calculated from Sr/Ca ratios, and seawater δO (δO) is estimated by subtracting the temperature component from coral δO. Our δO record reveals a significant regime shift in 1999, towards lower mean δO values, reflecting intensified upwelling in the western Indian Ocean. Prior to the 1999 regime shift, our SST and δO show a clear IOD signature, with higher values in the summer of positive-IOD years due to weakened upwelling. The IOD signature in SST and δO disappears with the overall intensification of upwelling after the 1999 regime shift. The inferred increase in upwelling is likely driven by an intensified Walker circulation during the global-warming hiatus. Upwelling in the Western Indian Ocean uncouples from the IOD.
印度洋偶极子（IOD）是印度洋中一种年际气候变化模式，随着 20 世纪全球变暖而加剧。然而，仪器数据显示，在 20 世纪 90 年代末至 2015 年期间存在全球变暖暂歇。目前尚不清楚全球变暖暂歇如何影响气候变化模式，如 IOD 及其全流域海洋-大气遥相关。在这里，我们提供了来自阿曼湾开采的珊瑚中 26 年长、每两周记录的 Sr/Ca 和 δO。海表温度（SST）是根据 Sr/Ca 比计算的，海水 δO（δO）是通过从珊瑚 δO 中减去温度分量来估算的。我们的 δO 记录显示，1999 年发生了显著的状态转变，向更低的平均 δO 值转变，反映出印度洋西部上升流的增强。在 1999 年状态转变之前，我们的 SST 和 δO 显示出明显的 IOD 特征，由于上升流减弱，正值 IOD 年份的夏季 SST 和 δO 值较高。在 1999 年状态转变之后，随着上升流的整体增强，SST 和 δO 中的 IOD 特征消失。上升流的增加很可能是由于全球变暖暂歇期间沃克环流的加强所致。西印度洋的上升流与 IOD 脱耦。
