Long-term reconstruction of Indian Ocean Dipole variability by coral and lake sediment cores

热带和亚热带气候的变率经常被解释为不仅在太平洋而且在印度洋与ENSO有关。然而，ENSO与印度洋气候变率之间的相关性并不总是很高。最近，印度洋偶极子（IOD）被发现，它是ENSO的镜像，但独立于ENSO （Saji et al., Nature, 401,360-363,1999，随后有一系列论文）。印度洋和世界其他地区周围的许多异常气候（干旱和洪水）已显示出与IOD有关的更好理解。然而，IOD是通过仪器观测记录来分析的，这些记录通常只持续了近40年。因此，其与ENSO和季风有关的年代际和更长时间尺度的变化仍有待解决。在本研究项目中，我们打算通过珊瑚年带重建过去几十年至100年的IOD和相关气候的长期变化，并通过湖泊沉积物岩心重建过去几千年的IOD和相关气候。我们成功地从塞舌尔和肯尼亚的六个群落获得了16个珊瑚芯（最大长度：234厘米），并在埃及的Qarun湖获得了5个湖泊沉积物芯（最大长度：617.5厘米）。我们预计珊瑚岩心记录了近百年来的降水变化，湖泊沉积物岩心记录了近几千年来尼罗河流量的变化历史，两者都与IOD密切相关。岩心的分析还在进行中，但我们发现珊瑚和湖泊沉积物的岩心质量都很高。我们期望在分析结束后获得高质量的IOD变率和古气候变化记录。

Variability of tropical and subtropical climate has often been explained in relation to ENSO not only in the Pacific but also in the Indian Ocean. However, correlation between ENSO and climate variability in the Indian Ocean is not always high. Recently, Indian Ocean Dipole(IOD) was discovered, which is a mirror image but acts independently of ENSO (Saji et al., Nature, 401,360-363,1999 followed by a series of papers). Many anomalous climates (droughts and floods) around Indian Ocean and other areas of the world have shown to be better understood in relation to IOD. However, IOD has been analyzed by instrumental observation records, which usually extend only for the last 40 years. Therefore, its decadal and longer time-scale variability in relation to ENSO and monsoon remains to be solved.In this research project, we intended to reconstruct long-term variability of IOD and related climate for the last several decades to a hundred years by coral annual bands, and for the last several thousand years by lake sediment cores. We succeeded in obtaining 16 coral cores (maximum length : 234 cm) from six colonies in Seychelles and Kenya, and five lake sediment cores (maximum length : 617.5 cm) at Lake Qarun in Egypt. We expect that coral cores record precipitation changes for the last one hundred years, and that lake sediment cores record changing history of River Nile discharge for the last several thousand years, both of which are closely related to IOD. The analysis of the cores is in progress, but we have found that the quality of both the coral and lake sediment cores are very high. We expect to obtain high-quality record of IOD variability and paleoclimate change after the analysis finishes.