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

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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.