The Indian Ocean Dipole (IOD), an oscillation of sea surface temperatures in the Indian Ocean, has become a major influence on the weather variations in the Indian Ocean region. During positive IOD events, abnormally warm sea surface temperatures in the western Indian Ocean are accompanied by severe droughts over the Indonesian region and heavy rainfall over east Africa.

To learn more about IOD patterns, Nakamura et al. studied a 115-year coral record from Kenya. They analyzed coral oxygen isotope ratios, which trace rainfall anomalies, to reconstruct IOD variability. The results add to evidence that the IOD has been occurring more frequently in recent decades. The researchers find that before 1924, the IOD occurred approximately every 10 years, but since 1960, IOD events have been occurring approximately 18 months to 3 years apart.

The authors suggest that global warming effects on the western Indian Ocean have driven the observed shift in IOD variability and note that the IOD has replaced the El Niño-Southern Oscillation as the major driver of climate patterns over the Indian Ocean region.

The research is published in Geophysical Research Letters. Authors include Nobuko Nakamura, Hajime Kayanne, Hiroko Iijima, and Toshio Yamagata: Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan; Timothy R. McClanahan: Marine Programs, Wildlife Conservation Society, New York, New York, USA; and Swadhin K. Behera: Frontier Research Center for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan.

(ScienceDaily*, 30/12/2009)

*Adapted from materials provided by American Geophysical Union, via EurekAlert!, a service of AAAS.

Journal Reference:

   1. Nakamura et al. Mode shift in the Indian Ocean climate under global warming stress. Geophysical Research Letters, 2009; 36 (23): L23708 DOI: 10.1029/2009GL040590