The Rainy Season

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Science  16 Feb 2001:
Vol. 291, Issue 5507, pp. 1159-1161
DOI: 10.1126/science.291.5507.1159f

Asian monsoons are powered by the difference in heating of the Tibetan Plateau and Indian Ocean during the year. Monsoons likely have occurred ever since the uplift of the Tibetan Plateau, but the precise age of that event has been controversial. Dettman et al. used stable isotope analyses from freshwater bivalve shells and mammal teeth in deposits from the paleo-Indus and paleo-Ganges rivers to examine the history of seasonal variations in rainfall. They find a pattern of pronounced wet and dry seasons, characteristic of a strong monsoon, throughout at least the past 10.7 million years, although the climate 7.5 million years ago was particularly dry. Nevertheless, the monsoon has persisted during periods of major changes in Earth's climate and in ocean circulation. Monsoon intensity does vary and has been linked to the longer El Niño cycles; Kudrass et al. describe how these events affect weather globally. — BH

Geology29, 31 (2001); Geology29, 63 (2001).

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