Satellite observations reveal a substantial weakening of the southeasterly trade wind over the South Indian Ocean during 1992--2000 and a resultant slowdown of the shallow meridional overturning circulation in this Ocean. The estimated rate of the slowdown of this circulation, 6.8 ¿ 1.4 ¿ 106 m3/s over the 9-year period, is nearly 70% of the mean strength of this circulation. Such a change has important implications to upper-ocean heat content and decadal climate variability of the Indian Ocean, as well as to the ecosystem and air-sea exchange of CO2 in the region.