The Toba tephra layer has been identified in core MD972151 in the southern South China Sea (SCS), northeast of the Indonesia Toba caldera. This affords us an opportunity to directly determine a 1 degreesC cooling for ca.l kyr on the SCS following the Toba eruption (71 Ka) during the marine isotope stage 5a-4 transition, using century-scale sea surface temperature records. This cooling event in the SCS is well correlated with several coeval proxies such as increased East Asia winter monsoon intensity, increased ice-rafted detritus in the North Pacific Ocean sediments, and decreased delta O-18 in Greenland ice core. Such correlation suggests a climate change where cold climate signals originated in the Northern Hemisphere ice sheets, transferred southward by the winter monsoon, and cooled the SCS.