Analyses of foraminiferal δ18O (δ18Ocarb), δ13C (δ13Ccarb) and bulk organic matter (δ13Corg) across a tropical Eocene/Oligocene boundary (EOB) section from Kutch basin, western India show that the ocean cooling (at least ~3¿C) is coincident with a rapid enrichment (~3?) in δ13Corg but depletion (~1.5?) in δ13Ccarb. The decrease in pCO2 in ocean-atmosphere system across the boundary, possibly resulting from enhanced silicate weathering in rising Himalayas and accompanied organic carbon burial in ocean, caused the cooling and δ13Corg enrichment. The end-Eocene climatic stress decreased the oceanic productivity (and δ13Ccarb) eventually causing extinction of larger benthic foraminiferal community. The data suggest a critical role of tropical ocean and direct forcing of CO2 on global climate change at least for this crucial Cenozoic transition.