Responses of foraminiferal isotopic variations at ODP Site 1143 in the southern South China Sea to orbital forcing

The foraminiferal delta(18)O and delta(13)C records for the past 5 Ma at ODP Site 1143 reveal the linear responses of the Plio-Pleistocene climatic changes in the southern South China Sea to orbital forcing at the obliquity and precession bands. The phase of the 5180 variations with the orbital forcing is opposite to that of the delta(13)C, which may be caused by the frequent El Nino events from the equatorial Pacific. The amplification of the Northern Hemisphere Ice Sheet at similar to3.3 Ma probably affected the development of the 100-ka climatic cycles. Its further spreading may spur the 100-ka climatic cycle to become the dominant cycle in the late Pleistocene. The "Mid-Pleistocene Transition" event has localized influence on the isotopic variations in the southern South China Sea. The foraminiferal delta(13)C records for the past 5 Ma at Site 1143 are highly coherent with the orbital forcing at the long eccentricity band, and lead the delta(18)O records at the shorter eccentricity band, highlighting the importance of the carbon cycle in the global climate change.