Response of upper ocean structure to the initiation of the North Hemisphere glaciation in the South China Sea

摘要

Planktonic foraminifer as well as oxygen and carbon isotopic records from Ocean Drilling Project Core 1146, located at the northern continental slope of the South china Sea, were used to study the response of the upper water column structure to the formation and progressive intensification of the Northern Hemisphere glaciation during the Late Pliocene (3.2-2.0 Ma). Variations in the relative abundance of the Globigerinoides ruber, Globigerinoides sacculifer, Globorotalia menardii, and Globorotalia inflata groups, Globorotalia crassaformis and Neogloboquadrina pachyderma showed that sea surface temperatures gradually decreased, coinciding with heavier oxygen isotope values at 2.8,2.72,2.6,2.5,2.16, and 2.08 Ma. After 2.7 Ma, the relative abundance of mixed-layer species decreased, while that of thermocline dwellers, dominated by high productivity species, increased. Δδ~(13)C variations among G. sacculifer, pulleniatina obliquiloculata and Cibicidoides wuellerstorfi suggest that the mixed-layer depth and vertical exchange was enhanced with the strenghtening of the East Asian winter monsoon, which in turn is associated with the progressive intensification of the Northern Hemisphere glaciation.