COCCOLITH EVIDENCE FOR VARIATIONS IN UPPER OCEAN WATER IN UPWELLING AREA OFF THE COAST OF VIETNAM FOR THE PAST 450 000 YEARS

Florisphaera profunda is one of the lower euphotic zone species of coccolithophores. Using its percentage we can reconstruct the variations in the upper ocean water such as the depth of nutricline and the primary productivity. Coccolith analysis has been carried out for the past 450 ka sediment from core MD05-2901 off the Vietnam coast in the western South China Sea. The results show that the depth of nutricline and primary productivity of surface water have experienced significant changes. The spectral analysis indicates that the percentage of F. profunda is influenced by low latitude process such as precession and half-precession. Comparison of F. profuuda percentage and primary productivity between the present core and ODP Site 1143 of the southern South China Sea indicates that the two sites have a similar trend in the upper ocean water change since 450 ka which are controlled by changes of Asian monsoon and orbital forcing.