Coccolithophores are one of the most abundant and widespread groups of calcifying plankton and have attracted extensive study in terms of their likely response to ocean acidification. Conflicting results concerning coccolithophore calcification have been reported from both experimental and field studies. Due to their minute size, it is difficult to estimate the amount of calcite in coccoliths. Here we apply the SYRACO system to analyzing the weights and lengths of coccoliths produced by the dominant coccolithophore family Noëlaerhabdaceae. We obtain high-resolution coccolith weight and length records of GEO (Gephyrocapsa oceanica) and SPC (Emiliania huxleyi and small Gephyrocapsa spp.) groups from sediment core MD05-2901 in the western South China Sea (SCS) over the past 450 kyr. A calcification index (k value) based on the coccolith weight and length is applied to evaluate the changes in coccolithophore calcification. The two groups of coccolith k value show opposite patterns on long term variations due to the coccolith assemblages evolution. By applying polynomial regressions to exclude the long term tendency, the residual of two groups k value show significant 100 kyr cycles. The SPC coccolithophore calcification is sensitive to the ocean carbonate chemistry which is controlled by the upwelling induced by the East Asian Summer Monsoon in the western SCS. Thus we speculate the SPC k value residual is correlated with the East Asian Summer Monsoon wind intensity while the GEO k value residual is more related to the nutrient variations. This imply a new pattern of East Asian Summer Monsoon wind intensity variation which is different with the rain based summer monsoon dynamics.

颗石藻,钙化作用,晚第四纪