Differences in Late Quaternary primary productivity between the western tropical Pacific and the South China Sea: Evidence from coccoliths

Abstract

Changes in Late Quaternary oceanic primary productivity in the western tropical Pacific were reconstructed using coccolith counts from the improved SYRACO system in piston core MD01-2386 retrieved from the Halmahera Sea near northwest New Guinea. The calculated primary productivity exhibits cycles on obliquity and precession timescales over the last 192ka. There are marked differences between primary productivity records from the western tropical Pacific and the South China Sea (SCS), with the former being dominated by precession, and the latter showing all three Milankovitch cycles (eccentricity, obliquity and precession). Empirical Orthogonal Function (EOF) analyses reveal two significant EOF modes in the western tropical Pacific and SCS records. EOF-1 accounts for 38% of the total variance and exhibits obvious precessional cycles corresponding to Northern Hemisphere summer insolation, while EOF-2 accounts for 22% of the total variance and exhibits strong 41-kyr periodicity, suggesting different biological responses to hydroclimate changes in the two regions. A more complex hydroclimate regime influenced by the East Asian monsoon and the large contrast in regional topography and circulation during glacial cycles are considered to be the primary drivers of the stronger temporal variability in productivity in the SCS compared to the relatively stable western tropical Pacific.