Late Quaternary coccolith records in the South China Sea and East Asian monsoon dynamics

Coccolithophorid assemblages over the past 260 ka were analyzed in three sediment cores (MD05-2904, MD05-2897 and MD05-2901) from the northern, southern and western South China Sea (SCS), respectively. Past changes in the nutricline depth and primary productivity (PP) were reconstructed using the relative abundance of the coccolithophore Florisphaera profunda. Our records show that the nutricline in the northern and the southern SCS both shoaled during glacial periods but deepened during interglacial periods. However, the nutricline depth and PP in the western SCS did not reveal any significant changes paced with glacial-interglacial cycles. We suggested that the East Asian Winter monsoon dominates the nutricline and PP variations in the northern and southern SCS. In the western SCS, the winter-monsoon signal in the reconstructed coccolith records might have been muted by the influence of the local summer upwelling. The relative abundance of F. profunda show significant Milankovitch spectrum peaks at the three sites, and is out of phase with the global common feature at the precessional bands. Through Empirical Orthogonal Function (EOF) analyses on F. profunda records of the SCS and the Sulu Sea, two significant EOF modes are isolated. EOF-1 reflected glacial-interglacial variations which might be a response to the dynamics of the East Asian Winter monsoon. EOF-2 shows both strong ~ 20 kyr precession and ~ 40 kyr obliquity cycles and probably related to the East Asian Summer monsoon evolution.