Carbonate-rich sequences in the deep sea of the eastern South China Sea subbasin (IODP Hole U1431D) during the last 600 kyr

Abstract

Here, we examined changes in carbonate preservation in a deep-sea record (Hole U1431D, 4240 m water depth) retrieved from the South China Sea (SCS) during the International Ocean Discovery Program (IODP) Expedition 349. To evaluate these changes, we applied a micropaleontological and geochemical multiproxy approach including, planktonic foraminifera (PF) total abundance, fragmentation (FI%) and dissolution (FDX) indexes, and total organic carbon (TOC). The results of this study showed that during the last 600 kyr, Hole U1431D site has been under the effect of carbonate dissolution associated with the deepening of the lysocline and the Calcite Compensation Depth. Nonetheless, during MIS 8 and MIS 7, there was a significant increase in PF total abundance and TOC content. The low PF total abundance found in some intervals resulted in an underestimation of the FI% and FDX indexes. Although high PF total abundance events occur at Hole U1431D turbidite sequences, these are also interpreted in the context of higher primary productivity (PP) in the central SCS. High TOC contents from MIS 10 to MIS 6 were associated with the effects of enhanced PP during the Mid-Brunhes Dissolution Interval as well as the dynamics of the East Asian Monsoon (EAM). During MIS 8 and 7, increased abundances of PF and TOC contents may have been related to enhanced PP promoted by the seasonal EAM. Our data suggest that enhanced PP associated with the occurrence of turbidite currents at the East SCS subbasin allowed the preservation of PF at Hole U1431D.