Variation of organic carbon flux in the northeastern South China Sea since the last glacial maximum and the driving mechanism

To investigate the variations of organic carbon flux and their driving mechanisms since the Last Glacial Maximum (LGM), we examined The variation of total organic carbon (TOC), total nitrogen (TN), and stable organic carbon isotope (δ¹³C_TOC) in core MD18-3569 collected offshore of southwestern Taiwan in the northeastern part of the South China Sea. Results indicate that the values of TOC and TN ranged from 0.13% to 0.40% and 0.017% to 0.061%, which exhibit a characteristic pattern of higher values during glacial periods and lower values during the Holocene. The values of C/N ratio and δ¹³C_TOC ranged from 5.90 to 8.58 and −25.15‰～−22.61‰, which indicate a mixed marine-terrigenous source for organic carbon at MD18-3569. Marine organic carbon mainly originates from marine primary producers, primarily marine algae, while terrigenous organic carbon primarily comes from rivers in southwestern Taiwan. According to the marine-terrigenous end-member model calculations, the values of marine organic carbon flux and terrigenous organic carbon flux ranged 0.01 ～ 0.12 g·cm⁻²·ka⁻¹ and 0.05 ～ 0.21 g·cm⁻²·ka⁻¹, respectively. The marine organic flux had generally been decreased since the LGM. The high marine organic carbon flux during the glacial period might be due to stronger East Asian winter monsoon that enhanced the vertical mixing of seawater, which increased the nutrient content and consequently the marine primary productivity in the upper seawater. In contrast, terrigenous organic carbon flux showed an increasing trend since the LGM duo likely to the impact of precipitation from the East Asian summer monsoon on the rivers in the southwestern Taiwan. Sea level changes since the LGM also played a certain role in this process by the shifting of river mouth. Therefore, the East Asian monsoon system resulted in significant influence on the burial of organic carbon in the northeastern South China Sea since the LGM.