Assessing terrigenous contributions to South China Sea (SCS) deep-sea sediments provides valuable insights into ocean–continent interactions and marine biogenic carbon preservation. This study investigates changes in terrigenous input to the northeast SCS over the last 230 kyr using physical and geochemical data from IODP Expedition 349 Hole U1432C (3829 m depth), retrieved by IODP Expedition 349. Terrigenous contributions were evaluated using natural gamma radiation (NGR), and sediment elemental ratios (Ti/Ca and Al/K). A principal component analysis (PCA) and Pearson’s correlation matrix were applied to analyze sediment composition. PCA revealed that terrigenous supply (PC1, PC3) and marine biogenic carbon (PC2) drive geochemical variations in Hole U1432C. Increased NGR, PC1, PC3 scores, Ti/Ca, and Al/K ratios, indicate heightened terrigenous input during interglacial MIS 5, likely caused by stronger East Asian Summer Monsoon (EASM) activity and enhanced physical weathering. Terrigenous dilution reduced marine biogenic carbon content during interglacial periods, while higher contributions of marine carbon were observed during glacials, particularly from MIS 5 to MIS 1. These results highlight the dynamics of the EASM and shifting terrigenous sediment sources as key drivers of SCS sedimentation over the past 230 kyr. Moreover, these findings highlight the role of terrigenous supply in diluting the marine biogenic carbon contribution to the deep ocean.