Magnetic mineral dissolution front delimited by late Holocene sediment accumulation acceleration in the inner shelf, northern South China Sea

Inner shelf sediment properties are sensitive indicators of Holocene environmental changes; however, magnetic records can be altered by reductive dissolution. To refine our understanding of magnetic mineral dissolution, we conducted detailed analyses of three sediment cores from the inner shelf of the northern South China Sea. AMS 14 C dating, grain-size, magnetic parameters, mineral composition, organic carbon, and sulfur content were examined. The cores, composed uniformly of clayey silt and spanning the past 4–6 ka, were divided into three zones: (1) a suboxic surface layer (40–88 cm thick), (2) an intermediate zone with moderate magnetic properties, and (3) a basal zone characterized by intense magnetic mineral dissolution. Identified minerals include magnetite, hematite, and iron-sulfide phases such as pyrite. The depth of the suboxic–sulfate boundary (Zones 1–2) was inversely correlated with sedimentation rate and water depth. The magnetic dissolution front (Zones 2–3 boundary) coincided with a sharp increase in sedimentation over the past 1–2 ka, likely linked to intensified human activity. These results suggest that anthropogenic environmental changes may have influenced magnetic mineral reductive dissolution, warranting further investigation. • Early diagenesis was detected in 3 cores from the northern South China Sea inner shelf. • Strong magnetic mineral dissolution occurred at boundary of accumulation transfer zone. • Human-promoted sediment input may have affected the dissolution of magnetic minerals.