Magnetic characteristics of sediments in the northern Yangtze River delta since MIS3 and their responses to palaeoenvironmental changes

The Yangtze River Delta (YRD), located at the confluence of terrestrial and marine environments, is influenced by various hydrodynamic factors, including oceanic, fluvial, and tidal processes, which together create a distinctive sedimentary environment. This research examined the sediment magnetic minerals of the upper 0–61 m of the core YZ07 in the northern YRD. Combined with optically stimulated luminescence (OSL) dating, various climatic and environmental indicators, the mechanisms about sedimentary magnetic parameters responding to palaeoenvironmental changes were discussed. The results indicate that the dominant magnetic minerals in the core YZ07 sediments were coarse-grained pseudo-single domain (PSD) and multidomain (MD) magnetite, with minor amounts of hematite. Between 53.0 and 37.5 ka B.P., χ and SIRM values were high, while χ_ARM/χ and χ_ARM/SIRM values were low. These indicated a relatively warm and humid climate characterized by higher precipitation and stronger hydrodynamic conditions in the Yangtze River basin. The concentration of magnetic minerals decreased and grain sizes became finer from 37.5 to 30.7 ka B.P., suggesting a decline in temperature and precipitation. During the Marine Isotope Stage 2 (MIS2), the values of χ and SIRM declined, whereas the values of χ_ARM/χ and χ_ARM/SIRM increased, reflecting a cooler climate with reduced precipitation and weakened hydrodynamic conditions. The sediments in the Holocene showed higher concentrations of magnetic minerals and coarser grain sizes, indicating a warm and humid climate with strong hydrodynamic conditions. Conversely, among the intervals of 8.4 to 7.5 ka B.P., 4.3 to 3.4 ka B.P., and 1.7 to 1.3 ka B.P., the contents of magnetic minerals decreased and the grain sizes became finer, corresponding to cold and dry climatic events within the Holocene period. Magnetic parameters of core YZ07 show a strong correlation with global and regional environmental changes, suggesting that climate changes result in alterations to the hydrodynamic conditions of the Yangtze River.