Characteristics of palaeosalinity and palaeoredox records in sediment from Dali Lake: Climate change in North China from 0 to 2100 cal BP

To understand the salinity, redox characteristics, and climatology of Dali Lake during the late Holocene, we analysed trace element records from a high-resolution sediment core (DL-1), including Al, Mn, Zn, Mo, Pb, Fe, Sr, and Ba. The core was dated to 2100 cal BP based on accelerator mass spectrometry (AMS) 14C dating combined with the constant rate of supply (CRS) model. We identified five palaeoclimatic stages based on the down-core trace elemental characteristics. From ca. 2100 to 1650 cal BP (Stage Ⅰ), Mn-MAR (mass accumulation rates) and Fe-MAR showed no correlations with Mo-MAR, suggesting that anaerobic conditions limited the adsorption of Mo onto Mn–Fe oxides. From ca. 1650 to 1050 cal BP (Stage Ⅱ), we identified a weakened aerobic environment, coinciding with the Dark Ages Cold Period due to a decrease in the organic matter (OM), nutrients, Fe-MAR, and Zn-MAR, which inhibited Mo deposition. Salinity (Sr/Ba) did not influence the trace elemental fluxes, OM, or nutrients throughout Stages I and II. We identified aerobic conditions during Stage Ⅲ (between ca. 1050 and 650 cal BP), coinciding with the Medieval Warm Period, with observed lower salinity that facilitated Al-MAR, Mn-MAR, and Pb-MAR deposition. During the Little Ice Age (between ca. 650 and 30 cal BP; Stage Ⅳ), Mn-MAR, Zn-MAR, and Fe-MAR showed no correlation with Mo-MAR, implying anaerobic conditions. We also identified high salinity and OM concentrations that facilitated trace element deposition. Over the past 95 years (Stage V), high salinity levels have produced the deposition of Al-MAR, Mn-MAR, Zn-MAR, and Fe-MAR. However, the redox conditions in the lake sediment are difficult to interpret due to anthropogenic influences on trace elemental fluxes. We identified a salinity periodicity (Sr/Ba) of 100–150 years and a redox periodicity (Mo-MAR) of 100–260 years using the wavelet power spectrum. Our results indicate a gradual weakening of the East Asian summer monsoon, which may be controlled by insolation in the Dali Lake basin.