Quaternary

The evolution of multidecadal climate variability in the Asian monsoon region across cold-to-warm transitions over the past two millennia remains poorly constrained. Here, we present high-resolution multi-proxy records (δ¹³C, δ¹⁸O, Mg/Ca, Sr/Ca, and Ba/Ca) from stalagmite RY2 in Riyue Cave, southwestern China, spanning 673–1307 CE, to investigate multidecadal climate variability and its driving mechanisms from the Dark Ages Cold Period (DACP) to the Medieval Warm Period (MWP). Our results indicate that RY2 δ¹³C mainly reflects temperature-related regional ecosystem changes under the humid monsoonal setting, as supported by significant correlations with independent temperature reconstructions. Furthermore, the RY2 multi-proxy records indicate reduced multidecadal variability from the DACP to the MWP. This decline is statistically robust in the temperature-sensitive δ¹³C record and in the three trace-element records, whereas the corresponding change in δ¹⁸O is weaker and not statistically significant. The observed pattern is consistent with a possible role for enhanced solar variability and greater instability in North Atlantic Ocean sea-ice conditions during the DACP, although the present evidence primarily supports temporal correspondence, and these factors’ relative contributions remain to be quantified.

The Younger Dryas (YD) terminated the last glaciation and initiated the Holocene, which was accompanied by widespread glacial advances. Traditional scaling models, production rates, and outlier screening approaches for ¹⁰Be exposure dating often yield inconsistent formation ages for the same moraine, hindering a comprehensive understanding of spatiotemporal patterns and climatic controls of YD glaciation across the Tibetan Plateau. In this study, we reprocessed ¹⁰Be exposure ages using the Probabilistic Cosmogenic Age Analysis Tool 2.2 (P-CAAT) to constrain YD moraine chronologies. Three glacial events were dated to 12.5 ka, 11.9 ka, and 11.5 ka. Glacier-climate simulations showcased cold dry conditions in the monsoon domain and cold-wet conditions in the westerly domain during the YD. The modelled temperature reductions matched global climatic records. Glacial advances were primarily forced by cooling in monsoon areas, whereas joint cooling and increased precipitation dominated in westerly regions. This study clarifies the temporal characteristics and driving mechanisms of YD glaciation on the plateau, though additional dating information is required for further verification.

Quartz purity is essential for reliable optically stimulated luminescence (OSL) dating, yet the mineralogical evolution of sediment samples during extraction is rarely documented at each preparation stage. This study uses scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) to characterise two loess samples from the Urluia section, Dobrogea, Romania, across sixteen successive stages of a standard OSL quartz extraction protocol. Four compositional indices—the Quartz Purity Index (QPI), Feldspar Contamination Index (FCI), Heavy Mineral Index (HMI), and Carbonate Index (CI)—are introduced to quantify purification efficiency. Each preparation stage played a different role: HCl treatment primarily removed carbonates, grain-size separation and density fractionation reduced heavy minerals by ~99%, and feldspar removal resulted from the combined effects of density separation and HF etching. Despite identical protocols, two samples collected from stratigraphically adjacent positions showed markedly different HF etching efficiencies, reaching ~94% and ~66% quartz purity, respectively. However, luminescence measurements showed similarly weak feldspar signals in both samples, with intensities substantially lower than the quartz OSL signal. These results demonstrate that purification efficiency cannot be assumed to be uniform across loess samples in Romania and highlight SEM-EDS as a practical quality-control tool for OSL sample preparation.