Buried ice-wedge pseudomorphs as indicators of Younger Dryas climate-related lake evolution, Dali Lake, Inner Mongolia

Ice wedges / pseudomorphs (IWPs) are key indicators of cold-climate (periglacial) frozen ground conditions. Their occurrence within the sedimentary sequences of lacustrine landforms can provide important evidence about palaeoenvironmental and palaeoclimatic change. However, research using lake sediments in a geomorphological context to investigate climate change is limited. Here, we use newly discovered IWPs developed within lake sediment sequences to explore climate-related lake-level fluctuations in the Dali Lake region, a key area of the East Asian summer monsoon (EASM) system that drives Quaternary hydroclimate variability across East Asia. The IWPs penetrate down through clay-silt lake sediments and are overlain by coarser-fossiliferous, and finer-diatomaceous lake sediments. This configuration suggests IWP formation occurred within an area transitioning sequentially between subaqueous, subaerially exposed, and resubmerged lake margin setting. We employ the optically stimulated luminescence (OSL) and AMS radiocarbon dating methods to constrain ice-wedge activity timing. Results reveal ice wedge formation between 12.84 and 11.31 ka, corresponding to the globally significant Younger Dryas (YD) cold-climate event. The colder climate since 12.84 ka has led to a marked lake level decline, exposing shoreline areas, which subsequently became frozen, resulting in fissure development and ice infilling. Subsequently, the lake level increased, resulting in a minor highstand, with fossiliferous lake sediment accumulation over the ice wedges during 12.50 ka to 11.94 cal kyr BP. From 11.94 cal kyr BP to 11.31 ka, the lake level declined again, with concomitant ice wedge development. These three lake-level changes and their IWP characteristics reflect regional YD hydroclimatic variability. Wider research using high-resolution multi-proxy analysis of lake sediment cores suggests sustained cold-dry climate conditions during the YD. Our results, using the lake sediment-landform sequence, also suggests a cold climate (similar to 8.2 degrees C colder than today) but one that fluctuated between dry-humid-dry hydrological patterns during the YD. This study highlights the potential for using IWP affected lake sediment-landform sequences to improve understanding of landscape responses to YD climate variability in the EASM affected region.