Deserts are highly sensitive to climate fluctuations and human intervention. Land degradation in deserts and surrounding areas, namely desertification, directly affects some 250 million people in the developing world and, on a larger scale, dust originating from deserts has global impacts on biogeochemistry and climate forcing. Reconstructing the environmental history of the deserts is of great importance for understanding climate change and its impacts on desertification. As the largest inland desert on Earth, the Gobi Desert is important paleoclimatologically because of its location at the northern limit of the East Asian Summer Monsoon (EASM) and close to the center of Siberian High which controls regional circulation, i.e. the East Asian Winter Monsoon (EAWM), over most of east Asia in winter. In addition, the Gobi Desert is a major source of the dust deposits that comprise the Chinese Loess Plateau, one of the most important terrestrial climate archives. In this regard, the paleoenvironmental reconstructions of the Gobi Desert are crucial for understanding regional, and even global, paleoclimate. Although the Gobi Desert landscape was formed as early as 2.6 million years (Ma) ago as a result of the evolution of Asian topography and climate during the Cenozoic, detailed knowledge of its past environment is very limited. Aeolian sands and lacustrine sediments provide some evidence of past environmental conditions in the Gobi Desert; however, these records are primarily Holocene in age because strong deflation events have removed much of the evidence from earlier intervals. This is especially the case for the East Gobi Desert. To date, the timing and magnitude of the Gobi Desert wet phases and their relationship with the EASM prior to the Holocene are still largely unresolved. Shoreline deposits from Huangqihai Lake imply a dry MIS 3 in association with the occurrence of loess, while the records obtained from Wulagai Lake indicate a warm and humid climate during MIS 3. Additionally, the Holocene climate history of the East Gobi Desert is also in dispute. Many studies suggest that the humid period may have begun 8000 years ago, However, other records suggest that the humid climate in this area already began in the early Holocene, and is highly correlated with southern Chinese speleothem isotope records. Our experience reveals that geomorphological processes also determine the hydrological conditions in this area, emphasizing the importance of geomorphological studies in paleoclimate reconstruction. All these issues require further detailed investigation. Located in the eastern part of the Asian mid-latitude desert belt, the East Gobi Desert is a relatively flat plateau bordered by mountains on the south and east. Elevations decrease gradually from 1600-2000 m in the mountainous region to 800-900 m in the northwest. Due to its location near the current northern limit of the EASM, mean annual precipitation in this area ranges from 100-400 mm with a decreasing northwestward gradient of -60 mm/100 km. Precipitation in the East Gobi Desert is characterized by a strong seasonality: summer (June-August, JJA) rainfall contributes approximately 60-70% to the annual precipitation. This combination of low precipitation and high evaporative loss produces very low runoff (<5% of the rainfall) in this area. Ephemeral streams and playas are distributed over most of the East Gobi Desert area, whereas permanent streams and lakes, albeit small and saline, are concentrated in the southeastern margin of the East Gobi Desert. In this work, we use Digital Elevation Models (DEMs) and remote sensing images to identify the presence of a mega paleodrainage network in the East Gobi Desert. Combining this work with sedimentological evidence and dating using a combination of radiocarbon, uranium series and luminescence methods, we reconstruct East Gobi Desert hydrological and climatic conditions over the last ~130 ka.

The timing of Late Quaternary high lake levels in north China has long been contentious. Studies using various proxies have yielded conflicting results regarding the extent and timing of humid periods in the region. Some studies, relying on radiocarbon dating, have suggested a dry MIS 3 and various starting points for the Holocene humid period. Other research, employing luminescence techniques, has pointed towards different interpretations. The discrepancies highlight the challenges in dating old samples using radiocarbon methods and emphasize the need for multiple dating approaches and rigorous assessment of potential biases.

This study employed a multi-faceted approach combining digital elevation models (DEMs), remote sensing imagery, sedimentological analysis, and multiple dating techniques to reconstruct the paleohydrology and climate of the East Gobi Desert over the past ~130,000 years. DEMs from various sources (GMTED2010, SRTM, ALOS World 3D) were used to identify paleolake shorelines and drainage networks, with higher resolution data providing more detailed analysis. Satellite images (Sentinel-2A, Google Earth) enhanced the identification and interpretation of geomorphic features. Detailed section analyses of sedimentary deposits provided information on past lake environments. To establish a reliable chronology, multiple dating methods were used and their limitations carefully evaluated. These methods included: radiocarbon dating of mollusk shells (Corbiculidae), uranium-series dating of mollusk shells and pedogenic carbonate coatings, and luminescence dating (quartz optically stimulated luminescence – OSL and K-feldspar post-infrared infrared stimulated luminescence – pIRIR) of sandy sediments. The radiocarbon ages are treated with caution due to potential contamination and were considered minimum ages, whereas the uranium series dating showed the necessity to evaluate the open system behavior of carbonate, with the ages of the carbonate coatings providing a more reliable constraint for the megalake formation. Luminescence dating addressed the age uncertainties inherent in the other techniques. The combination of different dating methods allowed for robust age constraints. A water balance model was developed to estimate past precipitation by equating water input (precipitation) and output (evaporation, outflow) for paleolakes at their highest stand. This model was applied, considering variations in evaporation rates and accounting for paleodischarge estimations through paleoriver channels. The model incorporated a regionally-derived empirical relationship between annual precipitation and runoff coefficient from hydrological gauges in northern China. Finally, the mollusk species presence in the lake sediment supported temperature estimation, specifically the presence of _Corbicula fluminea_, whose distribution pattern is linked to coldest month mean temperatures. The data, after careful consideration of uncertainties and limitations, was used to reconstruct the extent and duration of past lake systems, and to evaluate the relation between hydrological activity and monsoon dynamics.

The study identified a massive paleolake system in the East Gobi Desert during Marine Isotope Stage 5 (MIS 5), covering approximately 15,500 km² with a maximum depth of ~90 m. Multiple dating methods consistently dated this mega-lake system to MIS 5 (~80-100 ka). The presence of *Corbiculidae* shells in shoreline deposits indicated much warmer winter temperatures (~10 °C warmer than present) during MIS 5. A water balance model, incorporating the effect of outflow from the lake system, estimated that mean annual precipitation during MIS 5 was 120-150% higher than present, implying a northward shift of the humid climate zone by 800-1000 km. This significant increase in precipitation during MIS 5 is attributed to a strengthened East Asian Summer Monsoon (EASM). A second, smaller, wet phase occurred during the mid-Holocene (~6.7 ka) in the southern basin of the study area, with a lake level significantly lower than the MIS 5 highstand. The analysis of the lake’s extent during MIS5 and mid-Holocene demonstrated that during MIS 5, the paleolake covered an area of ~15,500 km². The study further linked the humid climate of MIS 5 to a dustier MIS 4 across East Asia and the North Pacific. The drying up of the extensive lake systems after MIS 5, coupled with intensified East Asian Winter Monsoon (EAWM) conditions, is proposed as a driver of the increased dust flux during MIS 4. The results suggest a stronger EASM during MIS 5 and a weaker one during MIS 3, challenging previous interpretations based solely on south China cave records. It also suggests a significant and underappreciated longitudinal precipitation trend across East Asia during the Holocene and MIS 5 that isn't fully captured in south China cave records.

The findings of this study address the long-standing debate regarding the timing and magnitude of wet phases in East Asian deserts. By integrating multiple proxies and dating techniques, the research provides robust evidence for a significant expansion of the EASM during MIS 5, leading to the formation of a vast paleolake system in the East Gobi Desert. The correlation between the humid MIS 5 and a dustier MIS 4 suggests a complex interplay between monsoon intensity, lake desiccation, and dust mobilization. The discrepancies between the study's findings and those derived from south China cave records highlight the need for a more integrated approach in paleoclimate reconstruction, acknowledging the longitudinal precipitation gradients across East Asia. The identification of warmer winters during MIS 5 challenges existing paleoclimate models and calls for further investigations into the mechanisms driving winter temperature variations in this region. The study’s findings underscore the importance of incorporating geomorphological evidence and various dating techniques to achieve more comprehensive understandings of past climate variability.

This study provides a detailed reconstruction of the East Gobi Desert paleohydrology over the past ~130 ka, identifying two significant humid periods during MIS 5 and the mid-Holocene. The results highlight the powerful influence of the EASM during MIS 5, leading to extensive lake formation and a northward expansion of the humid climate zone. The findings challenge previous interpretations of East Asian monsoon dynamics, emphasizing the need for more comprehensive regional records. Future research could focus on refining paleodischarge estimations, investigating the provenance of dust deposited in surrounding areas, and modeling the impact of winter temperature changes on atmospheric circulation patterns. This would further help refine our understanding of past climate shifts and their broader implications.

The study acknowledges several limitations. The radiocarbon ages are considered minimum ages due to potential contamination, while uranium-series dating was affected by open-system behavior in some samples. Luminescence dating, while providing valuable age constraints, relies on assumptions about the sediment's depositional history. The paleoprecipitation estimations from the water balance model rely on the accuracy of the empirically derived runoff coefficient and assumptions about lake evaporation rates. Additionally, the lack of precise provenance data limits the ability to quantify the relative contributions of different dust sources to the increased dust flux during MIS 4. Further, the exact timing of paleoriver incision remains uncertain.