Aufeis is a seasonal ice accumulation formed by successive freezing of groundwater or surface-water overflow on land surfaces, river ice or lake ice during winter. It is widespread across cold regions and plays important roles in hydrology, geomorphology, ecosystems, and infrastructure stability, yet remains underrepresented in regional and global cryospheric assessments. This review synthesizes recent advances in aufeis research, focusing on spatiotemporal distribution, formation mechanisms, seasonal dynamics, environmental functions, engineering impacts, and mitigation strategies, while identifying major knowledge gaps and future research priorities. Current evidence suggests that aufeis extent has generally declined in many cold-region landscapes over recent decades, although large uncertainties persist in forested, mountainous, and data-sparse regions, particularly across Asia. Under continued climate warming and hydroclimatic intensification, aufeis is likely to become smaller, more fragmented, and less spatially continuous. However, its response is not uniformly negative: permafrost degradation may locally enhance groundwater recharge, talik development, and winter baseflow, thereby promoting aufeis formation in some settings. This dual response highlights the strong dependence of aufeis dynamics on local hydrogeological structure, permafrost conditions, snow regime, and surface-subsurface connectivity. Beyond its geomorphic expression, aufeis can function as an important seasonal water reservoir, contributing substantially to spring and early-summer runoff and, in some basins, rivaling or exceeding the hydrological contribution of nearby small glaciers. These hydrological functions are critical for sustaining cold-region ecosystems, regulating streamflow seasonality, and buffering water scarcity during early thaw periods. At the same time, aufeis poses persistent and in some cases growing risks to roads, railways, pipelines, and other linear infrastructure, prompting a shift from conventional passive control measures toward integrated, process-informed, resilience-based mitigation. Aufeis-related landforms, sedimentary records, and geochemical signatures also provide valuable archives for reconstructing Quaternary hydrogeological and periglacial environments. A process-based, interdisciplinary understanding of aufeis is therefore essential for predicting its response to climate change, improving cold-region water resource assessment, interpreting paleoenvironmental records, and supporting the design, maintenance, and adaptation of resilient infrastructure in a warming cryosphere.

Understanding the responses of wildfires to long-term climate variability is critical for improving fire management strategies and maintaining ecological stability. However, the spatial heterogeneity and drivers of wildfires in the East Asian monsoon (EAM) region on orbital timescales remain poorly constrained. In this study, wildfire dynamics across the last five glacial-interglacial cycles were determined based on a similar to 480 kyr wildfire history reconstructed from black carbon (BC) records in the Huangshan loess-paleosol sequence in northeastern China. The results revealed substantial glacial-interglacial cycles in northeastern China, with more intense fires during interglacials than glacials. Comparative analysis with other wildfire records revealed notable spatial heterogeneity of wildfires across the EAM region on the glacial-interglacial timescale. Wildfires in the eastern East Asian monsoon (EEAM) region were more active during interglacials, likely due to higher temperatures and greater biomass availability. Conversely, those in the western East Asian monsoon (WEAM) region were more frequent during glacials because of fuel desiccation caused by reduced precipitation. Overall, the large-scale spatial precipitation pattern, which gradually decreased from southeast to northwest in the EAM region, may serve as the core driver of wildfire spatial heterogeneity. Under future global warming, the EEAM region will likely face elevated wildfire risks and should be prioritized for fire prevention.

The Pliocene-Pleistocene transition (PPT), marking the intensification of Northern Hemisphere glaciation, drove significant global and regional vegetation shifts. However, ecological responses to this transition in Northeast China remain poorly constrained due to a scarcity of high-resolution palaeovegetation records. Here, we reconstruct vegetation dynamics during the PPT (3.204-2.380 Ma) using pollen and charcoal assemblages from the HL borehole, combined with quantitative estimates from the REVEALS model. Generalized Additive Models (GAM) and Structural Equation Modeling (SEM) were applied to disentangle the relationships between vegetation and environmental drivers. Our results reveal four distinct stages of vegetation evolution: (1) 3.204-2.894 Ma: Coniferous taxa (Pinus, Picea, and Tsuga) dominated a relatively stable, high-diversity forest ecosystem. (2) 2.894-2.736 Ma: Total woody cover decreased, coinciding with enhanced vegetation turnover and increased diversity. (3) 2.736-2.491 Ma: Woody cover declined further, resulting in mixed coniferous-broadleaved forests with reduced diversity. (4) 2.491-2.380 Ma: Grassland cover expanded significantly while thermophilous forest components largely retreated, leading to a marked decline in overall diversity. SEM analyses indicate that broadleaved forest cover was primarily driven by atmospheric pCO(2), whereas coniferous forest cover was more sensitive to fire activity. The expansion of open grassland cover was jointly controlled by fire regimes and the summer monsoon index (SMI). Ultimately, a critical ecological threshold was crossed at similar to 2.491 Ma, when vegetation abruptly shifted from mixed forests to open steppe environments. This transition reflects an amplified vegetation response to cooler and drier hydroclimatic conditions, coupled with intensified fire activity during the early Pleistocene.

The total organic carbon (TOC) content in lake sediments is an effective archive indicating past climate changes. However, the resolution of the TOC record has generally been limited by factors such as subsampling intervals, hampering further comprehension of past climate change. Recently, hyperspectral imaging technology has been increasingly employed to scan lake sediment cores, presenting new opportunities to reconstruct high-resolution sequences, but the reconstruction of long-term high-resolution TOC records using hyperspectral imaging and the climate implications have not been well studied. In this study, we scanned sedimentary cores from Wudalianchi Crater Lake in northeast China with a spatial resolution of 400 × 400 μm, utilizing visible and near-infrared (VNIR) hyperspectral imaging technology. Then, a partial least-squares regression (PLSR) model was constructed by comparing eight different preprocessing methods and optimally selecting the best spectral subset combined with a genetic algorithm (GA). Our analysis demonstrates that the PLSR model, constructed using 62 relevant bands selected by the Savitzky–Golay second derivative (D2) preprocessing method and GA, was the most reliable, with the validation set’s R-value reaching a high of 0.91 and RMSE as low as 1.18%. Notably, the spectral range of 656–669 nm showed a strong positive correlation with measured TOC, indicating its sensitivity for TOC estimation. Given this advantage, we reconstructed the TOC records of sediments from the Wudalianchi Crater Lake during the 38–13 ka BP period, which exhibited significant millennial-scale fluctuation events. These corresponded well with the millennial-scale events in pollen and TOC from Lake Sihailongwan, δ18O records of Greenland ice cores, and δ18O records from Asian stalagmites. Thus, the combination of hyperspectral imaging and the PLSR model is effective in reconstructing high-resolution TOC changes in lake sediments, which is essential for understanding climate change as well as carbon burial in lakes.

Recent changes in land use in the Mollisol region of the Sanjiang Plain have significantly impacted speciation and bioavailability of selenium (Se) in soils. This study examines Se species and distribution across various land use types, focusing on the interactions between iron oxides and organic matter in Se migration and transformation. The total Se content in woodland, dryland, and paddy soils is 0.79 mg/kg, 0.80 mg/kg, and 0.82 mg/kg, respectively, showing a uniform distribution. Soil organic carbon (SOC) is positively correlated with total Se, with complex effects on Se species. In paddy soils, SOC is positively associated with organic-bound Se and residual Se; Se content decreases with increasing soil depth in both profiles, following a typical surface accumulation pattern. Additionally, water management in paddy fields plays a critical role: prolonged water retention at the surface promotes Se enrichment in the topsoil and enhances dissolved Se leaching from deeper layers. This research indicated that coupling iron oxides and organic matter is crucial in Se fixation, particularly in paddy soils. Bioaccumulation factor (BCF) analysis shows a significant correlation between Se content in crops and soil Eh and pH, with higher Eh enhancing Se uptake. This study highlights the influence of land use and soil properties on Se bioavailability.

The Sanjiang Plain, a crucial cold-region agricultural hub in China, hinges on groundwater security for ecological stability and human well-being, necessitating comprehensive water quality assessment. This study analyzed 150 groundwater samples, measuring basic parameters and ion concentrations to uncover three significant findings: secondly, Multi-layer weighted principal component analysis (MLWPCA) is superior to traditional principal component analysis (PCA) in cold agricultural regions. Specifically, while providing an overall evaluation, the use of subsets allows for a more detailed evaluation and calculation of groundwater quality, thereby making the evaluation of groundwater quality more reasonable. Finally, while most groundwater remains suitable for irrigation and drinking, targeted management strategies are required to mitigate nitrogen pollution. The study’s findings and the innovative MLWPCA approach offer actionable insights for sustainable groundwater management and agricultural development in the Sanjiang Plain and similar cold regions.

Chronology plays a pivotal role in paleoenvironmental and paleoclimatic reconstructions. Radiocarbon dating and optically stimulated luminescence (OSL) dating are two commonly used dating methods for determining the age of eolian deposits on the northeastern Tibetan Plateau (NETP). However, there is currently a lack of detailed comparison between these two dating methods for eolian deposits on the NETP since 14 kyr (thousand years). Here we present closely spaced radiocarbon ages of total organic carbon (TOC) from two typical eolian deposit sections on the NETP. Moreover, these radiocarbon ages were compared with OSL ages. In the QJH section, located in the Qinghai Lake area, radiocarbon ages are found to be up to 2171 yrs. (years) younger than the corresponding OSL ages, specifically below a depth of 40 cm. This suggests that the radiocarbon dating material was probably contaminated by new carbon derived from modern plant roots. Interestingly, in the YM section, radiocarbon ages are up to 1318 yrs. older than the corresponding OSL ages, indicating a potential influence of old carbon on the radiocarbon dating material. Consequently, when determining the age of eolian deposits on the NETP, great caution should be exercised when relying on radiocarbon ages of TOC, especially in the absence of cross-checking methods.

The climate change in the Qaidam Basin has significant impacts on local humans and ecological environment. However, the humidity variation and relationship between climate factors in the Qaidam Basin remain insufficient. Here we study the modern climate change in the Qaidam Basin. The mean annual temperature in the Qaidam Basin has increased rapidly by 0.5 °C/10a between 1959 and 2022, exhibiting cycles of 9.1 a and 3.2 a. Concurrently, the pattern of precipitation variations has displayed an upward trend, with a rate of increase amounting to 9.2 mm/10a and a cycle of 2.5 a. The Qaidam Basin has witnessed a considerable increase in temperature since 1977, as indicated by the Mann–Kendall mutation test. Within the Qaidam Basin, the mutation point at which precipitation transitioned from a lesser amount to a more volume occurred in 2001. Furthermore, a reduction in the variation of evaporation was observed between 1959 and 2003, possibly attributed to decreased sunshine and wind speed within the basin. The moist coefficient (precipitation/evaporation) and absolute humidity serve as direct indicators of the level of humidity in the environment. The moist coefficient has displayed an upward trend, accompanied by a corresponding increase in absolute humidity. The lake area and vegetation coverage are indirect indicators that reflect the level of humidity in the environment. In the Qaidam Basin, the lakes have expanded in surface area and there has been a noticeable increase in vegetation coverage. Collectively, these indicators unambiguously show that the Qaidam Basin is undergoing a process of increased moisture levels. Thus, it can be deduced that the modern Qaidam Basin is both experiencing warming and becoming wet.

Known as the “Holocene temperature conundrum”, controversy remains between paleoclimate reconstructions indicating cooling during the late-Holocene versus model simulations indicating warming. Here, we present a composite Holocene winter temperature index record derived from East Asian winter monsoon (EAWM) reconstructions. This new temperature index record documents a thermal maximum occurring during the mid-Holocene, followed by a cooling trend. Along with other Holocene winter temperature reconstructions, these findings collectively indicate a cooling trend during the late-Holocene, consistent with global annual average temperature reconstructions. Notably, our composite dust records and dust sensitivity simulations identified enhanced global aeolian dust, which has been overlooked in previous model simulations, as a likely driver of the cooling trend throughout the mid- to late-Holocene. Our new evidence does not support the current seasonal bias explanation of the Holocene temperature controversy, but instead suggests potential mechanisms that could help explain the differences between temperatures inferred from models and paleo-reconstructions in the past.

The 4.2 ka event is an important climatic event of the Holocene that is expected to considerably influence the development of human civilizations. However, the forcing mechanism of the 4.2 ka event remains unclear, with current evidence being divided between high-latitude and low-latitude forcings. The Asian climate system contains strong summer and winter monsoon circulations, and thus the region is ideal for studying high- and lowlatitude climate forcings on 4.2 ka event. In this study, we present a high-resolution pollen record of the past 5000 years from Wudalianchi Crater Lake in northeastern China in the East Asian monsoon region. An evident decrease in broadleaf trees occurred during the 4.2 ka event, suggesting a decrease in summer monsoon rainfall. Well-dated high-resolution pollen, stalagmite 818O, and winter monsoon records were collected to study the possible transportation of high- and low-latitude signals. Most of the pollen records showed significant changes during the 4.2 ka event, while no apparent change was found in winter monsoon records. Meanwhile, more obvious changes in stalagmite 818O records were observed in lower- rather than the higher-latitude regions around 4.2 ka. Our results suggest that the signal of the 4.2 ka event might be transported by low-latitude processes, thus corresponding to a low-latitude forcing.

Previous studies of the carbon reservoir effect in lake sediments and its influencing factors have focused mainly on the Holocene; however, changes in carbon reservoir effect and its driving mechanisms before the Holocene remain poorly understood. In this study, we produced a time series of changes in the bulk sediment carbon age offset (Δt) from Wudalianchi Tianchi Lake, northeastern (NE) China. The results showed that changes in Δt largely corresponded to temperature and precipitation variations during the Last Glacial and Holocene. During relatively warm-humid periods, the low or zero Δt mainly resulted from increases in vegetation/phytomass which caused the increased relative contribution of contemporaneous carbon to the sedimentary total organic carbon. In contrast, the higher Δt during the Last Glacial Maximum was related to increases in old carbon from the surrounding catchment and aeolian dust, and thus to increased relative contribution of old carbon to the sedimentary total organic carbon. This climate-Δt relationship may also have operated during stadials, interstadials and Heinrich events.

Numerical simulations utilizing OpenGeoSys have been conducted on a deep coaxial borehole heat exchanger situated in the Songliao Basin. The findings reveal that the outlet temperature exhibits a downward trend as circulation flow increases, while it rises with an increase in inlet temperature. Additionally, the heat transfer power escalates with higher flow rates but diminishes as inlet temperature rises. Notably, the long-term operation results in a reduction of outlet temperature and heat transfer power. After 30 years, the decline of them is approximately 0.3 degrees C and 8 kW under current situation. Furthermore, long-term operation induces a decrease in formation temperature, predominantly around the vicinity of well, where the maximum temperature decline is nearly 30 degrees C. The reduction in formation temperature is directly proportional to the increase in flow rate and inversely proportional to inlet temperature. Within the depth range of well, the maximum influence radius expands in correlation with both the depth and duration of mining, while remaining relatively stable with variations in flow rate and inlet temperature. Following three decades of extraction, the influence radius is approximately 95m. The results provide vital scientific insights for the retrofitting of abandoned wells in Northeast China into geothermal heat exchange wells for building heating purposes.

The Liupan Mountains, one of the important mountain ranges in western China, are located on the boundary between the northeastern Tibetan Plateau and the Ordos Block. The uplift history of the Liupan Mountains remains controversial. Loess deposits are good tracers of regional tectonic and geomorphic changes, because loess is sensitive to erosion and the formation and preservation of loess requires relatively flat highlands and relatively stable tectonic environments. We investigated the distribution of Neogene loess deposits on the western piedmont of the Liupan Mountains and examined a near-continuous loess section (Nanping section) on the piedmont alluvial highlands. Correlation of magnetic susceptibility stratigraphy with the QA-I Miocene loess sequence dates this 56-m section covering the interval from 8.1 to 6.2 Ma. The lower boundary age of this section, together with previously reported Zhuanglang red clay (sand-gravel layers with intercalated loess during 9–8 Ma and near-continuous loess during 8–4.8 Ma) and Chaona red clay ( 8.1–2.58 Ma), indicates that the Liupan Mountains were uplifted in the late Miocene ( 9–8 Ma) and basically formed by 8 Ma, attesting to no intense mountain building since that time. In addition, based on the information from the Zhuanglang core and the QA-I section, we infer that sizable parts of the Liupan Mountains were uplifted during the late Oligocene–early Miocene and did not experience intense uplift during 22–9 Ma.

Lacustrine sediments are ideal archives for investigation of the evolution of climate and environment. During the early-mid Pleistocene, there was a huge lake (Songnen paleo-lake) in the Northeast China Plain. The evolutionary history and mechanism of this ancient lake need to be further studied with more boreholes. Here we present the results of "Al/"Be and paleomagnetic geochronology, magnetic susceptibility stratigraphy and rock magnetism obtained from the HL core (A borehole in Dumeng county of the Northeast China Plain). The boundary between the lacustrine sediments of Lingzi Formation and Lindian Formation was dated to be about 900 ka. The magnetic susceptibility of Lindian Formation was evidently higher than that of Lingzi Formation, and hysteresis loops and %-T curves of these representative samples show that the contribution of paramagnetic minerals and high coercivity weak magnetic minerals of Lingzi Formation was relatively large. The increase of magnetic susceptibility may be related to the decrease of lake level, the enhancement of hydrodynamic force, the increase of strong magnetic minerals entering the lake or the change of redox conditions, resulting in the formation of strong magnetic iron sulfide. At about 900 ka, the Songnen paleo-lake shrank, which may be related to the less East Asian summer monsoon precipitation. The weakening of the Atlantic meridional overturning circulation (AMOC) and the southward movement of the Intertropical Convergence Zone (ITCZ) in the tropical Pacific might be the main reason for the reduction of East Asian summer monsoon precipitation. In addition, the decreasing of the global sea level, caused by the expansion of ice sheet in high latitude, which led to more land exposure and longer transport distance of ocean water vapor, might be another cause of the East Asian summer monsoon precipitation reduction.

The Mid-Pleistocene transition (MPT) was characterized not only by the transition of ice volume periodicities from 40 kyr to 100 kyr, but also by major changes in high latitude ice sheets, global sea level and CO2 / ocean carbon storage after similar to 900 ka, which had a major influence on the evolution of the East Asian summer monsoon (EASM). However, there are different views regarding the trend of East Asian summer monsoon precipitation during the MPT and its driving mechanism. Together with published paleomagnetic and Al-26/Be-10 isotopic chronologies, we used pollen analysis of the lacustrine sediments of a drill core to reconstruct the vegetation history of the Northeast Plain of China. The results demonstrate a pattern of vegetation succession from coniferous and broadleaved mixed forest dominated by Pinus to woodland-steppe during the MPT, indicating a change from a semi-humid to a semi-arid climate. Palynological records from the Liaodong Peninsula, North China Plain, and the Tibetan Plateau also indicate a drying climate during the MPT, which was related to the decreasing trend of EASM precipitation. We suggest that falling global sea level caused by the expansion of high-latitude ice sheets, and the resulting the exposure of continental shelves and the increased transport distance of oceanic water vapor to the continental interior, was the main cause of the reduction in EASM precipitation. The weakening of the Atlantic meridional overturning circulation and the southward movement of the Intertropical Convergence Zone in the tropical Pacific may have been additional causes of the decrease in EASM precipitation.

The regional expression of moisture conditions during the Younger Dryas (YD) event and its forcing mechanism in northeastern (NE) China are controversial and more evidence is needed. Here, we present a reconstruction of changes in vegetation and precipitation during the YD event, based on pollen data from two well-dated, parallel sediment cores (TC2 and GQ2) from Tianchi Crater Lake in NE China. The elevated tree pollen abundance during the YD indicates an abrupt shift from steppe to forest, and therefore wetter conditions in Northeast China. Also, a pollen-based quantitative climatic reconstruction suggests that the climate was significantly colder and wetter, with a 3-5 degrees C decrease in annual temperature (Tann) and a 200 mm increase in annual precipitation (Pann) during the YD. To characterize the spatial distribution of moisture conditions in NE China during the YD, we also compiled 26 records from 14 sites in the region. Based on well-dated proxies, we conclude that the YD throughout northern NE China was characterized by wet conditions-significantly different from the consensus of a dry YD in southern NE China. We propose that the increased precipitation in northern NE China during the YD was a response to the strengthening of the Okhotsk High.

Documenting spatiotemporal patterns of the Holocene Optimum (HO) at the climatically sensitive East Asian monsoon (EAM) margin are essential for understanding monsoon climate dynamics. However, the timing of the onset of the HO at the EAM margin is still debated and progress has been partly hindered by age uncertainties in different proxy records. To avoid the bias of these chronological uncertainties, we compared moisture variations from the marginal EAM region reconstructed from dust and aluminum (Al) flux records with tree pollen percentages in a dated lake sediment core that tracked moisture changes in the region around the lake. We show a delay (similar to 1500 years) of HO initiation in the core EAM region in northeastern China compared to the monsoon margin. Synthesizing pollen records with reliable chronologies show a synchronous HO occurrence at similar to 8000-7000 cal yr BP at the monsoon margin, which is likely attributed to the shrinkage of the Northern Hemisphere ice sheet. Therefore, although the monsoon margin has always been considered a climate-sensitive area, it might be sensitive to different forcing factors from the core monsoon region. (c) 2023 Elsevier Ltd. All rights reserved.

Due to the worldwide attention of fossil fuel consumption and environment pollution, geothermal is recognized to be amongst the prospering alternative energy. Previous researches mainly focused on the shallow-depth geothermal heat pump systems (SD-GHPs), while medium-depth geothermal heat pump system (MD-GHPs) lacked of the experimental support especially in severely cold region. A field test of MD-GHPs using deep borehole heat exchanger (DBHE) was conducted and verified in terms of temperature variation, heat exchange and COP. The indoor temperature remained 20 & DEG;C around even though the outdoor temperature was as low as -25.10 & DEG;C. The water supply and return water temperature on the customer side performed steadfast heating characteristics that the averages were 35.13 & DEG;C and 30.97 & DEG;C. Moreover, flow rate and borehole depth are the essential influencing factors on DBHE outlet temperatures. This suggests that lifting flow rates is a fantastic option when only considering the enhancement of the thermal extraction. The DBHE average heat exchange per meter is 1000/1200 m for 61.1/84.9 W/m and 2000 m is 152.6 W/m respectively. Besides, the average heat exchange of DBHEs for working days was 485.4 kW while during Chinese New Year Holidays was 388.6 kW. Correspondingly, the average COPs for MD-GHPs ground side were 4.5 and 5.2, respectively. Results show that MD-GHPs can be extended to severely cold regions and obtain superior performance.

Land type survey is an important task of land resources survey and the basis of scientific management of land resources. With the increasingly prominent problems of population, resources, and environment, there is an urgent need for a fast and accurate classification method of large-scale land use and land cover based on remote sensing data. Traditional machine learning classification methods based on pixel classification achieved sufficient results and are widely used, such as maximum likelihood classification and random forests method. However, with the development of the novel technology of deep learning, in practical application, for multi-classified land resources, how to use the fast and effective classification method of low and medium resolution RS images needs further research. This paper takes the land resource classification of the Tonghe medium resolution RS dataset of the third land survey in China as an example to screen and compare traditional machine learning classification methods and semantic segmentation models FC-DenseNet56, GCN, BiSeNet, U-Net, DeepLabV3, AdapNet, and PSPNet, which aim to select the optimal feature extraction model. The results show that the classification accuracy of the U-Net model can reach 93.62%, which is more accurate and effective than traditional machine learning methods and other semantic segmentation models. It is suitable for multi-classification tasks of land cover resources in low and medium resolution RS images and shows a superior effect in practical application. Besides, the conclusion of this study can provide a demonstration for large-scale land cover resources investigation using low and medium resolution RS images.

More than 10% of the world's population lives in the East Asian monsoon (EAM) region, where precipitation patterns are critical to agricultural and industrial activities. However, the dominant forcing mechanisms driving spatiotemporal changes in the EAM remain unclear. We selected Holocene records tracking monsoon precipitation in the EAM region reconstructed from pollen data to explore the spatiotemporal patterns of monsoon precipitation changes. Our analysis shows a time-transgressive pattern of maximum precipitation, with earlier occurrence in the southern area and later occurrence in the northern area. The monthly insolation changes force monsoon precipitation in different parts of the EAM region through a shift in the Western Pacific Subtropical High. We conclude that low-latitude monthly insolation changes (rather than average summer insolation changes) were the main forcing mechanisms of the spatiotemporal patterns of the monsoon precipitation maximum during the Holocene.