In this work, samples of surface snow, surface ice, snow pit and meltwater from the Laohugou Glacier No. 12 on the northern edge of Tibetan Plateau (TP) were collected during the summer of 2015. The average concentration of Hg in surface snow/ice was 22.41 ng L-1, while the percentage of dissolved mercury (Hg-D) was observed to be around 26%. An altitudinal magnification of Hg was not observed for surface snow; however, in contrast, a significant positive magnification of Hg with altitude was observed in the surface ice. A higher concentration of Hg corresponded with the dust layer of the snow pit. It was observed that about 42% of Hg was lost from the surface snow when the glacier was exposed to sunlight within the first 24 h indicating some Hg was emitted back to the atmosphere while some were percolated downwards. The result from the principal component analysis (PCA) showed that the sources of Hg in Laohugou Glacier No. 12 were from crustal and biomass burning. Finally, it was estimated that total export of Hg from the outlet river of Laohugou glacier No. 12 in the year 2015 was about 1439.46 g yr(-1) with yield of 22.77 mu g m(2) yr(-1). This study provides valuable insights for understanding the behavior of Hg in the glacier of the northern Tibetan Plateau.

Laohugou glacier No. 12 (LHG12), located in the northeast of the Qinghai-Tibet Plateau, is the largest valley glacier in the Qilian mountains. Since 1957, LHG12 has shrunk significantly. Due to the limitations of in situ observations, simulations and investigations of LHG12 have higher levels of uncertainty. In this study, consumer-level, low-altitude microdrones were used to conduct repeated photogrammetry at the lower part of LHG12, and a digital orthophoto map (DOM) and a digital surface model (DSM) with a resolution at the centimeter scale were generated, from 2017 to 2021. The dynamic parameters of the glacier were detected by artificial and automatic extraction methods. Using a combination of GNSS and drone-based data, the dynamic process of LHG12 was analyzed. The results show that the terminus of LHG12 has retreated by 194.35 m in total and by 19.44 m a(-1) on average during 2008-2021. The differential ablation leading to terminus retreat distance markedly increased during the study period. In 2019-2021, the maximum annual surface velocity was 6.50 cm day(-1), and during ablation season, the maximum surface velocity was 13.59 cm day(-1), 52.17% higher than it is annually. The surface parameters, motion, and mass balance characteristics of the glacier had significant differences between the west and east branches. The movement in the west branch is faster than it is in the east branch. Because of the extrusion of the two ice flows, there is a region with a faster surface velocity at the ablation area. The ice thickness of LHG12 is decreasing due to intensified ablation, leading to a deceleration in the surface velocity. In large glaciers, this phenomenon is more obvious than it is in small glaciers in the Qilian mountains.

Despite projections of extreme reduction in glacier volume in the Qilian Mountains by the end of the century, comprehensive studies of regional glacier-wide mass and energy balance characteristics remain lacking. This study undertook a comparative analysis of the surface energy and mass balance characteristics of Laohugou glacier No. 12 (LHG glacier) in the Shule River Basin (western Qilian Mountains) and Bailanghe glacier No. 21 (BLH glacier) in the Heihe River Basin (middle Qilian Mountains) based on in situ measurements from September 2020 to August 2021. During the cold season (September-April), precipitation was greater on the BLH glacier than on the LHG glacier. This resulted in a more positive mass balance on the BLH glacier during the cold season, and less melting in May-June owing to the higher incoming shortwave radiation. During the ablation season (May-August), snowfall was greater on the LHG glacier owing to its higher elevation, while melting was also greater owing to the anomalously low cloud fraction during summer 2021. The annual mass balance was notably more negative on the LHG glacier than on the BLH glacier at the same elevation below 5000 m, whereas the annual glacier-wide mass balance was just slightly more negative on the LHG glacier than on the BLH glacier because most of the area in the LHG glacier is at higher elevation. The equilibrium line altitude varied between 4900 and 5100 on the glaciers of Qilian Mountains during recent two decades, which signified that only 5.8-25.5% of the total glacier area is within the accumulation zone in the Heihe River Basin; thus, further global warming will place the regional glaciers in a very vulnerable position.

With global warming, glaciers in the high mountains of China are retreating rapidly. However, few data have been reported on whether greenhouse gases from these glaciers are released into the atmosphere or absorbed by glacial meltwater. In this study, we collected meltwater and ice samples from Laohugou Glacier No. 12 in western China and measured CH4 and CO2 concentrations. Meltwater from the glacier terminus was continually sampled between 3 and 5 August 2020 to measure CH4 and CO2 concentrations. The results demonstrated that meltwater is a source of CH4 because the average saturations are over 100%. It could be concluded that CH4 in the atmosphere can be released by glacial meltwater. However, the CO2 saturations are various, and CO2 fluxes exhibit positive (released CO2) or negative (absorbed CO2) values because the water and atmospheric conditions are variable. More importantly, the CH4 and CO2 concentrations were higher in meltwater samples from the glacier terminus than in samples from the surface ice (including an ice core) and a surface stream. Although the meltwater effect from the upper part of the glacier cannot be excluded, we speculated that subglacial drainage systems with an anaerobic environment may represent the CH4 source, but it needs to be further investigated in the future. However, high mountain glaciers are currently ignored in global carbon budgets, and the increased melting of glaciers with global warming may accelerate the absorption of much more CO2 and lead to the release of CH4.

Simple Summary Adaptative extremophiles are frequently found in various glacial ecological niches, such as glacial meltwater, ice, snow, and permafrost. However, no systematic study has investigated the diverse and temporary survival of culturable bacteria in newly exposed moraines around glacier snouts. The findings of this study revealed the diversity of culturable heterotrophic bacteria in a newly exposed moraine and demonstrated the evolution, competition, and selective growth of bacteria facing primary succession. This study not only helps to understand the high diversity of culturable bacteria in the newly exposed moraine at a glacier snout but also provides a theoretical basis for the study of microbial resources surviving in the transition region between glaciers and retreats. Laohugou Glacier No. 12 is located on the northern slope of the western Qilian Mountains with a temperate continental wet climate and an extremely cold winter. Bacteria in a newly exposed moraine have to cope with various pressures owing to deglaciation at the glacier snout. However, limited information is available regarding the high diversity and temporary survival of culturable heterotrophic bacteria under various environmental stresses. To examine the tolerance of extremophiles against varying environmental conditions in a newly exposed moraine, we simulated environmental stress in bacterial cultures. The results showed that the isolated strains belonged to actinobacteria, Proteobacteria, Bacteroidetes, Deinococcus-Thermus, and Firmicutes. Actinobacteria was the most abundant phylum, followed by Proteobacteria, at both high and low temperatures. Pseudarthrobacter was the most abundant genus, accounting for 14.2% of the total isolates. Although several microorganisms grew at 10 degrees C, the proportion of microorganisms that grew at 25 degrees C was substantially higher. In particular, 50% of all bacterial isolates grew only at a high temperature (HT), whereas 21.4% of the isolates grew at a low temperature (LT), and 38.6% of the isolates grew at both HT and LT. In addition, many radiation-resistant extremophiles were identified, which adapted to both cold and oxidative conditions. The nearest neighbors of approximately >90% of bacteria belonged to a nonglacial environment, such as oil-contaminated soil, rocks, and black sand, instead of glacial niches. This study provides insights into the ecological traits, stress responses, and temporary survival of culturable heterotrophic bacteria in a newly exposed moraine with variable environmental conditions and the relationship of these communities with the non-glacial environment. This study may help to understand the evolution, competition, and selective growth of bacteria in the transition regions between glaciers and retreats in the context of glacier melting and retreat owing to global warming.

Solid precipitation is not only the main supply for glacier mass, but also exerts an important influence on surface albedo and intensifies glacier melting. However, precipitation type observation is very scarce in the high alpine glaciers, which limits the precise simulation of glacier mass balance. This study assessed three discrimination methods of precipitation types including Ding method, Dai method and Froidurot method based on surface albedo observation data on the Laohugou Glacier No. 12 (LHG Glacier) in western Qilian Mountains. The results showed that Ding method had a best applicability on the LHG Glacier, the other two need to calibrate parameters when they are used in the high elevation glacier region. Then we fitted the relationship between snowfall probability and fresh snow albedo, and put forward a revised formula to simulate fresh snow albedo based on Ding method, which is expected to reduce the uncertainty in glacier mass and energy balance model. Finally, we found a best air temperature threshold of 4 degrees C for discriminating monthly precipitation types. In order to accurately simulate the glacier melt, it is necessary to obtain the threshold temperature appropriately in different glacier region with different elevation and humidity.