Glacial responses to climate change exhibit considerable heterogeneity. Although global glaciers are generally thinning and retreat, glaciers in the Karakoram region are distinct in their surging or advancing, exhibiting nearly zero or positive mass balance-a phenomenon known as the Karakoram Anomaly. This anomaly has sparked significant scientific interest, prompting extensive research into glacier anomalies. However, the dynamics of the Karakoram anomaly, particularly its evolution and persistence, remain insufficiently explored. In this study, we employed Landsat reflectance data and Moderate Resolution Imaging Spectroradiometer (MODIS) MCD43A3 albedo products to developed high-resolution albedo retrieval models using two machine learning (ML) regressions--random forest regression (RFR) and back-propagation neural network regression (BPNNR). The optimal BPNNR model (Pearson correlation coefficient [r] = 0.77-0.97, unbiased root mean squared error [ubRMSE] = 0.056-0.077, RMSE = 0.055-0.168, Bias = -0.149 similar to -0.001) was implemented on the Google Earth Engine cloud-based platform to estimate summer albedo at a 30-m resolution for the Karakoram region from 1990 to 2021. Validation against in-situ albedo measurements on three glaciers (Batura, Mulungutti and Yala Glacier) demonstrated that the model achieved an average ubRMSE of 0.069 (p < 0.001), with RMSE and ubRMSE improvements of 0.027 compared to MODIS albedo products. The high-resolution data was then used to identify firn/snow extents using a 0.37 threshold, facilitating the extraction of long-term firn-line altitudes (FLA) to indicate the glacier dynamics. Our findings revealed that a consistent decline in summer albedo across the Karakoram over the past three decades, signifying a darkening of glacier surfaces that increased solar radiation absorption and intensified melting. The reduction in albedo showed spatial heterogeneity, with slower reductions in the western and central Karakoram (-0.0005-0.0005 yr(-1)) compared to the eastern Karakoram (-0.006 similar to -0.01 yr(-1)). Notably, surge- or advance-type glaciers, avalanche-fed glaciers and debris-covered glaciers exhibited slower albedo reduction rates, which decreased further with increasing glacier size. Additionally, albedo reduction accelerated with altitude, peaking near the equilibrium-line altitude. Fluctuations in the albedo-derived FLAs suggest a transition in the dynamics of Karakoram glaciers from anomalous behavior to retreat. Most glaciers exhibited anomalous behavior from 1995 to 2010, peaking in 2003, but they have shown signs of retreat since the 2010s, marking the end of the Karakoram anomaly. These insights deepen our understanding of the Karakoram anomaly and provide a theoretical basis for assessing the effect of glacier anomaly to retreat dynamics on the water resources and adaptation strategies for the Indus and Tarim Rivers.

Background Stable carbon isotope composition (delta C-13(p)) can be used to estimate the changes in intrinsic water use efficiency (iWUE) in plants, which helps us to better understand plants' response strategies to climate change. This study focused on the variations in delta C-13(p) and iWUE for the different life-form plants (i.e., herbs, shrubs, and trees) along an altitudinal gradient (3300, 3600, 3900, 4100, 4300, and 4500 m) on the eastern slope of Yulong Snow Mountain, southeastern margin of the Qinghai-Tibet Plateau. The response mechanisms of delta C-13(p) and iWUE for different life-form plants to altitude were thoroughly analyzed in this mountain ecosystem. Results The delta C-13(p) values of plants on the eastern slopes of Yulong Snow Mountain ranged from - 30.4 parts per thousand to - 26.55 parts per thousand, with a mean of - 28.02 parts per thousand, indicating a dominance of C-3 plants. The delta C-13(p) and iWUE values varied among different life-form plants in the order of herbs > shrubs > trees, particularly in 3600, 3900, and 4300 m. The delta C-13(p) and iWUE values for herbs and shrubs increased with altitude and were mainly controlled by air temperature. The two parameters for trees exhibited a trend of initial decrease followed by an increase with altitude. Below 3900 m, the delta C-13(p) and iWUE values decreased with altitude, influenced by soil moisture. However, above 3900 m, the two parameters increased with altitude, mainly regulated by air temperature. In addition, iWUE was positively correlated with leaf P content but negatively correlated with leaf N:P ratio, especially for herbs and trees, suggesting that P plays a key role in modulating iWUE in this region. Conclusions The differentiated responses of water availability for different life-form plants to a higher altitudinal gradient are regulated by air temperature, soil moisture, and leaf P content in the Yulong Snow Mountain. These results provide valuable insights into understanding the water-carbon relationships in high-altitude ecosystems.

Tropical high-Andean wetlands, locally known as 'bofedales', are key ecosystems sustaining biodiversity, carbon sequestration, water provision and livestock farming. Bofedales' contribution to dry season baseflows and sustaining water quality is crucial for downstream water security. The sensitivity of bofedales to climatic and anthropogenic disturbances is therefore of growing concern for watershed management. This study aims to understand seasonal water storage and release characteristics of bofedales by combining remote sensing analysis and ground-based monitoring for the wet and dry seasons of late 2019 to early 2021, using the glacierised Vilcanota-Urubamba basin (Southern Peru) as a case study. A network of five ultrasound loggers was installed to obtain discharge and water table data from bofedal sites across two headwater catchments. The seasonal extent of bofedales was mapped by applying a supervised machine learning model using Random Forest on imagery from Sentinel-2 and NASADEM. We identified high seasonal variability in bofedal area with a total of 3.5% and 10.6% of each catchment area, respectively, at the end of the dry season (2020), which increased to 15.1% and 16.9%, respectively, at the end of the following wet season (2021). The hydrological observations and bofedal maps were combined into a hydrological conceptual model to estimate the storage and release characteristics of the bofedales, and their contribution to runoff at the catchment scale. Estimated lag times between 1 and 32 days indicate a prolonged bofedal flow contribution throughout the dry season (about 74% of total flow). Thus, our results suggest that bofedales provide substantial contribution to dry season baseflow, water flow regulation and storage. These findings highlight the importance of including bofedales in local water management strategies and adaptation interventions including nature-based solutions that seek to support long-term water security in seasonally dry and rapidly changing Andean catchments.

The distinct climatic and geographical conditions make high-altitude permafrost on the Tibetan Plateau suffer more severe degradation than polar permafrost. However, the microbial responses associated with greenhouse gas production in thawing permafrost remain obscured. Here we applied nanopore-based long-read metagenomics and high-throughput RNA-seq to explore microbial functional activities within the freeze-thaw cycle in the active layers of permafrost at the Qilian Mountain. A bioinformatic framework was established to facilitate phylogenetic and functional annotation of the unassembled nanopore metagenome. By deploying this strategy, 42% more genera could be detected and 58% more genes were annotated to nitrogen and methane cycle. With the aid of such enlarged resolution, we observed vigorous aerobic methane oxidation by Methylomonas, which could serve as a bio-filter to mitigate CH4 emissions from permafrost. Such filtering effect could be further consolidated by both on-site gas phase measurement and incubation experiment that CO2 was the major form of carbon released from permafrost. Despite the increased transcriptional activities of aceticlastic methanogenesis pathways in the thawed permafrost active layer, CH4 generated during the thawing process could be effectively consumed by the microbiome. Additionally, the nitrogen metabolism in permafrost tends to be a closed cycle and active N2O consumption by the topsoil community was detected in the near-surface gas phase. Our findings reveal that although the increased thawed state facilitated the heterotrophic nitrogen and methane metabolism, effective microbial methane oxidation in the active layer could serve as a bio-filter to relieve the overall warming potentials of greenhouse gas emitted from thawed permafrost. On-site MinION metagenomics and RNA-seq were combined to explore microbial functionalities of active layers of the soil of Qilian Mountain permafrost. With the developed annotation pipeline-FUNpore, 42% more genera and 58% more genes were detected. Active methane consumption by Methylomonas could serve as a biofilter to mitigate CH4 emission from permafrost. Dissimilatory nitrate reduction to ammonia pathway enabled a closed microbial nitrogen cycle and N2O consumption was observed. image On-site MinION metagenomics and RNA-seq were combined to explore microbial functionalities of active layers of the soil of Qilian Mountain permafrost. With the developed annotation pipeline-FUNpore, 42% more genera and 58% more genes were detected. Active methane consumption by Methylomonas could serve as a biofilter to mitigate CH4 emission from permafrost. Dissimilatory nitrate reduction to ammonia pathway enabled a closed microbial nitrogen cycle and N2O consumption was observed.

For summer-accumulation-type glaciers, the glaciological literature is lacking studies on determining the snow line altitude (SLA) from optical images at the end of the summer as an indicator of the equilibrium line altitude (ELA). This paper presents a workflow for extracting the SLA from Landsat images based on the variation in the albedo with the altitude in the central line area of glaciers. The correlation of >0.8 at the 99% confidence level between the retrieved SLAs with ELAs derived from the interpolation of ground-based, mass balance measurements indicated that the workflow can be applied to derive the SLA from end-of-summer satellite data as an indicator of ELA. The ELA was under-estimated by the calculated SLA. The relationship between the end-of-summer SLA and the ELA depends on the intensity of glacier melting. Subsequently, the workflow was applied to the seven glaciers in the Eastern Tien Shan Mountains, and a time series of the SLA was obtained using 12 end-of-summer Landsat scenes from 1994 to 2016. Over the whole study period, a mean SLA of 4011.6 +/- 20.7 m above sea level (a.s.l.) was derived for the seven investigated glaciers, and an increasing SLA was demonstrated. The increase in SLAs was consistent for the seven glaciers from 1994 to 2016. Concerning the spatial variability, the east-west difference was prominent, and these differences exhibited a decreasing trend. The average SLA of each glacier is more influenced by its morpho-topographic variables. The interannual variations in the average SLA are mainly driven by the increasing summer air temperature, and the high correlation with the cumulative summer solid precipitation reflects the characteristics of the summer-accumulation-type glaciers.

Aeolian dust has a great influence on mountain hydrology, climate, and biogeochemical cycles. Dust deposited on glaciers and snowpack of the high alpine mountains in Tibetan Plateau (TP) and its surrounding regions can provide a unique method of determining the high-elevation transport and deposition of Asian dust in the middle and upper troposphere. Long-range-transported (LRT) Asian dust is often transmitted through the high troposphere, thus studies on dust deposition in the high-elevation cryosphere can reflect the LRT information of aeolian dust, and provide an unparalleled record to understand the regional climate and environment change in the Third Pole region. This paper comprehensively reviews the current status of the major factors that determine aeolian dust transport, settling, and cycling, and the key components of this dust-cycles in high elevation cryosphere regions, revealed by glacial snowpack and ice-core dust geochemistry recorded in the mountain glacier areas of TP and western China. Research on glacial dust concentrations indicated that much higher amounts of aeolian dust were found to transport and cycle in the high-elevation troposphere over TP and surroundings, compared to other locations of the globe. Dust concentrations and fluxes in high elevation regions of the TP were closely related to the transport distance of the nearby dust sources (e.g. large deserts and Gobi in western China, and arid deserts on the plateau surface). Isotopes tracers (e.g. Sr-87/Sr-86, and epsilon(Hf), epsilon(Nd)) and dust size distributions revealed that aeolian dust transported over TP mainly originated from the arid and semi-arid deserts and surface crust soils on TP; Aeolian dust from the large deserts of central Asia (e.g. the Taklimakan Desert with small ratio) have not been easily transported to the hinterland of TP under the current climatic conditions. An End-Member Mixing Analysis model was also used to calculate the relative contributions of northern hemisphere dust sources to the TP glacier dust sinks. The marked spatial differences in LRT dust sources of TP glaciers were caused by the large-scale atmospheric circulation strength and interactions in the Asian region. In addition, Asian dust has a large influence on the radiative forcing of glacier and snow melt in which the iron oxide composition constitute an important driving factor. Biogeochemical cycles in cryospheric regions were significantly affected by aeolian dust cycles, influencing glacial ecosystems, meltwater geochemistry (e.g. d(Fe) release) and nutrients supply for downstream aquatic ecosystems. Ice core records for the past hundred years revealed a general decreasing trend of dust storm frequency and atmospheric concentration over the TP region. This work provides new insights and perspectives on aeolian dust transport and cycling in high regions of the troposphere and cryosphere of the TP, identifying critical uncertainties and priorities for future research.

Analysis of the climatology of aerosol properties is performed over Hanle (4500 m) and Merak (4310 m), two remote-background sites in the western trans-Himalayas, based on eleven years (2008-2018) of sun/sky radiometer (POM-01, Prede) measurements. The two sites present very similar atmospheric conditions and aerosol properties allowing us to examine them as continuous single-data series. The annual average aerosol optical depth at 500 nm (AOD(500)) is 0.04 +/- 0.03, associated with an Angstrom exponent (AE(440-870)) of 0.58 +/- 0.35 and a single scattering albedo (SSA(500)) of 0.95 +/- 0.05. AOD(500) exhibits higher values in May (similar to 0.07) and lower in winter (similar to 0.03), while AE(400-870) minimizes in spring, indicating influence by coarse-mode dust aerosols, either emitted regionally or long-range transported. The de-convolution of AOD(500) into fine and coarse modes justifies the aerosol seasonality and sources, while the marginal diurnal variation in all aerosol properties reveals a weak influence from local sources, except for some few aerosol episodes. The aerosol-volume size distribution presents a mode value at similar to 10 mu m with secondary peaks at accumulation (similar to 2 mu m) and fine modes (similar to 0.03 mu m) and low variability between the seasons. A classification of the aerosol types based on the fine-mode fraction (FMF) vs. SSA(500) relationship reveals the dominance of aerosols in the FMF range of 0.4-0.6, characterized as mixed (39%), followed by fine aerosols with high scattering efficiency (26%), while particles related to dust contribute similar to 21%, with low fractions of fine-absorbing aerosols (similar to 13%). The aerosol radiative forcing (ARF) estimates reveal a small cooling effect at the top of the atmosphere (-1.3 Wm(-2)), while at the surface, the ARF ranges from -2 Wm(-2) to -6 Wm(-2) on monthly basis. The monthly-mean atmospheric radiative forcing (similar to 1 to 4 Wm(-2)) leads to heating rates of 0.04 to 0.13 K day(-1). These ARF values are higher than the global averages and may cause climate implications over the trans-Himalayan region. (C) 2020 Elsevier B.V. All rights reserved.

The altitude effect of isotopes in precipitation is not as significant on the leeward side of a mountain as it is on the windward side, which makes it difficult to use isotopes at leeward sites, especially if estimating elevation of groundwater recharge or reconstructing paleoelevations. Samples of precipitation were taken at three stations with different elevations-2,306-3,243 m above mean sea level (asl)-on the leeward side of the Meili Snow Mountains on the southeastern Tibetan Plateau from August 2017 to July 2018. The isotope vs. altitude gradients were calculated based on two adjacent stations at the daily, monthly, and annual scales. Most of the gradients are beyond the global ranges of -0.5 to -0.1 parts per thousand per 100 m for delta O-18 and -5 to -1 parts per thousand per 100 m for delta H-2, and some of the gradients are even positive. Local processes of sub-cloud evaporation and mixing with recycled moisture are identified for the ambiguous altitude effect, while regional atmospheric circulation processes dominate the major patterns of stable isotope variation at the three stations. The groundwater recharge elevation is estimated to be in a very large range, 2,562-6,321 m asl, which could be caused by the differences in isotope vs. altitude gradient in the studied catchments. Considering the complex atmospheric processes affecting precipitation isotopes, sampling of event-based/monthly precipitation at more than two altitudes for at least one complete hydrological year is a minimum requirement to establish a reasonable isotope vs. altitude gradient.

The simultaneous near surface measurements of aerosol scattering and absorption coefficients over different environments (Ahmedabad, urban and Gurushikhar, a high altitude remote site) in western India were conducted to estimate SSA and investigate the importance of SSA in aerosol radiative forcing. The surface SSA (0.79, 0.85) is lower than the column SSA (0.92, 0.95) as emission sources for black carbon aerosols (absorbing in nature) are abundant near the surface (Ahmedabad, Gurushikhar). The atmospheric warming over the urban region estimated using column SSA is a factor of 3 lower ( similar to 18 Wm(-2)) than that of the warming ( similar to 52 Wm(-2)) estimated utilising surface SSA. The significant difference in atmospheric warming arises due to the differences in the SSA as aerosol optical depth (a measure of column concentration of aerosols) is the same. Surface and column SSA are comparatively higher over the high altitude remote site as the abundance of absorbing aerosols is less over a non-source region. In addition, the differences between surface and column SSA are less (< 9%) resulting in comparable aerosol radiative forcing estimates. This study highlights the differences that can arise in aerosol radiative effects due to the differences in SSA as a function of altitude (surface vs. column) and environment (urban vs. remote), thereby providing regional bounds on aerosol radiative forcing which can further be used in climate assessment studies.

Wildfires inject large amounts of black carbon (BC) particles into the atmosphere, which can reach the lowermost stratosphere (LMS) and cause strong radiative forcing. During a 14-month period of observations on board a passenger aircraft flying between Europe and North America, we found frequent and widespread biomass burning (BB) plumes, influencing 16 of 160 flight hours in the LMS. The average BC mass concentrations in these plumes (similar to 140 ng.m(-3), standard temperature and pressure) were over 20 times higher than the background concentration (similar to 6 ng.m(-3)) with more than 100-fold enhanced peak values (up to similar to 720 ng.m(-3)). In the LMS, nearly all BC particles were covered with a thick coating. The average mass equivalent diameter of the BC particle cores was similar to 120 nm with a mean coating thickness of similar to 150 nm in the BB plume and similar to 90 nm with a coating of similar to 125 nm in the background. In a BB plume that was encountered twice, we also found a high diameter growth rate of similar to 1 nm.h(-1) due to the BC particle coatings. The observed high concentrations and thick coatings of BC particles demonstrate that wildfires can induce strong local heating in the LMS and may have a significant influence on the regional radiative forcing of climate.