Glacier-fed streams (GFSs) export large amounts of suspended sediment (SS) and associated mercury, with important implications for downstream water quality, yet the controls on Hg export remain poorly constrained. This issue is particularly acute on the Tibetan Plateau, where glacier meltwater sustains major Asian rivers. Here, we quantify seasonal and diurnal variability (n = 350) in SS and Hg across six Tibetan Plateau GFSs and synthesize observations from 36 GFSs worldwide. Tibetan Plateau GFSs exhibit total Hg (THg) concentrations and yields comparable to Alaska, but higher than most GFSs with similar glacier coverage. In GFSs without proglacial lakes, THg export scales with SS and increases with glacier coverage and velocity, indicating mobilization of erosion-derived, particle-associated Hg. THg-SS hysteresis differs among glacier thermal regimes in response to particle sorting and subglacial drainage evolution. Our results suggest that intensifying melt and rainfall on the Tibetan Plateau may increase Hg yields and delay the timing of peak Hg export, whereas expanding proglacial lakes may temporarily buffer further downstream Hg export. This study identifies controls on SS and THg export in Tibetan Plateau GFSs and highlights implications for downstream water quality and ecosystem exposure under glacier retreat.

Midsommersø records the Holocene glacial history of Wandel Dal, Inutoqqat Nunaat (Peary Land) northern Greenland

Changes in glacier meltwater runoff in the Qilian Mountains situated on the northeastern edge of the Tibetan Plateau are important for sustaining water resources in the arid regions of Northwest China. Combining multi-period remote sensing, historical data and modeling, we evaluate the glacier mass and area changes as well as associated runoff change of all glaciers in the area. Glacier area shrunk by 516.8 km 2 (∼26%, 0.53% ± 0.15% a −1 ) between 1970 and 2020 and glacier surface elevation change was −0.35 ± 0.04 m a −1 between 2000 and 2014. In general, glaciers in the eastern Qilian Mountains retreated faster than those in the western part. A mass balance model calibrated against geodetic estimates derived from DEM differencing was used to reconstruct annual glacier mass changes and runoff from 1990 to 2017. Across the 11 glacierized large-scale river basins (0.02%–2.5% glacierization), the index-based glacier runoff ratio relative to basin water input ranged from 0.1% to 6.2%. Results show an increase in glacier runoff volumes during 1990–2001, but no statistically significant trend thereafter (2002–2017) despite increasing glacier thinning. This slowdown is attributed to decreasing glacier area as the glaciers retreated. Overall, our findings highlight that while glacier runoff continues to play a critical role in sustaining river runoff in the Qilian Mountains, its buffering effect is weakening as glacier runoff approach peak water, implying increasing vulnerability of regional water resources to precipitation variability under future climate change.

The Tibetan Plateau (TP), a critical sentinel for tracking long-range atmospheric transport (LRAT) of anthropogenic pollutants, provides indispensable archives for evaluating historical pollutant dynamics in pristine ecosystems. This study investigated temporal variations of 26 per- and polyfluoroalkyl substances (PFASs) in four alpine lake sediment cores across the TP spanning 1952-2020. Total PFAS concentrations ranged from 43.7 to 1428 pg g-1 of dw. Linear regression of log-transformed PFAS concentration revealed a significant elevation-dependent trend across the studied lakes (R2 = 0.58, p < 0.01) after excluding the lower-altitude, more human-impacted Qinghai Lake (3190 m), supporting mountain cold-trapping of these pollutants in high-altitude environments. Ranwu Lake demonstrated a unique PFAS profile dominated by perfluorobutanoic acid (PFBA), which contributed 48% of total PFASs on average, reflecting the predominant influence of glacier meltwater input pathways. The deposition flux exhibited an overall increasing trend, with fluctuations between 7.62 and 258 pg cm-2 a-1 during the studied period. Following a phase of relative stability or slight decline in the 1980s-1990s, all lakes showed a pronounced and sustained rise after 2000. Notably, the doubling time of short-chain PFBA (C4) flux in these lakes was estimated to be 7.4-15.6 years since the post-2000 period. Compositional analysis revealed a global shift from long-chain to short-chain PFASs in TP lake sediments, as reflected by declining PFOS (C8) and rapidly increasing levels of PFBA. The sedimentary record reveals temporal PFAS trends that closely track the historical evolution of global and regional PFAS emissions. Our findings provide crucial insights into the long-term trends of PFAS pollution in high-altitude ecosystems, contributing to global PFAS management efforts by assessing the effectiveness of regulations and the environmental impacts of industrial relocations.

Abstract. The year 2022 was extremely warm and dry in Europe, resulting in a severe hydrological drought. In Switzerland, part of Europe’s water tower, streamflow in glacier-fed rivers could have been even more reduced if the situation had not led simultaneously to extreme glacier melt. Here we analyze the role of glaciers during the 2022 drought for 88 glacierized catchments by combining streamflow and meteorological observations with estimations of snow water equivalent, actual evapotranspiration and daily glacier storage changes. We also compare the year 2022 to earlier exceptionally warm and dry years (1921, 1928, 1947, 1998, 2003 and 2018) to assess if the ongoing glacier retreat has already caused a declining meltwater supply in such extreme conditions. Results show that 60 %–80 % of the total glacier melt in 2022 came from net mass loss (imbalanced melt). During summer, the increased glacier melt could completely offset the precipitation and snowmelt deficits for catchments with around 15 % glacierization. Further downstream, the extra glacier melt in summer alleviated water input deficits by up to 5 % at Basel (Rhine) and 70 % at Porte du Scex (Rhone). Compared to past extreme years, total glacier meltwater volume has declined due to strong glacier area loss, despite higher melt rates per unit area. In 2022 versus 2003 – the most comparable recent extreme summer – total glacier meltwater supply decreased in two thirds of the catchments over the entire summer, and in one third in July. In the remaining catchments, the more intense specific melt of 2022 could offset the 21 % glacier area loss since 2003. Despite these declines, relative glacier melt contributions to streamflow stayed rather constant, or even rose in some months, highlighting its ongoing importance during droughts while simultaneously raising concerns for future drought situations.

Glaciers in the Northern Tien Shan are a major source of Ile River runoff, supplying water to Kazakhstan’s largest city, Almaty. Under ongoing climate warming, their degradation alters the magnitude and seasonality of river discharge, increasing water-resource vulnerability. This study quantifies long-term changes in glacier area, firn-line elevation, and glacier runoff in the northern Tien Shan from 1955 to 2021. The analysis uses multi-decadal meteorological observations, hydrological records, multi-temporal Landsat-7/8 and Sentinel-2 imagery, and DEMs combined with empirical and semi-empirical runoff estimation methods. The glacier area has declined by more than 45–60% since 1955, accompanied by a rise in firn-line altitude from ~3400 to 3700 m. At the Mynzhylky station, mean summer air temperature increased by 0.88 °C, reflecting persistent warming in glacierized elevations. The contribution of glacier meltwater to annual discharge decreased from ~32% in 1955–1990 to ~25% in 1991–2021, while total and vegetation-period runoff increased due to modified seasonal hydrological conditions. These results demonstrate the impact of climate warming on glacier-fed runoff in the Northern Tien Shan and highlight the need to integrate glacier degradation into water-resource management and long-term water-security assessments.

In Press Oceanologia, uncorrected, in press Polish Academy of Sciences Institute of Oceanology Open access article under the CC BY license https://doi.org/10.5697/... Glacial bay as a local hot spot for retention and accumulation of heavy metals transported with glacier meltwater (Hornsund, Svalbard)

Glacier-fed lakes are expanding, but research on the driving factors of their expansion is insufficient. The primary reason for this gap lies in the current definition of glacial lakes, which includes all lakes within 10 km of glaciers, regardless of whether they are glacier-fed or non-glacier-fed lakes, and does not consider glacier-fed lakes located more than 10 km from glaciers. To address this, this study presents a novel classification and analysis framework for glacier-fed lakes in High Mountain Asia using Landsat images and the CBAM-UNet model. We identify 17,382 glacier-fed lakes covering an area of 2,309.5 ± 223.4 km² as of 2020s. A key finding is that 21% of these lakes, accounting for 42% of the total area, are located more than 10 km from glaciers. Additionally, we highlight that the expansion of glacier-fed lakes is influenced by both glacier meltwater and precipitation. When the glacial contribution exceeds 10%, lake dynamics are predominantly driven by glacier changes. However, for lakes with a glacial contribution below 10%, precipitation plays a more significant role in shaping lake expansion. These findings offer new insights into glacier-lake interactions and provide a more accurate basis for future GLOF risk assessments in the region.

ABSTRACT Glacier meltwater streams are a source of methane (CH4) but can act as a sink for atmospheric carbon dioxide (CO2) through the weathering of minerals. Though both processes have been observed at glaciers in other regions of the world, the European Alps have so far been overlooked. Thus, we currently do not know whether, and to what extent, ongoing glacial melt in the Alps affects global warming through the release or storage of greenhouse gases (GHGs). We assess the source and sink behavior of alpine glacier streams with regard to CH4 and CO2 by analyzing meltwater immediately at the outlet of twenty-six glaciers located in the Eastern Alps (Italy, Austria, and Switzerland) once during the melt season of 2023. We found that most glacier streams were supersaturated with CH4 compared to the atmosphere. In contrast, CO2 concentrations varied considerably across the sampled streams. Overall, these glacier-fed rivers did not show elevated CH4 or CO2 concentrations nor fluxes compared to other headwater streams. However, they illustrate the complexities behind dynamic outgassing of GHGs associated with glacial melt and may thus serve as model systems to understand and predict the behavior of the globally shrinking cryosphere.

Abstract In their 1999 paper “Widespread bacterial populations at glacier beds and their relationship to rock weathering and carbon cycling,” Sharp and co‐authors initiated a paradigm shift from glaciers viewed as abiotic systems to glacier environments hosting active microbial communities and corresponding biogeochemical cycling. Since then, the field of glacier biogeochemistry has sought to elucidate how these microbes function and the consequences of their activity in glacial and proglacial environments, and for global biogeochemical cycles. Subsequent research has supported the existence of active biogeochemical cycling by the “glacial microbiome.” Paradoxically, dissolved organic matter (DOM) exported in glacier meltwater is both ancient and a labile source of organic carbon that may be readily incorporated into downstream ecosystems. Further, DOM that has been characterized in glacier systems (using both fluorescence spectroscopy and ultrahigh resolution mass spectrometry) from different locations shares specific fluorescence and molecular formulae characteristics, hinting at a potential commonality in “glacial DOM.” The recent manuscript “Gradients of Deposition and In Situ Production Drive Global Glacier Organic Matter Composition” (Holt et al., 2024, https://doi.org/10.1029/2024gb008212) addresses these two observations by employing Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR MS) to characterize DOM composition at the molecular level from glacier sites located around the globe. The use of both the powerful FT‐ICR MS technique and an unparalleled global glacier data set offers a unique insight into glacier DOM variability and commonality, and the source of ancient and/or labile DOM in glacier runoff. Further, the study provides an impetus for specific future lines of investigation.

Impact of geothermal activity on the anomalous retreat of Changmolung Glacier in the Karakoram.

Abstract Mountain glaciers offer opportunities to observe boundary layer exchanges in conditions characterized by predominantly stable stratification, thermally driven winds, and varying surface roughness. Logistical challenges involved in instrumenting glacier surfaces mean that in situ observations remain relatively scarce, limiting the use of this outdoor laboratory. The second Hintereisferner Experiment (HEFEX II) was carried out on an Austrian Alpine glacier during summer 2023. This collaborative endeavor, involving 12 institutions from Austria, France, Germany, Switzerland, and the United Kingdom, represents an unprecedented set of observations of glacier microclimate. Instrumentation on the glacier surface consisted of eight 3-m and two 5-m weather stations equipped with multilevel eddy covariance systems and auxiliary instrumentation, and eight additional lower-specification weather stations. These operated successfully for 26 days with minimal data gaps. During a 3-day intensive observational period, additional instrumentation was deployed: a short-path ultrasonic anemometer installed very close to the glacier surface; a high-speed thermal camera capturing high-resolution boundary layer heat transport at the glacier centerline on a synthetic screen; 3D sampling of the glacier boundary layer using two meteorological UAVs; and a Streamline XR Doppler lidar capturing the structure of the above-valley atmosphere. These novel datasets are valuable for improving understanding of glacier–atmosphere exchange processes, the role of glaciers in valley circulation, and how both might be affected by continued climate change and glacier recession. Here, we detail the scientific goals and implementation of the campaign, describe the general weather conditions, and present first insights into what the observations reveal about the glacier boundary layer features observed during the campaign. Significance Statement The second Hintereisferner Experiment (HEFEX II) deployed extensive instrumentation on an Austrian glacier in summer 2023 to investigate glacier microclimate, turbulence properties, and multiscale atmosphere–glacier exchanges. Such observations are of value because (i) the stably stratified, persistent katabatic flow over glaciers offers a real-world laboratory in which to test turbulent theory; (ii) they enable refined quantification of the atmosphere–glacier exchanges that govern glacier meltwater production; and (iii) they allow verification of high-resolution simulations of the atmosphere that can subsequently be used to understand how ongoing glacier shrinkage will impact the wider valley circulation.

Abstract. A comprehensive understanding of groundwater–surface water (GW–SW) interactions is essential for managing water resources in arid regions, where hydrological processes are highly sensitive to climate variability and human activity. This study investigates spatial variations in GW–SW relationships across the Shule River Basin in Northwest China, based on hydrochemical and stable isotopic analyses of 31 river water and groundwater samples. Isotopic results reveal a clear altitude effect in river water, with δ18O values decreasing at a rate of −0.08 ‰ (100 m)−1, which is lower than the rate observed in the adjacent Qinghai–Tibet Plateau. In the upper reaches, river water is mainly derived from precipitation, glacier meltwater, and groundwater. In the midstream area, river water recharges groundwater at higher elevations, while spring discharge contributes groundwater back to the river at lower altitudes. In the lower reaches, irrigation return flow becomes a key recharge source for shallow groundwater. Hydrochemical results show progressive salinization along the flow path. River water total dissolved solids (TDS) increases from 371.40 mg L−1 upstream to 1072.13 mg L−1 downstream, while groundwater TDS ranges from 506.51 to 1499.65 mg L−1. River water is primarily influenced by silicate and carbonate weathering, whereas groundwater chemistry is governed by mineral dissolution and cation exchange reactions. These findings highlight strong spatial heterogeneity in water quality and GW–SW interactions. A conceptual model of the basin-scale hydrological cycle is proposed based on the above understanding. This model not only provides important insights into typical river–groundwater systems in arid regions of Northwest China but also serves as a valuable reference for analogous studies and the sustainable management of water resources in arid regions worldwide.

Monitoring the hydrological processes of lakes can provide reliable data for regional water resources assessment. This paper analyzed changes in the lake area and water level of Hala Lake from 2011 to 2023, subsequently estimating its lake water storage change (LWSC). We used image data from Landsat series satellites and multi-source satellite altimetry data, and then quantitatively assessed the influence of various driving factors on the LWSC in combination with hydrological and meteorological models. The results show three stages of parallel changes in the area, water level and LWSC of Hala Lake in the past 13 years. The first stage is from 2011 to 2014, when the lake expanded slightly, the second stage is from 2015 to 2019, when the lake expanded rapidly, and the last stage is from 2020 to 2023, with relatively stable conditions. Over the entire study period, the LWSC increased with a trend of 0.192 ± 0.009 km3/a. Lake surface precipitation, precipitation-caused runoff, and glacier meltwater contributed to the total recharge input by 51%, 40.96%, and 8.04%, respectively, while the lake surface evaporation accounted for 59.37% of the total recharge input as water loss. Thus, the left 40.63% of the input caused the LWSC increase. Although lake surface precipitation provided the primary contribution to the Hala Lake LWSC, precipitation-caused runoff was the key factor forming the three stages in the LWSC. The results of this study provide valuable information for the rational development and utilization of water resources by government departments and are also beneficial to the study of global change.

This paper presents a comparative evaluation of the hydro-meteorological factors underlying the regressive floods of 2010 and 2022 in the Swat River Basin, a climate-sensitive and topographically predisposed location in north-western Pakistan. The research examines, through the joint application of a qualitative case study method supplemented with GIS analysis, remote sensing, NASA MERRA-2 climate data, GlobeLand30, and hydrological modelling, the patterns, intensity, and effects of the two floods. The 2010 flood was mainly exacerbated by record monsoon floods that reached more than 300 per cent above average in some regions of Khyber Pakhtunkhwa, accompanied by La Niña and glacier meltwater flow, along with poor river dikes. However, unlike 2022, the flood was caused by extended monsoon rains and an intense pre monsoon heatwave, rapid glacial thaws, and rainfall as high as 243 per cent of normal. Analysis of land use indicated a greater extent of urbanisation, deforestation, and floodplain encroachment, which reduced the water absorption capacity of nature and thus increased risks. Although discharge peaks increased in 2010, runoff volume increased in 2022, due to enhanced hydrological responses. The study highlights the importance of reforestation, watershed development, flood zoning, warning systems, and hardy infrastructure in mitigating future calamities.

SummaryGlacial lakes on the Tibetan Plateau are highly sensitive to cryosphere-hydrosphere interactions under climate change. This study applies a high-resolution framework to quantify sub-daily glacier meltwater contributions and hydrological impacts using Baishui River Glacier No. 1 and Blue Moon Lake Valley as a representative case. A gradient boosting machine model simulated hourly glacier melt from meteorological inputs, capturing episodic events and diurnal variability with high accuracy (RMSE = 0.0100 m/h against observed melt). Cross-correlation revealed an average 3.99-h lag between glacier melt and lake-level response, indicating delayed routing. Feature importance analysis identified air temperature and solar radiation as dominant melt drivers. Glacier meltwater contributed 87.62% of positive lake inflow, highlighting the basin’s dependence on cryospheric inputs. This integrated approach—combining high-frequency sensing, machine learning, and lag-time analysis—advances the characterization of glacier-lake dynamics and supports more accurate hydrological prediction in glacierized mountain basins.

ABSTRACT The economy and society of Central Asia depend heavily on glacier meltwater from the Tien Shan as a water resource. However, recent global warming has altered the regional climate and melting patterns of glaciers, and an unprecedented trend of glacier retreat caused by rapid warming has been observed in the Tien Shan since the 1970s. While short‐term monitoring and climate response of glaciers are well developed, less effort has been devoted to long‐term historical fluctuations and physical mechanism studies based on climate models. Here we use a tree‐ring reconstruction and melting energy simulated by an energy balance model to study the glacier mass balance of Urumqi Glacier No. 1 for the past 400 years, with the aim of better understanding the long‐term changes in the relationship between this glacier and climate change during the summer ablation period. Our results demonstrated that surface temperature change driven by downward longwave radiation is the dominant factor affecting long‐term glacier melting. Against the background of climatic warming and humidification in northwest China, the increase in precipitation is unable to offset the melting trend caused by rising temperatures. Further analysis revealed that the dominant driver of glacier melting is the warming effect of greenhouse gas forcing. Also, aerosol forcing causes glacier melting via direct and indirect radiation effects. These findings emphasise the importance of monitoring the regional glaciers, combined with climate change research, to establish a scientific foundation for water management and environmental conservation in Central Asia.

Glacier meltwater contribution to river runoff in Western Mongolia

Iron is an essential micronutrient for phytoplankton and plays an integral role in the marine carbon cycle. The supply and bioavailability of iron are therefore important modulators of climate over glacial-interglacial cycles. Inputs of iron from the Antarctic continental shelf alleviate iron limitation in the Southern Ocean, driving hotspots of productivity. Glacial meltwater fluxes can deliver high volumes of particulate iron. Here, we show that glacier meltwater provides particles rich in iron(II) to the Antarctic shelf surface ocean. Particulate iron(II) is understood to be more bioavailable to phytoplankton, but less stable in oxic seawater, than iron(III). Using x-ray microscopy, we demonstrate co-occurrence of iron and organic carbon-rich phases, suggesting that organic carbon retards the oxidation of potentially-bioavailable iron(II) in oxic seawater. Accelerating meltwater fluxes may provide an increasingly important source of bioavailable iron(II)-rich particles to the Antarctic surface ocean, with implications for the Southern Ocean carbon pump and ecosystem productivity.

Riverine microplastics in the Mount Everest region affected by glacier meltwater.