Glaciers provide multiple ecosystem services (ES) to human society. Due to the continued global warming, the valuation of glacier ES is of urgent importance because this knowledge can support the protection of glaciers. However, a systematic valuation of glacier ES is still lacking, particularly from the perspective of ES contributors. In this study, we introduce the concept of emergy to establish a methodological framework for accounting glacier ES values, and take the Tibetan Plateau (TP) as a case study to comprehensively evaluate the spatiotemporal characteristics of glacier ES during the early 21st century. The results show that the total glacier ES values on the TP increased from 2.36E+24 sej/yr in the 2000s to 2.40E+24 sej/yr in the 2010s, with an overall growth rate of 1.6%. The values of the various services in the 2010s are ranked in descending order: climate regulation (1.59E+24 sej/yr, 66.1%), runoff regulation (4.40E+23 sej/yr, 18.4%), hydropower generation (1.88E+23 sej/ yr, 7.8%). Significantly higher glacier ES values were recorded in the marginal TP than in the endorheic area. With the exception of climate regulation and carbon sequestration, all other service values increased during the study period, partially cultural services, which have experienced rapid growth in tandem with social development. The results of this study will help establish the methodological basis for the assessment of regional and global glacier ES, as well as a scientific basis for the regional protection of glacier resources.

The Tian Shan mountain range, known as the water towers of Central Asia, plays a key role in local water supply, yet large uncertainties remain about the amount of water that is stored in its glaciers. In this study, we assess the impact of the boundary conditions on ice thickness estimates using two inversion models: a mass conservation (MC) model and a basal shear stress (BS) model. We compare the widely used Randolph Glacier Inventory version 6 with the updated Glacier Area Mapping for Discharge from the Asian Mountains glacier inventory, as well as two digital elevation models (SRTM DEM and Copernicus DEM). The results show that the ice volume (in similar to 2000 CE) in the Tian Shan range is 661.0 +/- 163.5 km(3) for the MC model and 552.8 +/- 85.3 km(3 )for the BS model. There are strong regional differences due to inventory, especially for glaciers in China (17-25%). However, the effect of different DEM sources on ice volume estimation is limited. By the end of the 21st century, the projected mass loss differences between inventories are higher than between adjacent emission scenarios, illustrating the vital importance of high-quality inventories. These differences should be carefully considered during water resource planning.

Understanding the dynamics of glaciers is essential for the knowledge of global sea-level rise, local freshwater resources in high mountain and arid regions, and the potential glacial hazards. In this paper, we present a two-dimensional thermomechanically coupled ice flow model named PoLIM (Polythermal Land Ice Model). The velocity solver of PoLIM is developed based on the Blatter-Pattyn approximation of Stokes flow. It uses an enthalpy formulation of the energy balance, an approach that is suitable for modeling the polythermal glaciers. PoLIM also includes a scheme for gravity-driven drainage of water in temperate ice, a subglacial hydrology model coupled with ice dynamics, and multiple basal sliding laws. The model has been verified by standard benchmark problems, including the ISMIP-HOM experiments, the enthalpy benchmark experiments, and the SHMIP experiments. PoLIM shows good performances and agrees well with these benchmark results, indicating its robust capability of simulating the thermomechanical behaviors of glaciers.

Investigating the characteristics and transformation of water-soluble carbonaceous matter in the cryosphere regions is important for understanding biogeochemical process in the earth system. Water-soluble carbonaceous matter is a heterogeneous mixture of organic compounds that is soluble in aquatic environments. Despite its importance, we still lack systematic understanding for dissolved organic carbon (DOC) in several aspects including exact chemical composition and physical interactions with microorganisms, glacier meltwater. This review presents the chemical composition and physical properties of glacier DOC deposited through anthropogenic emission, terrestrial, and biogenic sources. We present the molecular composition of DOC and its effect over snow albedo and associated radiative forcings. Results indicate that DOC in snow/ice is made up of aromatic protein-like species, fulvic acid-like materials, and humic acid-like materials. Light-absorbing impurities in surface snow and glacier ice cause considerable albedo reduction and the associated radiative forcing is definitely positive. Water-soluble carbonaceous matter dominated the carbon transport in the high-altitude glacial area. Owing to prevailing global warming and projected increase in carbon emission, the glacial DOC is expected to release, which will have strong underlying impacts on cryosphere ecosystem. The results of this work have profound implications for better understanding the carbon cycle in high altitude cryosphere regions. A new compilation of globally distributed work is required, including large-scale measurements of glacial DOC over high-altitude cryosphere regions, to overcome and address the scientific challenges to constrain climate impacts of light-absorbing impurities related processes in Earth system and climate models.

Accelerated melting of mountain glaciers due to global warming has a significant impact on downstream biogeochemical evolution because a large amount of labile dissolved organic matter (DOM) is released. However, the DOM evolution processes from glacier to downstream are not well understood. To investigate these processes, samples from the glacial surface and terminating runoff of a mountain glacier on the Tibetan Plateau were collected simultaneously throughout the melting season. The samples were analyzed to determine the dissolved organic carbon (DOC) contents and chemical compositions by means of a combination of fluorescence excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results indicate that the DOC concentrations were higher in the snow samples than in the glacial runoff samples, although a significantly higher concentration of inorganic ions was found in the glacial runoff samples, suggesting the dominant source of DOM in the glacial runoff was the glacier. The EEM-PARAFAC revealed four fluorescent components in both the snow and glacial runoff samples. However, significantly different ratios between the four components of these two categories of samples suggested chemical, physical and/or biological evolution of DOM during transport. Molecular chemical composition analyses by FT-ICR MS revealed that the DOM composition varied dramatically between the glacier and the glacial runoff. More than 50 % of the molecules were transformed from aliphatic and peptide-like compounds in the snow samples into highly unsaturated and phenolic-like compounds in the glacial run-off samples. The potential chemical transformation of DOM was likely related to biological and/or photolytic evolution during transport. Our results suggest that chemical evolution of glacial DOM could occur during the downstream transport, which is expected to be useful for further research exploring the fate of DOM and carbon cycling from the ciyaspheric environment and evaluating the biogeochemical effects.

Surface albedo is an important driver of surface processes that promote glacier melting and is a key variable influencing glacier surface melt. Despite much focus in the literature on variations in albedo and its influence on snow surfaces, little attention has been paid to dust and its impact on bare-ice albedo with respect to glacier melting surfaces. In this paper, spatial changes in glacier albedo were investigated using three Landsat images taken during the ablation season in 2006; temporal variations in albedo were measured by an automatic weather station (AWS) in the ablation zone between 26 June and 1 August 2007 at Urumqi Glacier No. 1 in Tien Shan. Ice and snow samples and reflection spectra at 325-1050 nm were collected in August, 2007 at Urumqi Glacier No. 1. The data suggested that spatial changes in glacier albedo are not prominent after snowfall; however, once ice becomes exposed, glacier albedo varies remarkably and generally increases with elevation, especially around the snow line. Temporal variations are characterized by a large range and high frequency, and most are induced by snowfall, changes in cloud conditions, and surface dust; snowfall and cloud increase glacier albedo. Furthermore, the response of snow albedo is more sensitive to cloud compared with the response of ice albedo. Over a bare ice surface, the albedo generally decreases as the concentration of surface dust increases. Organic matter is a primary factor in reducing the albedo over ice.

Atmospheric nitrogen deposition is an important contributor to global and regional nitrogen cycles, and atmospheric nitrogen could be a critical limit nutrient for remote areas. In this study, nitrogen species compositions, deposition fluxes, and historical records in the mountains of Western China, including the Tibetan Plateau, were determined from snowpit and ice core samples collected from mountain glaciers. The mean concentration of total dissolved nitrogen (TDN) in the snowpit samples was 12.6 mu mol L-1 (8.0-17.8 mu mol L-1) and comprised 59% ammonium nitrogen, 35% nitrate nitrogen, and similar to 6% dissolved organic nitrogen. The deposition of nitrogen species, except organic nitrogen (likely due to its low concentrations and/or different origination), varied seasonally in a similar way based on the records of the snowpit profile. Based on monthly surface sample collection in one of the glaciers, the mass concentration and composition of nitrogen species varied monthly, mainly because of melting processes. During melting, the inorganic nitrogen content could be lost significantly, whereas the dissolved organic nitrogen concentration could be enriched because of microbial activity. For the historical records, the nitrogen deposition in mountain areas of Western China after 1960s was increased by about one time of that during 1900-1950 and was dominated by ammonium-N. From the snowpit data, we estimated the total dissolved nitrogen deposition flux at 0.56-1.3 (mean 0.88) kg ha(-1) a(-1) in the mountain area of Western China. These results could improve our understanding of nitrogen deposition and cycle in the mountain areas of Western China.

Investigating the characteristics and transformation of water-soluble carbonaceous matter in the cryosphere regions is important for understanding biogeochemical process in the earth system. Water-soluble carbonaceous matter is a heterogeneous mixture of organic compounds that is soluble in aquatic environments. Despite its importance, we still lack systematic understanding for dissolved organic carbon (DOC) in several aspects including exact chemical composition and physical interactions with microorganisms, glacier meltwater. This review presents the chemical composition and physical properties of glacier DOC deposited through anthropogenic emission, terrestrial, and biogenic sources. We present the molecular composition of DOC and its effect over snow albedo and associated radiative forcings. Results indicate that DOC in snow/ice is made up of aromatic protein-like species, fulvic acid-like materials, and humic acid-like materials. Light-absorbing impurities in surface snow and glacier ice cause considerable albedo reduction and the associated radiative forcing is definitely positive. Water-soluble carbonaceous matter dominated the carbon transport in the high-altitude glacial area. Owing to prevailing global warming and projected increase in carbon emission, the glacial DOC is expected to release, which will have strong underlying impacts on cryosphere ecosystem. The results of this work have profound implications for better understanding the carbon cycle in high altitude cryosphere regions. A new compilation of globally distributed work is required, including large-scale measurements of glacial DOC over high-altitude cryosphere regions, to overcome and address the scientific challenges to constrain climate impacts of light-absorbing impurities related processes in Earth system and climate models.

The exploration of the spatiotemporal distribution of greenhouse gas (GHG) exchange in the cryosphere (including ice sheet, glaciers, and permafrost) is important for understanding its future feedback to the atmosphere. Mountain glaciers and ice sheets may be potential sources of GHG emissions, but the magnitude and distribution of GHG emissions from glaciers and ice sheets remain unclear because observation data are lacking. In this study, in situ CH 4 and CO 2 and the mixing ratios of their carbon isotope signatures in the air inside an ice cave were measured, and CH 4 and CO 2 exchange in the meltwater of Laohugou glacier No. 12, a high-mountain glacier in an arid region of western China, was also analyzed and compared with the exchange in downstream rivers and a reservoir. The results indicated elevated CH 4 mixing ratios (up to 5.7 ppm) and depleted CO 2 (down to 168 ppm) in the ice cave, compared to ambient levels during field observations. The CH 4 and CO 2 fluxes in surface meltwater of the glacier were extremely low compared with their fluxes in rivers from the Tibetan Plateau (TP). CH 4 and CO 2 mixing ratios in the air inside the ice cave were mainly controlled by local meteorological conditions (air temperature, wind speed and direction) and meltwater runoff. The carbon isotopic compositions of CH 4 and CO 2 in the ice cave and terminus meltwater indicated 6 13 C-CH 4 depletion compared to ambient air, suggesting an acetate fermentation pathway. The abundances of key genes for methanogenic archaea/genes encoding methyl coenzyme M reductase further indicated the production of CH 4 by methanogenic archaea from the subglacial meltwater of high -mountain glaciers. The discovery of CH 4 emissions from even small high -mountain glaciers indicates a more prevalent characteristic of glaciers to produce and release CH 4 from the subglacial environment than previously believed. Nevertheless, further research is required to understand the relationship between this phenomenon and glacial dynamics in the third pole.

The glaciers in the Sawir Mountains are an important freshwater resource, and glaciers have been experiencing a continuing retreat over the past few decades. However, studies on detailed glacier mass changes are currently sparse. Here, we present the high-precision evolution of annual surface elevation and geodetic mass changes in the ablation area of the Muz Taw Glacier (Sawir Mountains, China) over the latest three consecutive mass-balance years (2017-2020) based on multi-temporal terrestrial geodetic surveys. Our results revealed clearly surface lowering and negative geodetic mass changes, and the spatial changing patterns were generally similar for the three periods with the most negative surface lowering (approximately -5.0 to -4.0 m a(-1)) around the glacier terminus. The gradient of altitudinal elevation changes was commonly steep at the low elevations and gentle in the upper-elevation parts, and reduced surface lowering was observed at the glacier terminus. Resulting emergence velocities ranged from 0.11 to 0.86 m a(-1) with pronounced spatial variability, which was mainly controlled by surface slope, ice thickness, and the movement of tributary glaciers. Meanwhile, emergence velocities slightly compensated the surface ablation at the ablation area with a proportion of 14.9%, and dynamic thickening had small contributions to glacier surface evolution. Limited annual precipitation and glacier accumulation may result in these weak contributions. Higher-resolution surveys at the seasonal and monthly scales are required to get insight into the mass balance processes and their mechanism.