Laohugou Glacier Research Articles

Variations of Laohugou Glacier No. 12 in the western Qilian Mountains, China, from 1957 to 2015

Glaciers were solid reservoirs and important water resources in western China, but they were retreating significantly in context of global warming. Laohugou Glacier No. 12 was the largest valley glacier in Qilian Mountains. In this study, real-time kinematic (RTK) data, topographic map and WorldView-2 satellite imagery were used to measure changes in terminus, extent and volume of Laohugou Glacier No. 12. Results showed that Laohugou Glacier No. 12 was shrinking significantly since 1957. From 1960 to 2015, the terminus reduction of Laohugou Glacier No. 12 was 402.96 m (3.99%) in total, and glacier length decreased to 9.7 km from 10.1 km. Reduction of glacier area and volume were the most obvious. From 1957 to 2015, glacier area and volume decreased by 1.54 km2 (7.03%) and 0.1816 km3, respectively. Reduction trend of terminus and area was slowing in 1950 - 1980s, even stable for a period in the mid-1980s, and then accelerated. Ice core analysis result and nearly meteorological station data shown an increasing trend of temperature in 1957 - 2015, it was a main reason of continuous retreating of Laohugou Glacier No.12.

Monitoring displacement of Laohugou glacier No. 12 based on Landsat 8 and TerraSAR-X images

采用归一化互相关算法精确配准Landsat 8影像得到了2014年—2016年不同季节冰川的运动速率，并利用其热红外波段对不同时刻的地表温度进行反演；通过强度追踪法处理TerraSAR-X影像得到了2008年4月—10月不同时段的冰川运动速率。两种数据得到的结果表明：冰川末端流速较小，中部流速增大，流速从轴部向两侧递减；冬季流速明显小于夏季，变化趋势与温度变化具有一致性。冰川西侧分支的移动速率相对较大，从Landsat 8和TerraSAR-X提取的最大速率分别为2.56 m·d-1和2.74 m·d-1。最后对稳定区域的冰川流速进行统计，结果显示Landsat 8提取的冰川流速精度控制在1—9 cm·d-1，基于TerraSAR-X的强度追踪法提取移动速率的精度控制在2 cm·d-1，验证了两种数据监测冰川移动的可靠性。

The response of surface mass and energy balance of a continental glacier to climate variability, western Qilian Mountains, China

To understand how a continental glacier responds to climate change, it is imperative to quantify the surface energy fluxes and identify factors controlling glacier mass balance using surface energy balance (SEB) model. Light absorbing impurities (LAIs) at the glacial surface can greatly decrease surface albedo and increase glacial melt. An automatic weather station was set up and generated a unique 6-year meteorological dataset for the ablation zone of Laohugou Glacier No. 12. Based on these data, the surface energy budget was calculated and an experiment on the glacial melt process was carried out. The effect of reduced albedo on glacial melting was analyzed. Owing to continuous accumulation of LAIs, the ablation zone had been darkening since 2010. The mean value of surface albedo in melt period (June through September) dropped from 0.52 to 0.43, and the minimum of daily mean value was as small as 0.1. From the records of 2010–2015, keeping the clean ice albedo fixed in the range of 0.3–0.4, LAIs caused an increase of +7.1 to +16 W m−2 of net shortwave radiation and an removal of 1101–2663 mm water equivalent. Calculation with the SEB model showed equivalent increases in glacial melt were obtained by increasing air temperature by 1.3 and 3.2 K, respectively.

Changes in precipitating snow chemistry with seasonality in the remote Laohugou glacier basin, western Qilian Mountains.

Trace elements in the atmosphere could provide information about regional atmospheric pollution. This study presented a whole year of precipitation observation data regarding the concentrations of trace metals (e.g., Cr, Ni, Cu, Mn, Cd, Mo, Pb, Sb, Ti, and Zn), and a TEM-EDX (transmission electron microscope-energy dispersive X-ray spectrometer) analysis from June 2014 to September 2015 at a remote alpine glacier basin in Northwest China, the Laohugou (LHG) basin (4200m a.s.l.), to determine the regional scale of atmospheric conditions and chemical processing in the free troposphere in the region. The results of the concentrations of trace metals showed that, although the concentrations generally were lower compared with that of surrounding rural areas (and cities), they showed an obviously higher concentration and higher EFs in winter (DJF) and a relatively lower concentration and lower EFs in summer (JJA) and autumn (SON), implying clearly enhanced winter pollution of the regional atmosphere in Northwest China. The TEM observed residue in precipitation that was mainly composed of types of dust, salt-dust, BC-fly ash-soot, and organic particles in precipitation, which also showed remarked seasonal change, showing an especially high ratio of BC-soot-fly ash particles in winter precipitation compared with that of other seasons (while organic particles were higher in the summer), indicating significant increased anthropogenic particles in the winter atmosphere. The source of increased winter anthropogenic pollutants mainly originated from emissions from coal combustion, e.g., the regional winter heating supply for residents and cement factories in urban and rural regions of Northwest China. Moderate Resolution Imaging Spectroradiometer (MODIS) atmospheric optical depth (AOD) also showed a significant influence of regional atmospheric pollutant emissions over the region in winter. In total, this work indicated that the atmospheric environment in western Qilian Mountains also showed enhanced anthropogenic pollution in winter, probably mainly caused by regional fossil fuel combustion.

Geochemical evidence for sources of surface dust deposited on the Laohugou glacier, Qilian Mountains

Atmospheric dust deposited on glacier surfaces can decrease snow albedo by enhancing lighting absorption and by forming cryoconites via microbial activity, which accelerates glacier melt. Using snow and cryoconite sampled from the Laohugou Glacier No.12 in the Qilian Mountains during spring 2012 and summer 2014, this work investigates the SrNd isotopic and rare earth element (REE) geochemistry of dust and its environmental significance. Results demonstrate that dust REEs possess lower Eu/Eu* and L/HREE, and higher (Gd/Yb)N values compared with that of the Mu Us and Hobq Deserts but yield higher (La/Yb)N, L/HREE, (La/Sm)N and (La/Yb)N ratios than that of the Taklimakan Desert. The REE composition of glacier surface dust is similar to the material from nearby arid regions, such as the Qaidam Basin and the Tengger and Badain Jaran Deserts surrounding the eastern Tibetan Plateau. The εNd(0) values of glacial dust resemble the isotopic ratios of the Qaidam, Badain Jaran, Tengger Deserts and local dust (εNd(0) value of −13.6) but differ from that of the Taklimakan Desert, which has higher 87Sr/86Sr ratios. Analysis of air mass trajectory also indicates a potential dust input from the surrounding areas to the alpine glaciers in the Qilian Mountains. These results strongly indicate that the dust source from the arid, northern Tibetan Plateau region was the dominant contributor to atmospheric dust deposition on the glacier surface, rather than dust originating from the long-range transport of Taklimakan Desert material.

Mapping Glacier Elevations and Their Changes in the Western Qilian Mountains, Northern Tibetan Plateau, by Bistatic InSAR

Accurate measurements of glacier surface topography and their changes play an essential role in various glaciological studies related to glacier dynamics and mass balance. The focus of this study is on mapping glacier digital elevation model (DEM) and elevation changes in the western Qilian Mountains, northern Tibetan Plateau, by synergistically using the TanDEM-X (TDX) bistatic Interferometric Synthetic Aperture Radar (InSAR) data in 2013 and Shuttle Radar Topography Mission (SRTM) DEM in 2000. The first high-resolution and high-precision glacier DEM is derived in this region by a TDX InSAR procedure with a nonlocal (NL) filter. Validated against the Ice, Cloud, and land Elevation Satellite (ICESat) height references, the absolute height error of the TanDEM-X DEM derived with the NL filter and the Goldstein filter with the parameters investigated is, respectively, 1.493 ± 0.747 and 1.857 ± 1.709 m. Further, four combinations of differential phase method (DiffPha) and DEM differencing method (DiffDem) with Goldstein filter and NL filter are applied to estimate glacier elevation changes between 2000 and 2013. The synergistic use of the DiffPha method and the NL filter is superior to other three combinations in terms of uncertainty and noise reduction. Generally, a clear surface thinning can be found in most glacier tongue regions, the maximum value of elevation lowering up to approximately −40 m, whereas a slight thickening is detected in accumulation areas, which are in agreement with the height difference results between GPS measurements and SRTM DEM over Laohugou Glacier No.12. This study demonstrates the potential of the TanDEM-X bistatic InSAR in mapping surface topography and elevation changes of valley glaciers in the Tibetan Plateau.

Temporal and diurnal analysis of trace elements in the Cryospheric water at remote Laohugou basin in northeast Tibetan Plateau

An evaluation of glacial meltwater chemistry is needed under recent dramatic glacier melting when water resources might be significantly impacted. This study investigated trace elements variation in the meltwater stream, and its related aquatic environmental information, at the Laohugou (LHG) glacier basin (4260 m a.s.l.) at a remote location in northeast Tibetan Plateau. We focused on the spatial, temporal and diurnal change of trace elements during the glacier ablation period. Results showed evident elements spatial difference on the glacier surface meltwater, as most of the elements showed increased concentration at the terminus compared to higher elevations sites. Dominant elements in the meltwater were Ba, Sr and Cr, whereas elements with high enrichment factors (EFs) were Sb, Ni, Mo and Zn. Temporal change of some trace elements concentration (e.g. Sc, Cu, and Rb) indicated increasing trend with accelerated snow-ice melting, whereas others (e.g. Ni, Zn, and Pb) showed decreasing trend. We find that, trace elements showed evident diurnal change and a peak value of concentration was observed each day at about 15:00–17:00, and the diurnal change was influenced by runoff level and pH. Moreover, EFs calculations revealed that heavy metals were partially originated from regional anthropogenic sources. Overall, the accelerated diurnal and temporal snow-ice melting (with high runoff level) were correlated to increased elemental concentration, pH, EC and elemental change mode, and thus this work is of great importance for evaluating the impacts of accelerated glacier melting to meltwater chemistry and downstream ecosystem in the northeast Tibetan Plateau.

Concentration, sources and light absorption characteristics of dissolved organic carbon on a medium-sized valley glacier, northern Tibetan Plateau

Abstract. Light-absorbing dissolved organic carbon (DOC) constitutes a major part of the organic carbon in glacierized regions, and has important influences on the carbon cycle and radiative forcing of glaciers. However, few DOC data are currently available from the glacierized regions of the Tibetan Plateau (TP). In this study, DOC characteristics of a medium-sized valley glacier (Laohugou Glacier No. 12, LHG) on the northern TP were investigated. Generally, DOC concentrations on LHG were comparable to those in other regions around the world. DOC concentrations in snow pits, surface snow and surface ice (superimposed ice) were 332 ± 132, 229 ± 104 and 426 ± 270 µg L−1, respectively. The average discharge-weighted DOC of proglacial stream water was 238 ± 96 µg L−1, and the annual DOC flux released from this glacier was estimated to be 6949 kg C yr−1, of which 46.2 % of DOC was bioavailable and could be decomposed into CO2 within 1 month of its release. The mass absorption cross section (MAC) of DOC at 365 nm was 1.4 ± 0.4 m2 g−1 in snow and 1.3 ± 0.7 m2 g−1 in ice, similar to the values for dust transported from adjacent deserts. Moreover, there was a significant relationship between DOC and Ca2+; therefore, mineral dust transported from adjacent arid regions likely made important contributions to DOC of the glacierized regions, although contributions from autochthonous carbon and autochthonous/heterotrophic microbial activity cannot be ruled out. The radiative forcing of snow pit DOC was calculated to be 0.43 W m−2, demonstrating that DOC in snow needs to be taken into consideration in accelerating melt of glaciers on the TP.

Provenance of cryoconite deposited on the glaciers of the Tibetan Plateau: New insights from Nd‐Sr isotopic composition and size distribution

AbstractThis study presents the Nd‐Sr isotopic compositions and size distributions of cryoconite deposited on the glaciers at different locations on the Tibetan Plateau, in order to trace its source areas and the provenance of long‐range transported (LRT) Asian dust on the Tibetan Plateau. The result of scanning electron microscope‐energy dispersive X‐ray spectrometer analysis indicated that mineral dust particles were dominant in the cryoconite. Most of the cryoconite samples from the Tibetan Plateau indicated different Sr and Nd isotopic composition compared with sand from large deserts (e.g., the Taklimakan and Qaidam deserts). Some cryoconite samples showed very similar Nd‐Sr isotopic ratios compared with those of nearby glacier basins (e.g., at Laohugou Glacier No.12, Dongkemadi Glacier, and Shiyi Glacier), indicating the potential input of local crustal dust to cryoconite. The volume‐size distribution for the cryoconite particles also indicated bimodal distribution graphs with volume median diameters ranging from 0.57 to 20 µm and from 20 to 100 µm, demonstrating the contribution of both LRT Asian dust and local dust inputs to cryoconite. Based on the particle size distribution, we calculated a mean number ratio of local dust contribution to cryoconite ranging from 0.7% (Baishui Glacier No.1) to 17.6% (Shiyi Glacier) on the Tibetan Plateau. In general, the marked difference in the Nd‐Sr isotopic ratios of cryoconite compared with those of large deserts probably indicates that materials from the western deserts have not been easily transported to the hinterland of Tibetan Plateau by the Westerlies under the current climatic conditions, and the arid deserts on the Tibetan Plateau are the most likely sources for cryoconite deposition. The resistance of the Tibetan Plateau to the Westerlies may have caused such phenomena, especially for LRT eolian dust transported over the Tibetan Plateau. Thus, this work is of great importance in understanding the large‐scale eolian dust transport and climate over the Tibetan Plateau.

Individual particles of cryoconite deposited on the mountain glaciers of the Tibetan Plateau: Insights into chemical composition and sources

Cryoconite deposited on mountain glacier surfaces is significant for understanding regional atmospheric environments, which could influence the albedo and energy balance of the glacier basins, and maintain the glacial microbiology system. Field observations were conducted on the glaciers of western China, including Laohugou Glacier No.12 (LHG), Tanggula Dongkemadi Glacier (TGL), Zhadang Glacier (ZD), and Baishui Glacier No.1 in the Yulong Mountains (YL), as well as Urumqi Glacier No.1 in the Tianshan Mountains (TS) for comparison with locations in the Tibetan Plateau, in addition to laboratory TEM-EDX analysis of the individual cryoconite particles filtered on lacey carbon (LC) and calcium-coated carbon (Ca-C) TEM grids. This work provided information on the morphology and chemical composition, as well as a unique record of the particle’s physical state, of cryoconite deposition on the Tibetan Plateau. The result showed that there is a large difference in the cryoconite particle composition between various locations on the Tibetan Plateau. In total, mineral dust particles were dominant (>50%) in the cryoconite at all locations. However, more anthropogenic particles (e.g., black carbon (BC) and fly ash) were found in YL (38%) and ZD (22%) in the Ca-C grids in the southern locations. In TGL, many NaCl and MCS particles (>10%), as well as few BC and biological particles (<5%), were found in cryoconite in addition to mineral dust. In TS, the cryoconite is composed primarily of mineral dust, as well as BC (<5%). Compared with other sites, the LHG cryoconite shows a more complex composition of atmospheric deposition with sufficient NaCl, BC, fly ash and biological particles (6% in LC grid). The higher ratio of anthropogenic particles in the southern Tibetan Plateau is likely caused by atmospheric pollutant transport from the south Asia to the Tibetan Plateau. Cryoconite in the northern locations (e.g., TGL, LHG, and TS) with higher dust and salt particle ratio are influenced by large deserts in central Asia. Therefore, the transport and deposition of cryoconite is of great significance for understanding regional atmospheric environment and circulation. Large amounts of biological, NaCl and MCS particles were observed in the cryoconite, implying that in addition to dust and BC, many types of light absorbing impurities (LAI) together could influence the glacier albedo change and induce ice melting in the mountain glaciers of the Tibetan Plateau. Moreover, a high BC concentration in the south (e.g., YL and ZD) could significantly change the albedo of snow and ice, at a greater rate than dust, causing significant melting of the glaciers under global warming.

Variations in annual accumulation recorded in a Laohugou ice core from the northeastern Tibetan Plateau and their relationship with atmospheric circulation

Annual accumulation was reconstructed for a period from 1960 to 2006 using a 21.2-m ice core from the firn basin of Laohugou (LHG) Glacier No. 12 on the northeastern Tibetan Plateau (TP). Significant periodicity of LHG accumulation variations was identified as a quasi-3-year period in accordance with the oscillation of precipitation in the northwestern China, especially the Hexi Corridor. Furthermore, the relationships of LHG accumulation with atmospheric circulation and moisture sources were investigated. LHG accumulation was positively correlated with the 500-hPa geopotential height and pressure in Central Asia, as well as the autumn Northern Atlantic Oscillation, suggesting that the Westerlies may transport moisture to the LHG region and enhance precipitation. In addition, a negative relationship between LHG accumulation and meridional wind indicated that an intense Mongolian cyclone caused by a strong meridional wind in the region could block Arctic air masses from the LHG region. Moisture fluxes and backward air mass trajectories suggested that moisture might originate from Central Asia, Southern and the inland TP. The relationship between LHG accumulation and atmospheric circulation provides an opportunity to reconstruct the history of atmospheric circulation using a deep ice core record.

Glacier meltwater runoff process analysis using δD and δ18O isotope and chemistry at the remote Laohugou glacier basin in western Qilian Mountains, China

Stable hydrogen and oxygen isotope has important implication on water and moisture transportation tracing research. Based on stable hydrogen (δD) and oxygen (δ18O) isotope using a Picarro L1102-i and water chemistry (e.g. major ions, pH, EC and TDS) measurement, this study discussed the temporal variation and characteristics of stable hydrogen and oxygen isotope, chemistry (e.g. TDS, pH, EC, Ca2+, Mg2+, Na+ and Cl-) in various water bodies including glacier meltwater runoff, ice and snow, and precipitation at the Laohugou glacier basin during June 2012 to September 2013. Results showed that δD and δ18O in the meltwater runoff varied obviously with the temporal change from June to September, showing firstly increasing trend and then decreasing trend, with the highest values in July with high air temperature and strong glacier melting, which could indicate the temporal change of glacier melting process and extent. Variations of δD and δ18O in the runoff were similar with that of snow and ice on the glacier, and the values were also above the GMWL, which probably implied that the glacier runoff was mainly originated from glacier melting and precipitation supply. The glacier meltwater chemical type at the Laohugou glacier basin were mainly composed by Ca-Na-HCO3-SO4 and Ca-Mg-HCO3-SO4, which also varied evidently with the glacier melting process in summer. By analyzing the temporal change of stable hydrogen and oxygen isotope and chemistry in the melting period, we find it is easy to separate the components of the snow and ice, atmospheric precipitation and melt-runoff in the river, which could reflect the change process of glacier melting during the melting period, and thus this work can contribute to the glacier runoff change study of large-scale region by stable isotope and geochemical method in future.

Variations of the alpine precipitation from an ice core record of the Laohugou glacier basin during 1960–2006 in western Qilian Mountains, China

The net accumulation record of ice core is one of the most reliable indicators for reconstructing precipitation changes in high mountains. A 20.12 m ice core was drilled in 2006 from the accumulation zone of Laohugou Glacier No.12 in the northeastern Tibetan Plateau, China. We obtained the precipitation from the ice core net accumulation during 1960–2006, and found out the relationship between Laohugou ice core record and other data from surrounding sites of the northeastern Tibetan Plateau. Results showed that during 1960–2006, the precipitation in the high mountains showed firstly an increasing trend, while during 1980 to 2006 it showed an obvious decreasing trend. Reconstructed precipitation change in the Laohugou glacier basin was consistent with the measured data from the nearby weather stations in the lower mountain of Subei, and the correlation coefficient was 0.619 (P<0.001). However, the precipitation in the high mountain was about 3 times more than that of the lower mountain. The precipitation in Laohugou Glacier No.12 of the western Qilian Mountains corresponded well to the net accumulation of Dunde ice core during the same period, tree-ring reconstructed precipitation, the measured data of multiple meteorological stations in the northeastern Tibetan Plateau, and also the changes of adjacent PDSI drought index. Precipitation changes of the Laohugou glacier basin and other sites of the northeastern Tibetan Plateau had significantly positive correlation with ENSO, which implied that the regional alpine precipitation change was very likely to be influenced by ENSO.

Preliminary Study on Effects of Glacial Retreat on the Dominant Glacial Snow Bacteria in Laohugou Glacier No. 12

One impact of climate change is the rapid shrinking of glaciers, resulting in microorganisms deposited into glacial snow or ice being exposed to new environments such as glacier foreland. A pyrosequencing analysis based on the bacterial 16S rRNA gene showed that bacterial diversity was the highest in proglacial soil, followed by that of glacial snow in ablation zone, then by that of glacial snow in the accumulation area, finally by that of glacial snow in glacier terminus, with the combination of Chao1, ACE, Shannon and Simpson analysis. Eighteen phyla were detected from the 7 samples, but mainly composed of Proteobacteria, Actinobacteria and Bacteroidetes. Flavobacterium, Massilia, Pedobacter, Polaromonas were more abundant in glacial snow samples than in glacial soil sample. Massilia was rarely reported in other environments, implying the necessity for its conservation under scenarios of glacier and snowpack loss induced by climate change.

Mercury distribution and variation on a high-elevation mountain glacier on the northern boundary of the Tibetan Plateau

In July 2013, snow/ice and streamwater samples were retrieved from a high-elevation mountain glacier (Laohugou Glacier No. 12) on the northern boundary of the Tibetan Plateau and were analysed for total Hg (HgT). Concentration levels of HgT in snow samples were higher than those from the central and southern part of the Tibetan Plateau. Most of the Hg in the snow/ice was found to be associated with particulate matter. A small daily variation of HgT in surface snow further suggested that snow Hg on the Tibetan Plateau was less influenced by the effect of post-depositional processes such as photoreduction. The variations in HgT peak concentration on the vertical profiles of the snowpits indicated that settling of particulate matter and percolation of snowmelt had caused an increase in Hg concentrations with increasing depth. No positive relationship was found between HgT and elevation in our study region, indicating that the “altitude effect” on Hg in surface snow may only exist on extremely high-elevation glaciers. Moreover, HgT concentrations in the surface ice were found to be the highest observed in this glacier. With ongoing climate warming, this is of particular concern in western China as the accumulated Hg released by accelerated glacier thinning and retreat may endanger ecosystems and human health in the glacier-fed downstream regions.

Physicochemical impacts of dust particles on alpine glacier meltwater at the Laohugou Glacier basin in western Qilian Mountains, China

This work discusses the temporal variation of various physicochemical species in the meltwater runoff of Laohugou Glacier No. 12 (4260ma.s.l.) in central Asia, and their correlation with dust particles, based on a two-year field observation in summer 2012 and 2013, mainly focusing on dust concentration and size distribution, meltwater chemistry, particles SEM–EDX analysis in the meltwater, and MODIS atmospheric optical depth fields around the Qilian Mountains in central Asia. We find that, the volume–size distribution of dust particles in the meltwater is mainly composed of three parts, which includes fine aerosol particles (with diameter of 0~3.0μm, mainly PM 2.5), atmospheric dust (with diameter of 3.0~20μm), and local dust particles (20~100μm), respectively. Comparison of dust particles in the snowpack and meltwater runoff indicates that, large part of dust particles in the meltwater may have originated from atmospheric dust deposition to the snow and ice on the glacier, and transported into the meltwater runoff. Moreover, temporal variation of dust and major ions (especially crustal species) is very similar with each other, showing great influence of dust particles to the chemical constituents of the glacier meltwater. SPM and TDS implied significant influences of dust to the physical characteristics of the glacier meltwater. Results showed that, accelerated glacier melting may affect physicochemical characteristics of the meltwater at an alpine basin under global warming. MODIS atmospheric optical depth (AOD) fields derived using the Deep Blue algorithm, showed great influence of regional dust transportation over western Qilian Mountains in springtime. SEM–EDX analysis shows that dust particles in the glacier meltwater contain Si-, Al-, Ca-, K-, and Fe-rich materials, such as quartz, albite, aluminate, and fly ash, similar to that deposited in snowpack. These results showed great and even currently underestimated influences of atmospheric dust deposition to glacier meltwater physicochemistry at an alpine basin in central Asia.

Ablation modeling and surface energy budget in the ablation zone of Laohugou glacier No. 12, western Qilian mountains, China

AbstractGlacier surface melting can be described using energy-balance models. We conducted a surface energy budget experiment to quantify surface energy fluxes and to identify factors affecting glacial melt in the ablation zone of Laohugou glacier No. 12, western Qilian mountains. The surface energy budget was calculated based on data from an automatic weather station, and turbulent fluxes calculated using the bulk-aerodynamic approach were corrected using measurements from an eddy-covariance system. Simulated mass balances were validated by stake observations. Net shortwave radiation was the primary component of the surface energy balance (126Wm–2), followed by sensible heat flux. Net longwave radiation (–45Wm–2) and latent heat flux (–12.8 Wm–2) represented heat sinks. The bulk-aerodynamic method underestimated sensible and latent heat fluxes by 3.4 and 1.2 W m–2, respectively. The simulated total mass balance of –1703mmw.e. exceeded the observed total by 90 mm w.e. Daily positive accumulated temperature and low albedo were the main factors accelerating glacier melt. An uncertainty assessment showed that mass balance was very sensitive to albedo and varied by 36% when albedo changed by 0.1.

A 47-year high resolution chemistry record of atmospheric environment change from the Laohugou Glacier No. 12, north slope of Qilian Mountains, China

Based on a 20.12 m shallow ice core drilled at the Laohugou Glacier No. 12 (39°25.7′N, 96°33.4′E, 5040 m a.s.l.), north slope of Qilian Mountains in the northeastern Qinghai–Tibetan Plateau in June 2006, the changes of atmospheric environment over the Qilian Mountains and northwestern China recorded by ice chemistry and its possible connection with atmospheric circulation and the winter North Atlantic Oscillation (NAO) are investigated. A total of 606 samples were analyzed for major ions (Ca2+, Na+, K+, Mg2+, NH4+, Cl−, SO42− and NO3−) and stable oxygen isotope ratios (δ18O). The ion chemistry of the ice core, covering the past 47 years, is mainly characterized by mineral dust species (Ca2+, Na+, Mg2+, SO42−, Cl− and K+), and anthropogenic species (SO42−, NH4+ and NO3−). Ca2+ is the dominant cation in the ice core with a medium value of 2815.5 μeq L−1, accounting for 65.8% of the total cations, and SO42− is the predominant anion with a medium value of 1500.4 μeq L−1, accounting for 45.8% of the total anions. Compared with ice core records from Altai and Himalayas, at the northern and southern margin of western China, respectively, dust-related species concentrations in the Laohugou ice core are much higher due to pronounced regional crustal dust aerosol inputs from surrounding arid and semiarid deserts. The results show that dust species concentrations decreased during 1960–2006 A.D., while non-dust species (SO42−, NH4+ and NO3−, anthropogenic species) concentrations increased, which indicating that the ice core record of dust storm activity over Qilian Mountains exhibits a significant decreasing trend during the past 47 years. This change of dust species may be caused by decrease in wind speed and increase in precipitation over the Laohugou surrounding areas in Qilian Mountains and northwestern China, and wind speed decrease is probably caused by spatial differences of inter-decadal air temperature change of the 600 hPa in central Asia. The normalized time series of the winter NAO index shows a significant inverse correlation with the annual flux of Ca2+ in dust, implying a possible connection between the winter NAO and the dust storm activity over the Qilian Mountains.

The Surface Energy Budget in the Accumulation Zone of the Laohugou Glacier No. 12 in the Western Qilian Mountains, China, in Summer 2009

The energy balance of a glacial surface can describe physical melting processes. To expand the understanding of how glaciers in arid regions respond to climate change, the energy budget in the accumulation zone of the Laohugou Glacier No. 12 was measured. Input variables were meteorological data (1 June—30 September 2009) from an automatic weather station located on the accumulation zone at 5040 m above sea level (a.s.l.). Radiative fluxes directly measured, and turbulent fluxes calculated using the bulk aerodynamic approach, were involved in the surface energy budget. Net radiation flux was the primary source of the surface energy balance (72%) and was chiefly responsible for glacial melting, followed by sensible heat flux (28%). Melting energy was the main output of surface energy (48%), and was almost as large as the sum of latent heat flux (32%) and subsurface heat flux (20%). The modeled mass balance was -75 mm water equivalent, which compared well with sonic ranging sensor readings. Albedo varied between 0.52 and 0.88 on the glacial surface, and melting was prevented by high albedo. Under the assumption of neutral atmospheric conditions, turbulent fluxes were overestimated, especially the sensible heat flux by 54%; therefore, a stability correction was necessary.