Glaciated Regions Research Articles

Atmospheric Abundance of PM2.5 Carbonaceous Matter and Their Potential Sources at Three High-Altitude Glacier Sites over the Indian Himalayan Range

This study inspects the concentrations of fine particulate matter (PM2.5) mass and carbonaceous species, including organic carbon (OC) and elemental carbon (EC), as well as their thermal fractions in the Indian Himalayan glacier region at the western Himalayan region (WHR; Thajiwas glacier, 2799 m asl), central Himalayan region (CHR; Gomukh glacier, 3415 m asl), and eastern Himalayan region (EHR; Zemu glacier, 2700 m asl) sites, throughout the summer and winter periods of 2019–2020. Ambient PM2.5 samples were collected on quartz fiber filters using a low-volume sampler, followed by carbon (OC and EC) quantification using the IMPROVE_A thermal/optical reflectance methodology. Different seasonal variations in PM2.5 and carbonaceous species levels were found at all three sites investigated. Averaged PM2.5 mass ranged 55–87 μg m–3 with a mean of 55.45 ± 16.30 μg m–3 at WHR, 86.80 ± 35.73 μg m–3 at CHR, and 72.61 ± 24.45 μg m–3 at EHR. Among the eight carbon fractions, high-temperature OC4 (evolved at 580 °C in the helium atmosphere) was the most prevalent carbon fraction, followed by low-temperature OC2 (280 °C) and EC1 (580 °C at 2% oxygen and 98% helium). Char-EC representing incomplete combustion contributed to 56, 67, and 53% of total EC, whereas soot-EC contributed to 38, 26, and 43% of total EC in WHR, CHR, and EHR, respectively. The measured OC/EC ratios imply the presence of secondary organic carbon, whereas char-EC/soot-EC ratios suggested that biomass burning could be the predominant source of carbon at CHR, whereas coal combustion and vehicular emission might be dominant sources at WHR and EHR sites.

Supraglacial debris thickness and supply rate in High-Mountain Asia

Supraglacial debris strongly modulates glacier melt rates and can be decisive for ice dynamics and mountain hydrology. It is ubiquitous in High-Mountain Asia, yet because its thickness and supply rate from local topography are poorly known, our ability to forecast regional glacier change and streamflow is limited. Here we combined remote sensing and numerical modelling to resolve supraglacial debris thickness by altitude for 4689 glaciers in High-Mountain Asia, and debris-supply rate to 4141 of those glaciers. Our results reveal extensively thin supraglacial debris and high spatial variability in both debris thickness and supply rate. Debris-supply rate increases with the temperature and slope of debris-supply slopes regionally, and debris thickness increases as ice flow decreases locally. Our centennial-scale estimates of debris-supply rate are typically an order of magnitude or more lower than millennial-scale estimates of headwall-erosion rate from Beryllium-10 cosmogenic nuclides, potentially reflecting episodic debris supply to the region’s glaciers.

Changes in climate extremes in a typical glacierized region in central Eastern Tianshan Mountains and their relationship with observed glacier mass balance

As an icon of anthropogenic climate change, alpine glaciers are highly sensitive to climate change. However, there remain research gaps regarding trends in climate extremes in glacierized regions and their relationship with local glacier mass balance. In this study, these relationships and their underlying links were explored in a typical glacierized region in the Eastern Tianshan Mountains, China, from 1959 to 2018. All warm extremes exhibited increasing trends that intensified dramatically from the 1990s. Meanwhile, decreasing trends were found for all cold extremes except for the temperatures of the coldest days and coldest nights. All of the precipitation extremes demonstrated increasing trends, except for consecutive dry days and consecutive wet days. Statistically significant positive/negative correlations were detected between glacier mass balance and six warm extremes (TN90p, TX90p, SU99p, TR95p, TXx, and TNx)/four cold extremes (TN10p, TX10p, FD0, and ID0). Simulation results showed that the impact of the intensity/frequency of the warm extremes (TN90p, TX90p, SU99p, and TR95p) on glacier ablation was remarkable and the effect of the cold extremes (FD0 and ID0) on accumulation was also significant. Additionally, the increases in the intensity and frequency of most climate extremes seemed more remarkable in glacierized regions than in non-glacierized regions. Hence, studies on glacier-climate interactions should focus greater attention on the impacts of climate extremes on glacier evolution.

Spatial pattern of the debris-cover effect and its role in the Hindu Kush-Pamir-Karakoram-Himalaya glaciers

Supraglacial debris is widespread on the Hindu Kush-Pamir-Karakoram-Himalaya (HPKH) glaciers, which influences ice melt rates and glacier response to climate change, with important consequences for regional water resources. Supraglacial debris has shown an expanding trend with glacier shrinkage and mass loss, but knowledge about regional spatial patterns of debris cover and associated impacts on HPKH glaciers is still incomplete, which markedly affects the assessment accuracy of regional debris-covered glacier status and hydrological impacts. Here, we address these issues based on ASTER imagery, glacier inventory, and a physically-based ice melt model. We find that about 14.3 % of the regional glacier area is covered by supraglacial debris, and its thickness decreases gradually from northwest to southeast of the region overall. Except for the glaciers of western Himalaya and Karakoram, where the acceleration effect of debris cover is dominant, the insulation effect of debris cover on the glaciers of Pamir, Hindu-Kush, central and eastern Himalaya is particularly significant. The heterogeneous distribution of debris thickness and the resulting melt hotspots (ice cliffs and supraglacial ponds) enhance debris-covered surface thinning in the HPKH region, but it is not the dominant cause of surface thinning. Overall, the net effect of considering spatially distributed debris thickness can reduce total mass loss of debris-covered glaciers by 0.44 ± 0.04 m water equivalent (w. e.) yr−1. As a result, the presence of debris cover retards accelerated glacier melting caused by current climate warming, with important implications for slowing down regional water shortage and ecological environment risk in the HPKH region. Our findings highlight the importance of including the debris-cover effect in regional glacier models for assessing future glacier change and associated hydrological impacts in the HPKH region.

On Tide Aliasing in GRACE Time-Variable Gravity Observations

Aliasing error induced by tide-related high frequency mass variations is one of the most significant errors in the Gravity Recovery and Climate Experiment (GRACE). In the present work, we evaluated the 161.0-day S2, 171.2-day P1, and 322.1-day S1 ocean tide aliasing in GRACE latest RL06 data based on nearly 15 years of observation from 2002 to 2017. Tide aliasing was still obvious for current GRACE observations, especially for S2 and P1 aliasing. S2 aliasing was mostly evident over West Antarctica, and was a clearly eastward propagation that travelled around Antarctica in about 2 years, while P1 showed strongest aliasing over South Greenland. More seriously, we found that GRACE mascon data showed an extremely large aliasing error. The mascon data may have unintentionally amplified the aliasing error on land due to the regularization (or constraint) applied for reducing signal leakage. Enough attention must be paid to tide aliasing when using GRACE for assessing mass variations at high latitudes (e.g., glaciers in polar regions) which can cause potential obstacles to estimation of actual seasonality.

Ice thickness and morphological analysis reveal the future glacial lake distribution and formation probability in the Tibetan Plateau and its surroundings

Owing to intense glacial retreat and melting, it is anticipated that numerous glacial lakes will be formed in the next few decades. However, their development and distribution patterns in the Tibetan Plateau and its surroundings still need to be elucidated. In this study, a published glacier ice thickness distribution dataset was employed to fully detect overdeepened glacier beds as potential glacial lakes. We selected and expanded four morphological metrics to determine the formation probability of potential glacial lakes: surface slope, break in slope, lake area, and position on the glacier. The results revealed that 15,826 potential glacial lakes with areas >0.02 km 2 exist in the Tibetan Plateau and its surroundings, covering an area of 2253.95 ± 1291.29 km 2 with a water volume of 60.49 ± 28.94 km 3 that would contribute to an equivalent sea level rise of 0.16 ± 0.08 mm. The experimental comparison and uncertainty assessment for the overdeepening processing showed that the different extraction methods and basic digital elevation models used could lead to non-negligible errors in the results (at least ±30%), which were ignored in previous studies, contributing to major divergences between the several current inventories of potential glacial lakes in the plateau. Notably, approximately 90% of the total area of the potential glacial lakes is concentrated in the lower half of the individual glaciers in the Tibetan Plateau and its surroundings. >70% of the potential glacial lakes and contemporary glacial lakes in this region were found to be concentrated within the 4000–5800 m elevation range. Moreover, the study identified 5361 potential glacial lakes with high or very high exposure probabilities, and their distribution was mostly determined by regional glacier resources. However, the numbers and sizes of some potential glacial lakes that are found in the Karakoram region are considered to be exaggerated because of the presence of numerous surge-type glaciers, which have not been discussed in previous studies. These results can improve our understanding of future glacial lake formation and distribution in the Tibetan Plateau and its surroundings and have implications for further implementation of effective prevention, mitigation, and adaptation measures for glacial lake outburst floods and water security. • 15,826 PGLs with areas >0.02 km 2 exist in the Tibetan Plateau and its surroundings, covering an area of 2253.95 ± 1291.29 km 2 with a water volume of 60.49 ± 28.94 km 3 . • Approximately 90% of the total area of the Potential Glacial Lakes is concentrated in the lower half of the individual glaciers in the Tibetan Plateau and its surroundings. • The number and size of some Potential Glacial Lakes found in the Karakoram region are considered exaggerated because of the presence of numerous surge-type glaciers.

Re-visiting the structural and glacial history of the Shackleton Glacier region of the Transantarctic Mountains, Antarctica

ABSTRACT Only at Cape Surprise, central Transantarctic Mountains, is there exposed stratigraphic evidence for major offset along the range front, which marks a major boundary in Antarctica. Several faults parallel to the range front have been identified in the Devonian to Triassic Gondwana strata in the hinterland. Analysis of the stratigraphy based on field observations and the United States Geological Survey (USGS) aerial photographs, in conjunction with USGS topographic sheets and satellite-derived elevation measurements, suggests an array of faults with varying orientations and displacements. Fault offsets range up to an estimated 850 metres. No additional range-parallel faults have been identified and no clear pattern of faulting is evident in the hinterland of the frontal escarpment. Faulting may date from the time of slow uplift during the Cretaceous as well as the more rapid Cenozoic uplift of the range. Only a few faults in the hinterland can be allied with the fontal fault system. Cenozoic uplift and associated denudation was accompanied by glaciation of Antarctica, which is documented by Sirius Group strata. These deposits, which pre-date today’s polar landscape, are older than mid Miocene, and in part may date from the earliest stages of warm-based glaciation in the early Oligocene.

Prediction of near-surface air temperature in glacier regions using ERA5 data and the random forest regression method

Near-surface air temperature is an essential physical parameter for estimating the glacier ablation model that is significant to understanding the dynamics of the changes and constant monitoring of glaciers. There is a significant difference between the temperatures in glacier and non-glacier areas at the same altitude, and the estimation model that uses low-altitude automatic weather station (AWS) data cannot be applied to glaciers far away from the stations. In this study, a scheme for air temperature prediction using the random forest regression (RFR) model and the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis 5 (ERA5) data was analyzed. The results show that the average mean absolute error (MAE) and root mean square error (RMSE) of the ERA5 raw temperature product for three glaciers were 4.32 °C and 5.72 °C, respectively. After the RFR model revision, the MAE and RMSE significantly decreased to 1.01 °C and 1.41 °C, respectively. In addition, when the Linzhi weather station was used to calculate the temperature in the Parlung No. 4 Glacier area, the MAE of the Greuell and Böhm (GB) model decreased by 0.18 °C compared to that obtained using the lapse rate method. With our method, long time series of glacier surface air temperature data with high accuracy can be obtained by using short term in-situ temperature measurements.

Which glaciers are the largest in the world?

AbstractGlacier monitoring has been internationally coordinated for more than 125 years. Despite this long history, there is no authoritative answer to the popular question: ‘Which glaciers are the largest in the world?’ Here, we present the first systematic assessment of this question and identify the largest glaciers in the world – distinct from the two ice sheets in Greenland and Antarctica but including the glaciers on the Antarctic Peninsula. We identify the largest glaciers in two domains: on each of the seven geographical continents and in the 19 first-order glacier regions defined by the Global Terrestrial Network for Glaciers. Ranking glaciers by area is non-trivial. It depends on how a glacier is defined and mapped and also requires differentiating between a glacier and a glacier complex, i.e. glaciers that meet at ice divides such as ice caps and icefields. It also depends on the availability of a homogenized global glacier inventory. Using separate rankings for glaciers and glacier complexes, we find that the largest glacier complexes have areas on the order of tens of thousands of square kilometers whereas the largest glaciers are several thousands of square kilometers. The world's largest glaciers and glacier complexes are located in the Antarctic, Arctic and Patagonia.

Identifying potential sources of iron-binding ligands in coastal Antarctic environments and the wider Southern Ocean

The availability of iron (Fe) to marine microbial communities is enhanced through complexation by ligands. In Fe limited environments, measuring the distribution and identifying the likely sources of ligands is therefore central to understanding the drivers of marine productivity. Antarctic coastal marine environments support highly productive ecosystems and are influenced by numerous sources of ligands, the magnitude of which varies both spatially and seasonally. Using competitive ligand exchange adsorptive cathodic stripping voltammetry (CLE-AdCSV) with 2-(2-thiazolylazo)-p-cresol (TAC) as a competing artificial ligand, this study investigates Fe-binding ligands (FeL) across the continental shelf break in the Mertz Glacier Region, East Antarctica (64 - 67°S; 138 - 154°E) during austral summer of 2019. The average FeL concentration was 0.86 ± 0.5 nM Eq Fe, with strong conditional stability constants (Log KFeL) averaging 23.1 ± 1.0. The strongest binding ligands were observed in modified circumpolar deep water (CDW), thought to be linked to bacterial Fe remineralisation and potential siderophore release. High proportions of excess unbound ligands (L’) were observed in surface waters, as a result of phytoplankton Fe uptake in the mixed layer and euphotic zone. However, FeL and L’ concentrations were greater at depth, suggesting ligands were supplied with dissolved Fe from upwelled CDW and particle remineralisation in benthic nepheloid layers over the shelf. Recent sea-ice melt appeared to support bacterial production in areas where Fe and ligands were exhausted. This study is included within our newly compiled Southern Ocean Ligand (SOLt) Collection, a database of publicly available Fe-binding ligand surveys performed south of 50°S. A review of the SOLt Collection brings attention to the paucity of ligand data collected along the East Antarctic coast and the difficulties in pinpointing sources of Fe and ligands in coastal environments. Elucidating poorly understood ligand sources is essential to predicting future Fe availability for microbial populations under rapid environmental change.

Heavy metal levels and sources in suspended particulate matters of the glacier watersheds in Northeast Tibetan Plateau

This study collected summer meltwater runoff samples from several glacier watersheds of the northeast Tibetan Plateau during June-July 2017, and measured the concentrations of 17 trace elements (Li, Be, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Mo, Cd, In, Sb, Cs, Ba) in meltwater suspended particulate matter (SPM), in order to reveal the elemental concentration, spatial distribution, and water quality in remote glacier watershed under regional anthropogenic activities. Results showed that, the concentration of heavy metal elements was relatively high in Yuzhufeng Glacier basin, ranging from 0.57 μg/L (In) to 1,551.6 μg/L (Ba), whereas in Qiyi Glacier basin it was the lowest, ranging from 0.02 to 85.05 μg/L; and relatively medium in other glacier watersheds, with total elemental concentration varying from 1,503.9 to 1726.2 μg/L. Moreover, enrichment factors (EFs) of SPM heavy metals showed significantly higher value in the downstream than that of upper glacier region of the watershed. Most heavy metals with low EFs mainly originated from crust dust, while others with higher EFs (e.g., Cd, Sb) probably originated from anthropogenic sources. Spatially, the EFs of heavy metals were higher in Yuzhufeng and Laohugou Glacier basins; while in other regions the EFs were relatively low, which may be caused by regional land-surface and atmospheric environmental differences surrounding the various glacier watersheds. Compared with other remote locations in global range, heavy metals level (e.g., Cu, Ni, and Zn) in this region is relatively higher. Meanwhile, we find that, though the water quality of the glacier basin in northeast Tibetan Plateau was relatively clean and pollution-free, it is still obviously affected by regional anthropogenic activities. Mining activities, transportation and natural weathering and erosion processes in the study areas have important effects on the content of heavy metal pollutants of river-water SPM in the glacier watershed. Moreover, backward air-mass trajectories demonstrated the potential atmospheric pollutants transport from the surrounding cities and suburbs, to deposit in the snowpack and glaciers, and then melted out and released into meltwater runoff. This study provides a new perspective on more complete view of heavy metals distribution in glacier watershed, and new understanding for the cryosphere water environment evaluation in the Tibetan Plateau region.

Offset of MODIS land surface temperatures from in situ air temperatures in the upper Kaskawulsh Glacier region (St. Elias Mountains) indicates near-surface temperature inversions

Abstract. Remote sensing data are a crucial tool for monitoring climatological changes and glacier response in areas inaccessible for in situ measurements. The Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) product provides temperature data for remote glaciated areas where air temperature measurements from weather stations are sparse or absent, such as the St. Elias Mountains (Yukon, Canada). However, MODIS LSTs in the St. Elias Mountains have been found in prior studies to show an offset from available weather station measurements, the source of which is unknown. Here, we show that the MODIS offset likely results from the occurrence of near-surface temperature inversions rather than from the MODIS sensor’s large footprint size or from poorly constrained snow emissivity values used in LST calculations. We find that an offset in remote sensing temperatures is present not only in MODIS LST products but also in Advanced Spaceborne Thermal Emissions Radiometer (ASTER) and Landsat temperature products, both of which have a much smaller footprint (90–120 m) than MODIS (1 km). In all three datasets, the offset was most pronounced in the winter (mean offset >8 ∘C) and least pronounced in the spring and summer (mean offset <2 ∘C). We also find this enhanced seasonal offset in MODIS brightness temperatures, before the incorporation of snow surface emissivity into the LST calculation. Finally, we find the MODIS LST offset to be consistent in magnitude and seasonal distribution with modeled temperature inversions and to be most pronounced under conditions that facilitate near-surface inversions, namely low incoming solar radiation and wind speeds, at study sites Icefield Divide (60.68∘N, 139.78∘ W; 2,603 m a.s.l) and Eclipse Icefield (60.84∘ N, 139.84∘ W; 3017 m a.s.l.). Although these results do not preclude errors in the MODIS sensor or LST algorithm, they demonstrate that efforts to convert MODIS LSTs to an air temperature measurement should focus on understanding near-surface physical processes. In the absence of a conversion from surface to air temperature based on physical principles, we apply a statistical conversion, enabling the use of mean annual MODIS LSTs to qualitatively and quantitatively examine temperatures in the St. Elias Mountains and their relationship to melt and mass balance.

Geospatial technology-based monitoring of HAGL in the context of flash flood: A case study of Rishi Ganga Basin, India

This study, motivated by the flood disaster that took place at the glaciated region in Rishi Ganga Basin of Nanda Devi Biosphere Reserve (NDBR), Uttarakhand on 7th February 2021, intends to identify the altitudinal and sequential changes in the glacier region using satellite imageries. Our results suggest that 21.50 km2 and 34.70 km2 glacier area was lost from the region during the period 1976–2013 and 1976–2020 respectively. Besides this, out of the 106 High Altitude Glacial Lakes (HAGLs) found at an altitude of 4500 m above mean sea level (amsl), 14 potential spots are identified which can be a reason for future calamities. Our analysis of snow cover extents for the decade 2010–2021 suggests a considerable decrease of (16–28%) in winter snow cover. The unpredictable temperature fluctuations especially during the last few decades have also affected the freezing and thawing processes in the high-altitude areas. The changing behavior of the weathering processes quite often results in landslides, a major reason for disasters in the higher Himalaya. There is, thus, an urgent need to identify the high-risk sites in higher Himalaya which may be potential zones for future landslides. In anticipation to mitigate the resulting damages, the study emphasizes developing an early warning system based on geospatial technology to minimize loss of life, particularly for the workers employed in the engineering projects in the vicinity of the risk zone.

Glacier inventory and recent variations of Santa Inés Icefield, Southern Patagonia

ABSTRACT The study of glaciers in remote regions improves our understanding of global glacier change. With an area of 149.31 ± 1.84 km2, the Santa Inés Icefield constitutes one of the largest and least studied and explored glaciated areas of Southern Patagonia. We study the extent and glacier variations of the Santa Inés Icefield over the last 75 years, and we generate the most detailed glacier inventory to date of its 24 constituting glaciers. We estimate surface elevation changes between 2000 and 2014 using Shuttle Radar Topography Mission (SRTM) and TanDEM-X digital elevation models. Our results show a generalized trend of retreat, with a glacier area loss of −9.78 ± 1.52 km2 between 1998 and 2020, with annual rate increase from −0.15 ± 0.01 km2 a−1 (1998–2005) to −0.58 ± 0.10 km2 a−1 (2005–2020), and an average thinning of 0.60 ± 0.26 m a−1 (2σ) between 2000 and 2014. No clear correlation was found between retreat or thinning rates and Accumulation Area Ratio (AAR), terminus slope, aspect, or glacier type. While ERA5 reanalysis data shows no significant climatic trends in temperature or precipitation, a small warming trend below our detection record is the most likely cause of the observed retreat and thinning of the Santa Inés Icefield.

Tree-Ring Isotopic Records Suggest Seasonal Importance of Moisture Dynamics Over Glacial Valleys of the Central Himalaya

Accelerated glacier mass loss is primarily attributed to greenhouse-induced global warming. Land–climate interactions have increasingly been recognized as an important forcing at the regional-local scale, but the related effects on the Himalayan glaciers are less explored and thought to be an important factor regulating spatial heterogeneity. The aim of the present study is a multi-decadal approximation of glacier—hydroclimate interaction over the western region of the central Himalaya (WCH). Multi-species, highly coherent, tree-ring cellulose δ18O chronologies from three sites across the WCH were used to derive atmospheric humidity (Atmospheric Moisture Content: AMC) record of the last four centuries. Annual-scale AMC reconstruction implies a decreasing regional atmospheric moisture since the mid-19th century and a sharp decline in recent decades (1960s). Coherency analyses between regional AMC and glacier mass balance (GMB) indicate an abrupt phase-shift in the relationship after the 1960s within a common record of the last 273 years. To ascertain the cause of this phase-shift, annual AMC was disintegrated into seasonal-scale, utilizing ∼200 years of δ18O record of a deciduous tree species. Seasonal (winter: October–March; summer: April–September) AMC reconstructions and disaggregation results indicate higher sensitivity of regional ice-mass variability to winter moisture dynamics than summer.Winter season AMC reconstruction confirms a revival of winter westerlies-driven moisture influx in the region since the 1970 s. Meanwhile, the record for the summer season AMC indicates a gradual decline in moisture influx from the beginning of the 20th century. Interestingly, despite a prominent decline in Indian summer monsoon (ISM) precipitation after the mid-20th century, the summer season AMC—GMB relation remained stable. We hypothesize that decadal-scale greening, and consequently increased evapotranspiration and pre-monsoon precipitation might have been recycled through the summer season, to compensate for the ISM part of precipitation. However, isotope-enabled ecophysiological models and measurements would strengthen this hypothesis. In addition, high-resolution radiative forcing and long-term vegetation greening trends point towards a probable influence of valley greening on GMB. Our results indicate that attribution of ice mass to large-scale dynamics is likely to be modulated by local vegetation changes. This study contributes to the understanding of long-term hydroclimate—ice mass variability in the central Himalaya, where predictions are crucial for managing water resources and ecosystems.

Does the Recent Revival of Western Disturbances Govern the Karakoram Anomaly?

Abstract The global retreat in glaciers is considered to be one of the critical indicators of climate change. However, the glaciers of the Karakoram (KR) region of the Karakoram–Himalayas (KH) stand out because of their divergent response, displaying a surge as opposed to glaciers in other regions. This phenomenon is known as the “Karakoram anomaly.” Although many factors control the establishment and sustenance of the anomaly, the present study establishes winter precipitation associated with western disturbances (WDs) over the KH as one of the key drivers behind its emergence. To examine the role of WDs, a tracking algorithm is applied to 39 seasons (November–March) for three separate (ERA5, MERRA-2, and NCEP-CFSR/CFSv2) reanalysis datasets. The associated reanalysis ensemble statistics of WD properties produced in terms of their intensity, precipitation/snowfall volumes, and wind speed suggest a revival in recent years over the core-anomaly regions. However, the frequency has remained steady. The Karakoram has witnessed a rise of ∼10% in precipitation intensity associated with WDs in recent decades. The high percentage of snowfall received by the Karakoram (∼65%) from WDs relative to the total seasonal snowfall suggests a crucial role in modulating the regional mass-balance anomaly. Simultaneously, the amount of snowfall from non-WD sources in the Karakoram has had a statistically significant decline of ∼17% in recent decades, coinciding with the anomaly period. The enhanced intensity of WDs is found to be associated with changes in increased baroclinic instability and a shift of the subtropical westerly jet mean latitudinal position.

Late Quaternary geomorphic evolution of Teesta-Khangtse basin, north Sikkim

Quaternary climate change in eastern Himalaya is evidenced by a variety of glacial and fluvial landforms. In eastern Himalaya, the Teesta Khangtse glacier region located in the North District, Sikkim, has preserved many glacial and glacio-fluvial geomorphic features. The Optically stimulated luminescence (OSL) geochronology of lateral, recessional and ground moraines has provided proper evidence of episodic deglaciation and corresponding landform evolution of the region. The field disposition ground moraines exhibit the existence of a vast glacier system before 52 ka and successive different stages of its recession in the Late Quaternary time. The thinning of the glacier system laid down a thick cover of the ground moraine. Data show that the major recession of the Teesta glacier system took place in the Upper Pleistocene at around 52 ± 3 ka. This was followed by many episodic deglaciations between 11.4 and 1.4 ka. The recessional phase, close to the beginning of the Meghalayan stages of Holocene at 3.4 ± 0.2 ka, has been marked by fluvial and aeolian activities.

Intermediate ocean circulation and cryosphere dynamics in the northeast Atlantic during Heinrich Stadials: benthic foraminiferal assemblage response

AbstractThe interaction between ocean circulation and ice‐sheet dynamics plays a key role in the Quaternary climate. Compared with the surface and deep regions of the Atlantic Meridional Overturning Circulation (AMOC), the study of intermediate depths during key time periods, such as Heinrich Stadials (HSs), remains poorly documented, especially for the northeast Atlantic. Here we use benthic foraminiferal assemblage data to trace palaeoenvironmental changes from ~32 to 14 ka cal bp at ~1000 m depth in the Bay of Biscay. Our results highlight the high sensitivity of foraminifera, with species‐specific responses, to continental (European Ice Sheet dynamics) and marine (AMOC) forcing factors during the last three HSs. In general, HSs were characterised by the concomitant presence of meso‐oligotrophic and anoxia indicator species and the low abundance of high‐energy indicator species. This confirms an overall sluggish intermediate circulation during the three HSs in the northeast Atlantic. HS1 is distinctive for its abundance of high‐organic flux indicator species during its early phase. This is consistent with the fact that HS1 was by far the most important period of ice‐sheet retreat and meltwater release into the ocean over the studied time interval. Finally, foraminifera depict the mid‐HS2 reventilation event due to regional glacier instabilities.

Glacial runoff buffers droughts through the 21st century

Abstract. Global climate model projections suggest that 21st century climate change will bring significant drying in the terrestrial midlatitudes. Recent glacier modeling suggests that runoff from glaciers will continue to provide substantial freshwater in many drainage basins, though the supply will generally diminish throughout the century. In the absence of dynamic glacier ice within global climate models (GCMs), a comprehensive picture of future hydrological drought conditions in glaciated regions has been elusive. Here, we leverage the results of existing GCM simulations and a global glacier model to evaluate glacial buffering of droughts in the Standardized Precipitation-Evapotranspiration Index (SPEI). We compute one baseline version of the SPEI and one version modified to account for glacial runoff changing over time, and we compare the two for each of 56 large-scale glaciated basins worldwide. We find that accounting for glacial runoff tends to increase the multi-model ensemble mean SPEI and reduce drought frequency and severity, even in basins with relatively little (<2 %) glacier cover. When glacial runoff is included in the SPEI, the number of droughts is reduced in 40 of 56 basins and the average drought severity is reduced in 53 of 56 basins, with similar counts in each time period we study. Glacial drought buffering persists even as glacial runoff is projected to decline through the 21st century. Results are similar under representative concentration pathway (RCP) 4.5 and 8.5 emissions scenarios, though results for the higher-emissions RCP 8.5 scenario show wider multi-model spread (uncertainty) and greater incidence of decreasing buffering later in the century. A k-means clustering analysis shows that glacial drought buffering is strongest in moderately glaciated, arid basins.

Multi-Proxy analysis in the Gangotri Glacier region, Garhwal Himalaya: Glacial Stratigraphy and the overview of snout retreat, geomorphic evolution, and palaeoclimate signatures

Multi-Proxy analysis in the Gangotri Glacier region, Garhwal Himalaya: Glacial Stratigraphy and the overview of snout retreat, geomorphic evolution, and palaeoclimate signatures