Individual Glaciers Research Articles

Rock glacier composition and structure from radio wave speed analysis with dipping reflector correction

AbstractWe assess the composition and geometry of four individual rock glaciers in Alaska, Wyoming and Colorado by measuring their radio wave speed and applying these results to ground-penetrating radar depth corrections and dielectric mixing models. Our method includes a correction for subsurface reflector dip angle, which we show can lead to an incorrect determination of wave speeds using common midpoint configurations. By observing the radar properties of the rock glaciers and their supraglacial debris, we find that some of the sites exhibit nearly pure ice cores, and all of the sites indicate volumetric ice fractions >50%. These results have implications for terrestrial glaciology and hydrology because the present ice volume is connected to past ice accumulation and subsurface ice preservation, which may affect the future availability of alpine water resources. An understanding of the processes that govern rock glacier evolution over a wide range of latitudes and elevations will also contribute to the exploration of planetary surfaces such as Mars, which hosts a significant population of debris-covered glaciers. Our subsurface composition and geometry estimates will inform simulations of rock glacier formation and evolution to test hypothesized ice origin mechanisms along with the preservation of climate signals.

Long-term records of glacier evolution and associated proglacial lakes on the Tibetan Plateau (1976‒2020)

ABSTRACT The glaciers on the Tibetan Plateau (TP) constitute critical sources of water for the proglacial lakes and many rivers found downstream. To better understand the evolution of glaciers and the impact of this on proglacial lakes, seven glaciers corresponding to continenṅtal, subcontinental, and marine climate types that are influenced by westerlies and the Indian summer monsoon were selected for study. The evolution of the edges of these glaciers and their associated proglacial lakes were identified based on the visual interpretation of Landsat TM/ETM+/OLI images. A dataset covering the period 1976–2020 that included the glacier and proglacial lake edge vectors was then created. The relative errors in the areas of the individual glaciers were less than 3%, and for the proglacial lakes these errors were in the range 0%–7%. The dataset was used to effectively compare the changes in glaciers and proglacial lakes that have occurred over the past four decades. The most striking changes that were found were the retreat of glaciers and the formation of small proglacial lakes. This dataset could also be used as a proxy to support research on changes in mountain glaciers, particularly their response to climate change and water resources. This response is of great scientific significance and is important in many applications, including assessments of the ecological problems caused by melting glaciers. The dataset can be downloaded from http://doi.org/10.57760/sciencedb.j00076.00131.

Estimating glacier mass balance in High Mountain Asia based on Moderate Resolution Imaging Spectroradiometer retrieved surface albedo from 2000 to 2020

AbstractGlacier surface albedo is a key parameter of the glacier mass and energy balance process. Many scholars have used the albedo method to study mass balance for an individual glacier, but less attention has been given to large‐area glaciers. Based on Moderate Resolution Imaging Spectroradiometer (MODIS) retrieved glacier surface albedo and in situ mass balance, the correlations between albedo and mass balance are reported. The minimum/mean method (the whole glacier albedo is calculated by averaging the minimum/mean albedo of each grid cell), the MODIS snow albedo products (MxD10A1) and the MCD43A3 shortwave albedo were tested during the melt season (June–August) for four glaciers in the High Mountain Asia (HMA). Results reveal that albedo is well correlated with mass balance, the correlation (r) ranging from 0.41 to 0.90. Overall, the minimum method is better than the mean method, and MxD10A1 is better than MCD43A3. The albedo changes were calculated based on the MxD10A1 and the mean method, and a linear relationship is established between albedo changes and digital elevation models (DEMs) calculated mass balance from 2000 to 2016. A strong linear correlation (r = .9) is found between albedo changes and mass balance while excluding some areas that have insignificant seasonal variation in albedo, and the reconstructed albedo–mass balance relationship can be used to retrieve mass balance in large‐scale glaciers. Furthermore, the average loss of mass from 2000 to 2020 is calculated as −0.225 ± 0.040 m w.e.a−1. The greatest glacier mass loss is concentrated in the southeastern part of HMA, the mass loss in the north and west is less than that in the southeast, and the glacier mass is in a state of aggravated loss in recent years. Our study also offers a new method for estimating the large‐scale glacier mass balance.

Advances in data availability to constrain and evaluate frontal ablation of ice-dynamical models of Greenland's tidewater peripheral glaciers

AbstractWe revise and evaluate frontal ablation fluxes obtained by the Open Global Glacier Model (OGGM) for Greenland's tidewater peripheral glaciers de-coupled from the ice sheet. By making use of new region-wide ice thickness and solid ice discharge data, we re-evaluate model performance and suggest future research directions to improve the ice thickness estimation of glacier models. OGGM is unable to predict individual tidewater glacier dynamics well if it has to rely only on surface mass balance estimates and the assumption of a closed budget to constrain the calving parameterization. Velocity observations are essential to constrain the model and estimate the dynamic mass loss of Greenland's tidewater peripheral glaciers.

Topographic modulation of outlet glaciers in Greenland: a review

AbstractBed topography is a critical parameter for determining the modern-day and future dynamics of ice sheets and their outlet glaciers. This is because the topography controls the state of stress for glaciers. At glacier termini, topography can influence the timing of terminus retreat by controlling access to warm ocean waters and/or by influencing the ability of a glacier terminus to retreat over bed bumps (moraines). Inland from the terminus, the topography can also influence where glacier retreat and thinning can stabilize. In part, this is because of knickpoints in bed topography created through glacial erosion that may influence the extent to which thinning can diffuse inland for an individual glacier and thus, the timing and magnitude of long-term mass loss. Here we provide a review of the current literature on these topics. While much of the reviewed literature assumes that topography is stable on relevant timescales to humans, new research suggests that topography may change much faster than previously thought and this further complicates our ability to project future outlet glacier change.

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.

Little Ice Age climate in southernmost Greenland inferred from quantitative geospatial analyses of alpine glacier reconstructions

Alpine glaciers are sensitive responders to climate fluctuations, especially to changes in summer temperature, and thus their past extents are invaluable indicators of past climate. Here, we leverage geomorphological evidence of past glacier extent to reconstruct the three-dimensional surfaces of 42 land-terminating paleoglaciers in southernmost Greenland and calculate their equilibrium-line altitudes (ELAs) during the presumed coldest interval of the Little Ice Age (LIA). We compare LIA paleoglacier ELAs with observed modern glacier ELAs (i.e. snowlines) to estimate the LIA summer temperature depression relative to present. On average, we find that ELAs rose 122 ± 64 m since the LIA, which corresponds to a summer temperature change of 1.1± 0.6 ° C, assuming no change in precipitation. Because there are minimal constraints on LIA precipitation anomalies in southernmost Greenland, we also report summer temperature changes for precipitation values ranging from a substantially drier to substantially wetter than modern LIA. When compared with independent temperature evidence, our results suggest LIA precipitation was similar to or slightly less than today. The alpine glaciers studied lost (on average) 56± 16% of their area and 44± 13% of their centerline length between the LIA culmination and 2019 CE. In general, smaller and lower elevation glaciers lost larger fractions of their area. We find no clear geographic patterns in the magnitudes of ELA, area, or length changes across the 9000 km2 study area despite its heterogeneous climate. This study demonstrates a workflow for regional-scale paleoglacier reconstruction and provides the first quantitative LIA summer paleotemperature estimate for southernmost Greenland via region-wide glacial evidence. Our work also suggests the need for reconstruction of a large number of glaciers to infer past regional climatic information, as individual glaciers may respond heterogeneously to climate perturbations leading to variable changes in their ELA and length.

Synchronous Retreat of Southeast Greenland's Peripheral Glaciers

AbstractRecently, scientific attention has focused on estimating Greenland's dynamic mass loss through changes to flow speeds, thickness, and length on its marine outlet glaciers. For the ice sheet outlet glaciers, dynamic mass loss has been found to be highly sensitive to changes in climate and individual glacier geometry. For the ice‐sheet‐independent marine glaciers around Greenland's periphery, dynamic mass loss is presently overlooked. Here, we apply an open‐source, automated method of measuring glacier length changes using satellite imagery, to produce highly detailed records of length changes for 135 peripheral marine glaciers in southeast Greenland. We find evidence for anomalous retreat across 56 glaciers coincident with elevated surface melt in 2016, with melt 22% above the 2013–2019 average. Our detailed observations resolve the widespread, rapid, and synchronous response of these independent marine glaciers to increased meltwater input in 2016, indicating that their dynamics may be more sensitive to atmospheric warming than currently thought.

Chlorine-36 Surface Exposure Dating of Late Holocene Moraines and Glacial Mass Balance Modeling, Monte Sierra Nevada, South-Central Chilean Andes (38°S)

The development of robust chronologies of Neoglaciation from individual glaciers throughout the high-altitude Andes can provide fundamental knowledge of influences such as regional temperature and precipitation variability, and aid in predicting future changes in the Andean climate system. However, records of Late Holocene glaciation from the Central Chilean Andes are sparse, and often poorly constrained. Here, we present 36Cl surface exposure ages, dendrochronologic constraints, and glacial mass balance modeling simulations of Late Holocene glacier fluctuations in the Central-South Chilean Andes. A series of concentric moraine ridges were identified on Monte Sierra Nevada (38°S), where exposure dating of basaltic boulders was used to establish a chronology of ice recession. We infer that moraine abandonment of the most distal ridge in the valley commenced by ∼4.2 ka, and was followed by glacier margin retreat to an up-valley position. Exposure ages of the oldest Late Holocene boulders (∼2.5–0.8 ka) along the marginal extents of the moraine complex indicate fluctuations of the glacier terminus prior to ∼0.65 ka. A final expansion of the ice margin reoccupied the position of the 4.2 ka moraine, with abatement from the outermost composite moraine occurring by ∼0.70 ka, as constrained by tree-ring data from live Araucaria araucana trees. Finally, a series of nested moraines dating to ∼0.45–0.30 ka, formed from a pulsed ice recession during the latest Holocene when the lower reaches of the glacial snout was most likely debris mantled. A distributed temperature index model combined with a glacier flow model was used to quantify an envelope of possible climatic conditions of Late Holocene glaciation. The glacial modeling results suggest conditions were ∼1.5°C colder and 20% wetter during peak Neoglaciation relative to modern conditions. These records also suggest a near-coeval record of Late Holocene climate variability between the middle and high southern latitudes. Furthermore, this study presents some of the youngest 36Cl exposure ages reported for moraines in the Andes, further supporting this method as a valuable geochronologic tool for assessing Late Holocene landscape development.

High spatial and temporal variability in Antarctic ice discharge linked to ice shelf buttressing and bed geometry

Antarctica’s contribution to global mean sea level rise has been driven by an increase in ice discharge into the oceans. The rate of change and the mechanisms that drive variability in ice discharge are therefore important to consider in the context of projected future warming. Here, we report observations of both decadal trends and inter-annual variability in ice discharge across the Antarctic Ice Sheet at a variety of spatial scales that range from large drainage basins to individual outlet glacier catchments. Overall, we find a 37 ± 11 Gt year−1 increase in discharge between 1999 and 2010, but a much smaller increase of 4 ± 8 Gt year−1 between 2010 and 2018. Furthermore, comparisons reveal that neighbouring outlet glaciers can behave synchronously, but others show opposing trends, despite their close proximity. We link this spatial and temporal variability to changes in ice shelf buttressing and the modulating effect of local glacier geometry.

Unravelling the long-term, locally heterogenous response of Greenland glaciers observed in archival photography

Abstract. We present an approach for extracting quantifiable information from archival aerial photographs to extend the temporal record of change over a region of the central eastern Greenland Ice Sheet. The photographs we use were gathered in the 1930s as part of a surveying expedition, and so they were not acquired with photogrammetric analysis in mind. Nevertheless, we are able to make opportunistic use of this imagery, as well as additional, novel datasets, to explore changes at ice margins well before the advent of conventional satellite technology. The insights that a longer record of ice margin change bring is crucial for improving our understanding of how glaciers are responding to the changing climate. In addition, our work focuses on a series of relatively small and little studied outlet glaciers from the eastern margin of the ice sheet. We show that whilst air and sea surface temperatures are important controls on the rates at which these ice masses change, there is also significant heterogeneity in their responses, with non-climatic controls (such as the role of bathymetry in front of calving margins) being extremely important. In general, there is often a tendency to focus either on changes of the Greenland Ice Sheet as a whole, or on regional variations. Here, we suggest that even this approach masks important variability, and full understanding of the behaviour and response of the ice sheet requires us to consider changes that are taking place at the scale of individual glaciers.

Pan-Alpine glacier phenology reveals lowering albedo and increase in ablation season length

Glaciers in many parts of the world are reported to be undergoing a darkening process (decrease in surface albedo). This has multiple causes, including the presence of impurities (such as mineral dust, carbonaceous particles, algae and cryoconite), and debris. Also glacier melt can induce an albedo decrease by initiating a melt-albedo feedback cycle. The extent of this albedo decrease and its spatial variability in different mountain ranges however are poorly known. In this study, we assess albedo changes on a selection of Alpine glaciers (542 glaciers >0.1 km2) by deriving eight albedo metrics from MODIS MOD10A1 satellite observations over a time period of 20 years (2000–2019). Albedo metrics include the start and end of the ablation season and its length, calculated through the selection of a threshold (albedo = 0.4) to separate melting ice from snow. We further calculated the number of ice melt days, integral of the length of the ablation season, minimum annual albedo, mean summer albedo and mean annual albedo. We identified significant trends in all metrics for a large percentage of glacier cells. A negative trend in minimum albedo (−0.06 decade−1 on average) was identified for 56% of glacier cells, and 70% of glaciers; a positive trend in the length of season (+18 days decade−1 on average) was identified for 11% of glacier cells and 19% of glaciers. Changes in minimum albedo occur mostly around the glacier median elevation, while for other metrics (e.g. start and length of season) changes are more frequent at the glacier termini (i.e. below 25th elevation percentile). We further investigated the relationship between the metrics and climate (downscaled ERA5 reanalysis data) and topographic (ALOS AW3D30 DEM) variability; we found that average summer temperature and elevation are the most significant proxies for all metrics (maximum correlation = 0.40 between elevation and minimum albedo) compared to spring temperature and other topographic variables. Finally, we looked at the ability of the albedo metrics to represent annual and summertime glacier mass balance of 31 selected Alpine glaciers in the World Glacier Monitoring Service database, finding significant correlations between minimum and summertime albedo and annual mass balance (R2 = 0.44 for minimum albedo and 0.40 for summertime albedo using all observations). Considering individual glaciers, all showed significant correlations with minimum albedo, and some of them are strongly correlated (e.g. Argentiere: R2 = 0.84, Saint Sorlin R2 = 0.88). Our glacier phenology approach opens new perspectives for the remote sensing of alpine and polar glaciers.

Ice‐Dynamical Glacier Evolution Modeling—A Review

AbstractGlaciers play a crucial role in the Earth System: they are important water suppliers to lower‐lying areas during hot and dry periods, and they are major contributors to the observed present‐day sea‐level rise. Glaciers can also act as a source of natural hazards and have a major touristic value. Given their societal importance, there is large scientific interest in better understanding and accurately simulating the temporal evolution of glaciers, both in the past and in the future. Here, we give an overview of the state of the art of simulating the evolution of individual glaciers over decadal to centennial time scales with ice‐dynamical models. We hereby highlight recent advances in the field and emphasize how these go hand‐in‐hand with an increasing availability of on‐site and remotely sensed observations. We also focus on the gap between simplified studies that use parameterizations, typically used for regional and global projections, and detailed assessments for individual glaciers, and explain how recent advances now allow including ice dynamics when modeling glaciers at larger spatial scales. Finally, we provide concrete recommendations concerning the steps and factors to be considered when modeling the evolution of glaciers. We suggest paying particular attention to the model initialization, analyzing how related uncertainties in model input influence the modeled glacier evolution and strongly recommend evaluating the simulated glacier evolution against independent data.

The Spatiotemporal Change of Glacier Runoff Is Comparably Attributed to Climatic Factors and Physical Properties in Northwestern China

The spatiotemporal regimes of glacier runoff (GR) under a warming climate are of great concern, especially in dryland areas in northwestern China (DAC). Due to the difficulty of observing GR, little attention has been given to the spatiotemporal change in GR at regional scales. This study uses the regional individual glacier mass balance (GMB) dataset developed by digital elevation models (DEMs) to simulate the spatiotemporal regime of GR using atmospheric parameters considering both ablation and accumulation processes on glaciers. In this study, GR, including glacier meltwater runoff (MR) and delayed water runoff (DR) of the DAC, was quantitatively assessed at a catchment scale from 1961 to 2015. The total annual GR in the DAC was (100.81 ± 68.71) × 108 m3 in 1961–2015, where MR accounted for 68%. Most basins had continuously increasing tendencies of different magnitudes from 1961 to 2015. The least absolute shrinkage and selection operator (LASSO) and random forest techniques were used to explore the contributions of climate factors and glacier physical properties to GR, and the results indicated that climate factors could explain 56.64% of the variation. In comparison, the remaining 43.36% could be explained by the physical properties of glaciers themselves (i.e., degree-day factor on ice, degree-day factor on snow, glacier median height, aspect, and slope). This study not only improves our understanding of the spatiotemporal change in GR in the drylands of northwestern China at spatial and temporal resolutions but also highlights the role of physical properties in explaining the heterogeneous dynamics among GRs unlike previous studies that only emphasize rising temperatures.

Modelling supraglacial debris-cover evolution from the single-glacier to the regional scale: an application to High Mountain Asia

Abstract. Currently, about 12 %–13 % of High Mountain Asia’s glacier area is debris-covered, which alters its surface mass balance. However, in regional-scale modelling approaches, debris-covered glaciers are typically treated as clean-ice glaciers, leading to a bias when modelling their future evolution. Here, we present a new approach for modelling debris area and thickness evolution, applicable from single glaciers to the global scale. We derive a parameterization and implement it as a module into the Global Glacier Evolution Model (GloGEMflow), a combined mass-balance ice-flow model. The module is initialized with both glacier-specific observations of the debris' spatial distribution and estimates of debris thickness. These data sets account for the fact that debris can either enhance or reduce surface melt depending on thickness. Our model approach also enables representing the spatiotemporal evolution of debris extent and thickness. We calibrate and evaluate the module on a selected subset of glaciers and apply GloGEMflow using different climate scenarios to project the future evolution of all glaciers in High Mountain Asia until 2100. Explicitly accounting for debris cover has only a minor effect on the projected mass loss, which is in line with previous projections. Despite this small effect, we argue that the improved process representation is of added value when aiming at capturing intra-glacier scales, i.e. spatial mass-balance distribution. Depending on the climate scenario, the mean debris-cover fraction is expected to increase, while mean debris thickness is projected to show only minor changes, although large local thickening is expected. To isolate the influence of explicitly accounting for supraglacial debris cover, we re-compute glacier evolution without the debris-cover module. We show that glacier geometry, area, volume, and flow velocity evolve differently, especially at the level of individual glaciers. This highlights the importance of accounting for debris cover and its spatiotemporal evolution when projecting future glacier changes.

Recent Evolution of Glaciers in the Manaslu Region of Nepal From Satellite Imagery and UAV Data (1970–2019)

Glacierized mountain ranges such as the Himalaya comprise a variety of glacier types, including clean and debris-covered glaciers. Monitoring their behaviour over time requires an assessment of changes in area and elevation along with surface features and geomorphology. In this paper we quantify the surface evolution of glacier systems in the Manaslu region of Nepal over the last five decades using 2013/2019 multi-sensor imagery and elevation data constructed from 1970 declassified Corona imagery and 1970 declassified Corona imagery. We investigate area changes, glacier thickness, geodetic glacier mass balance and surface velocity changes at regional scales and focus on the Ponkar Glacier and Thulagi Glacier and Lake for an in-depth assessment of surface geomorphology and surface feature dynamics (ponds, vegetation and ice cliffs). The time series of surface elevation changes for the lower ablation area of Ponkar Glacier is extended using 2019 UAV-based imagery and field-based ablation rates measured over the period 2016–2019. Glaciers in the Manaslu region experienced a mean area loss of −0.26 ± 0.0001% a−1 between 1970 and 2019. The mean surface lowering was −0.20 ± 0.02 ma−1 over the period 1970 to 2013, corresponding to a regional geodetic mass balance of −0.17 ± 0.03 m w. e.a−1. Overall, debris-covered glaciers had slightly higher thinning rates compared to clean ice glaciers; lake-terminating glaciers had double thinning rates compared to land-terminating glaciers. Individual glacier mass balance was negatively controlled by glacier slope and mean glacier elevation. During the period 1970 to 2013, Ponkar Glacier had a geodetic mass balance of −0.06 ± 0.01 m w. e.a−1, inversely correlated with parts of the central trunk thickening. Between 2013 and 2019 there was a nine-fold increase in the thinning rates over the lower parts of the glacier tongue relative to the period 1970–2013. Ice-surface morphology changes between 1970 and 2019 on Ponkar Glacier include a decrease in ogives and open crevasses, an increase in ice cliffs and ponds and the expansion of the supraglacial debris and ice-surface vegetation. These changes point to reduced ice-dynamic activity and are commensurate with the observed recession and negative glacier mass balance over the last five decades.

A reconstruction of Jostedalsbreen during the Little Ice Age and geometric changes to outlet glaciers since then

Mountain glaciers and ice caps are undergoing rapid mass loss but rates of present-day changes and models of future projections both lack long-term (centennial-scale) context. Here, we reconstruct the maximum glacier extent and ice surface of Jostedalsbreen, which is the largest ice mass in mainland Europe, during the Little Ice Age (LIA) ∼ 1740 to 1860. The LIA maximum ice-covered area was 568 km2 and the LIA ice volume was between 61 km3 and 91 km3. We show that the major outlet glaciers have lost at least 110 km2 or 19% of their LIA area and 14 km3 or 18% of their LIA volume until 2006. The largest proportional changes for individual outlet glaciers are associated with the loss of ice falls and consequent disconnection of tributaries. Glacier-specific hypsometry changes suggest a mean rise in ELA of 135 m but there is wide inter-glacier variability. A median date for the LIA of 1755 suggests that the long-term rate of ice mass loss has been 0.05 m w.e. a−1. That long-term rate is virtually the same as modern rates, which contrasts with findings of other studies around the world reporting acceleration of glacier mass loss rates since the LIA. Overall, we highlight the utility of geomorphological-based reconstructions of glaciers for understanding and quantifying long-term (centennial-scale) responses to climate and hence for understanding of meltwater production and proglacial landscape evolution.

Quantifying Geodetic Mass Balance of the Northern and Southern Patagonian Icefields Since 1976

Southern Andean glaciers contribute substantially to global sea-level rise. Unfortunately, mass balance estimates prior to 2000 are limited, hindering our understanding of the evolution of glacier mass changes over time. Elevation changes over 1976/1979 to 2000 derived from historical KH-9 Hexagon imagery and NASADEM provide the basis for geodetic mass balance estimates for subsets of the Northern Patagonian Icefield (NPI) and the Southern Patagonian Icefield (SPI), extending current mass balance observations by ∼20 years. Geodetic mass balances were −0.63 ± 0.03 m w.e. yr−1 for 63% of the NPI and −0.33 ± 0.05 m w.e. yr−1 for 52% of the SPI glacierized areas for this historical period. We also extend previous estimates temporally by 25% using NASADEM and ASTER elevation trends for the period 2000 to 2020, and find geodetic mass balances of −0.86 ± 0.03 m w.e. yr−1 for 100% of the NPI and −1.23 ± 0.04 m w.e. yr−1 for 97% of the SPI glacierized areas. 2000–2020 aggregations for the same areas represented in the 1976/1979 to 2000 estimates are −0.78 ± 0.03 m w.e. yr−1 in the NPI and −0.80 ± 0.04 m w.e. yr−1 on the SPI. The significant difference in SPI geodetic mass balance in the modern period for 100% vs. 52% of the glacierized area suggests subsampling leads to significant biases in regional mass balance estimates. When we compare the same areas in each time period, the results highlight an acceleration of ice loss by a factor of 1.2 on the NPI and 2.4 on the SPI in the 21st century as compared to the 1976/1979 to 2000 period. While lake-terminating glaciers show the most significant increase in mass loss rate from 1976/1979–2000 to 2000–2020, mass balance trends are highly variable within glaciers of all terminus environments, which suggests that individual glacier sensitivity to climate change is dependent on a multitude of morphological and climatological factors.

An inventory of Norway's glaciers and ice-marginal lakes from 2018–19 Sentinel-2 data

AbstractWe used Sentinel-2 satellite imagery at 10 m resolution to map the extent of Norway's glaciers and ice-marginal lakes over 2018–19. We applied a standardized semi-automated band ratio method to derive glacier outlines and ice-marginal lakes. To optimise the results, we manually edited the ice-lake interfaces, debris, snow and parts of the glaciers situated under shadow. We compared our Sentinel-2 derived outlines with very high-resolution aerial orthophotos and Pléiades satellite orthoimages. Glaciers larger than 0.3 km2have area differences within 7%, whereas values are larger for smaller glaciers. The orthophotos and orthoimages provide more details and a higher mapping accuracy for individual glaciers, but require manual digitisation, have smaller spatial and temporal coverage and can have adverse snow conditions. We found a total glacier area of 2328 ± 70 km2of which the ten largest glaciers accounted for 52%. The glacier area decreased 15% since the previous inventory (Landsat data from 1999 to 2006), the reduction being largest in northern Norway (22%) compared to southern Norway (10%). We detected more than 2000 previously undetected smaller glaciers and ice patches (covering 37 km2) and 360 new ice-marginal lakes.

Long‐term spatiotemporal variability in the surface velocity of Eastern Himalayan glaciers, India

AbstractInvestigation of spatiotemporal variation in glacier velocity is imperative to comprehend glacier mass and volume loss as a function of their sensitivity to climate change. The long‐term glacier velocity record for the Eastern Himalayan region is of utmost importance owing to its data scarcity and climate sensitivity. Here, we present a long‐term dataset spanning more than two decades (1994–2020) of glacier surface velocity for the entire Sikkim Himalaya by applying image correlation methods on the multi‐temporal Landsat images. Our results demonstrate an average glacier surface velocity decline from 15.7 ± 5.69 (1994/96) to 12.88 ± 2.09 m yr−1 (2018/2020), that is a decline of ~15% during the period of investigation. Trend analysis shows a decreasing trend in median velocity (32.2%) at a rate of 0.25 m yr−1. Despite the general decline in average glacier velocity, the rate of slowdown of individual glaciers is extremely heterogeneous (3.6–20 m yr−1). Our study shows that up to 32% of the observed heterogeneity in velocity variation can be explained by the variation in glacier size. The present study highlights that large glaciers with thick ice cover move faster compared to small glaciers (even those situated on steep slopes). The findings are significant and have direct implications for assessing future water availability scenarios and modelling glacio‐hydrology in the region.