Mass Balance Of Mountain Glaciers Research Articles

Asynchronous glacial dynamics of Last Glacial Maximum mountain glaciers in the Ikh Bogd Massif, Gobi Altai mountain range, southwestern Mongolia: aspect control on glacier mass balance

Abstract. Mountain glacier mass balance is affected by factors other than climate, such as topography, slope, and aspect. In midlatitude high-mountain regions, the north–south aspect contrast can cause significant changes in insolation and melt, resulting in local asynchrony in glacial dynamics. This study documents the asynchronous response of two paleoglaciers in southwestern Mongolia to the local topoclimatic factors using 10Be exposure age dating and 2D ice surface modeling. 10Be surface exposure age dating revealed that the Ikh Artsan south-facing valley glacier culminated (MIA1) at 20.1 ± 0.7 ka, coinciding with the global Last Glacial Maximum (gLGM). In contrast, the north-facing Jargalant paleoglacier (MJ1) culminated at 17.2 ± 1.5 ka, around Heinrich Stadial 1 and during the post-gLGM Northern Hemisphere warming. Our temperature-index melt model predicts that ablation will be substantially lower on the north-facing slope, as it is exposed to less solar radiation and cooler temperatures than the south-facing slope. The 2D ice surface modeling also revealed that the south-facing Ikh Artsan Glacier abruptly retreated from its maximum extent at 20 ka, but the Jargalant Glacier on the shaded slope consistently advanced and thickened due to reduced melt until 17 ka. The timing of the modeled glacier culmination is consistent within ± 1σ of the 10Be exposure age results. Extremely old ages ranging from 636.2 to 35.9 ka were measured for the inner moraines in the Jargalant cirque (MJ2–MJ4), suggesting a problem with inheritance from boulders eroded from the summit plateau.

Energy and glacier mass balance of Fürkeleferner, Italy: past, present, and future

The energy and mass balance of mountain glaciers translate into volume changes that play out as area changes over time. From this, together with former moraines during maximum advances, information on past climate conditions and the climatic drivers behind during glacier advances can be obtained. Here, we use the distributed COupled Snowpack and Ice surface energy and mass balance model in PYthon (COSIPY) to simulate the present state of an Italian glacier, named Fürkeleferner, for the mass balance years 2013–2017. Next, we investigate the local climate during the time of the last “Little Ice Age” (LIA) maximum glacier advance using COSIPY together with the LIA glacier outline retrieved from moraine mapping and a digital elevation model (DEM) adapted for the glacier’s geometry at the time of the LIA as a benchmark. Furthermore, the glacier’s sensitivity to future air temperature increase of +1 K and +2 K is investigated using the same model. For all simulations, meteorological data of closely located climate stations are used to force the model. We show the individual monthly contribution of individual energy and mass balance components. Refreezing during the summer months is an important component of the energy and mass balance, on average about 9 % relative to total annual ablation. The results from simulating past climate show a 2.8 times larger glacier area for Fürkeleferner during the LIA than today. This further implies a 2.5 K colder climate, assuming that the amount of precipitation was 10 %–20 % in excess of today’s value. Concerning further temperature increase of 2 K, the glacier would only consist of the ablation area implying sustained mass loss and eventual total mass loss. Even under current climatic conditions, the glacier area would have to decrease to 17 % of its current area to be in a steady state. We discuss the reliability of the results by comparing simulated present mass balance to measured mass balances of neighboring glaciers in the European Alps and with short-term measurements on Fürkeleferner itself. In conclusion, we are able to show how the glacier responds to past and future climate change and determine the climatic drivers behind.

Large‐eddy simulations of the atmospheric boundary layer over an Alpine glacier: Impact of synoptic flow direction and governing processes

AbstractThe mass balance of mountain glaciers is of interest for several applications (e.g., local hydrology or climate projections), and turbulent fluxes can be an important contributor to glacier surface mass balance during strong melting events. The underlying complex terrain leads to spatial heterogeneity and non‐stationarity of turbulent fluxes. Owing to the contribution of thermally induced flows and gravity waves, exchange mechanisms are fully three‐dimensional, instead of only vertical. Additionally, glaciers have their own distinct microclimate, governed by a down‐glacier katabatic wind, which protects the glacier ice and interacts with the surrounding flows on multiple scales. In this study, we perform large‐eddy simulations with the Weather Research and Forecasting model at a horizontal grid spacing of 48 m to gain insight into the boundary‐layer processes over an Alpine valley glacier, the Hintereisferner. We choose two case studies from the Hintereisferner experiment measurement campaign with different synoptic wind directions (southwest and northwest). Model evaluation with an array of eddy‐covariance stations on the glacier tongue and surroundings reveals that the Weather Research and Forecasting model is able to simulate the general glacier boundary‐layer structure. Under a southwesterly airflow, the down‐glacier wind is supported by the synoptic wind parallel to the glacier axis, a stable boundary layer is present over the ice surface, and local processes govern the turbulence kinetic energy production. Under northwesterly airflow, a cross‐glacier valley flow and a breaking gravity wave lead to strong turbulent mixing and to the subsequent erosion of the glacier boundary layer. Stationarity analysis of the sensible heat flux suggests non‐stationary behaviour for both case study days, whereas non‐stationarity is highest on the northwesterly day during the gravity‐wave event. These results suggest that the synoptic wind direction has, in addition to upstream topography and the atmospheric stability, a strong impact on whether a local glacier boundary layer can form or not, influencing whether a glacier is able to maintain its own microclimate.

Glacier albedo reduction and drought effects in the extratropical Andes, 1986–2020

AbstractSurface albedo typically dominates the mass balance of mountain glaciers, though long-term trends and patterns of glacier albedo are seldom explored. We calculated broadband shortwave albedo for glaciers in the central Chilean Andes (33–34°S) using end-of-summer Landsat scenes between 1986 and 2020. We found a high inter-annual variability of glacier-wide albedo that is largely a function of the glacier fractional snow-covered area and the total precipitation of the preceding hydrological year (up to 69% of the inter-annual variance explained). Under the 2010–2020 ‘Mega Drought’ period, the mean albedo, regionally averaged ranging from ~0.25–0.5, decreased by −0.05 on average relative to 1986–2009, with the greatest reduction occurring 3500–5000 m a.s.l. In 2020, differences relative to 1986–2009 were −0.14 on average as a result of near-complete absence of late summer snow cover and the driest hydrological year since the Landsat observation period began (~90% reduction of annual precipitation relative to the 1986–2009 period). We found statistically significant, negative trends in glacier ice albedo of up to −0.03 per decade, a trend that would have serious implications for the future water security of the region, because glacier ice melt acts to buffer streamflow shortages under severe drought conditions.

An optimized method to calculate the geodetic mass balance of mountain glaciers

ABSTRACTUnderstanding the effects of climate on glaciers requires precise estimates of ice volume change over several decades. This is achieved by the geodetic mass balance computed by two means: (1) the digital elevation model (DEM) comparison (SeqDEM) allows measurements over the entire glacier, however the low contrast over glacierized areas is an issue for the DEM generation through the photogrammetric techniques and (2) the profiling method (SePM) is a faster alternative but fails to capture the spatial variability of elevation changes. We present a new framework (SSD) that relies upon the spatial variability of the elevation change to densify a sampling network to optimize the surface-elevation change quantification. Our method was tested in two small glaciers over different periods. We conclude that the SePM overestimates the elevation change by ~20% with a mean difference of ~1.00 m (root mean square error (RMSE) = ~3.00 m) compared with results from the SeqDEM method. A variogram analysis of the elevation changes showed a mean difference of <0.10 m (RMSE = ~2.40 m) with SSD approach. A final assessment on the largest glacier in the French Alps confirms the high potential of our method to compute the geodetic mass balance, without going through the generation of a full-density DEM, but with a similar accuracy than the SeqDEM approach.

Model-based calculations of surface mass balance of mountain glaciers for the purpose of water consumption planning: focus on Djankuat Glacier (Central Caucasus)

Mountain glaciers act as regulators of run-off in the summer period, which is very crucial for economy especially in dynamically developing regions with rapidly growing population, such as Central Asia or the Northern Caucasus in Russia. In overall, glaciers stabilize water consumption in comparatively arid areas and provide conditions for sustainable development of the economy in mountainous regions and in the surrounding territories. A proper prediction of the glacial run-off is required to elaborate strategies of the regional development. This goal can be achieved by implementation of mathematical modeling methods into planning methodologies. In the paper, we consider one of the first steps in glacier dynamical modeling – surface mass balance simulation. We focus on the Djankuat Glacier in the Central Caucasus, where regular observations have been conducted during the last fifty years providing an exceptional opportunity to calibrate and to validate a mathematical model.

Relationship between glacier melting and atmospheric circulation in the southeast Siberia

The interaction between climate and cryosphere is a key issue in recent years. Changes in surface mass balance of mountain glaciers closely correspond to differential changes in atmospheric circulation. Mountain glaciers in southeast Siberia located on East Sayan, Baikalsky and Kodar ridges have been continuously shrinking since the end of the Little Ice Age. In this study we used daily synoptic weather maps (Irkutsk Center of Hydrometeorology and Environmental Monitoring), 500 hPa, 700 hPa and 850 hPa geopotential height and air temperature data of NCEP/NCAR reanalysis to assess relationships between atmospheric circulation patterns and the sum of positive temperature (SPT), a predictor of summer ice/snow ablation. Results show that increased SPT (ablation) is generally associated with anticyclones and anticyclonic pressure fields (with cloudless weather conditions) and warm atmospheric fronts. Decreased SPT (ablation) is strongly correlated with cyclones and cyclonic type pressure fields, cold atmospheric fronts and air advections. Significant correlations have been found between ablation and cyclonic/anticyclonic activity. Revealed decreasing trends in the SPT in three glaciarized ridges at the beginning of the 21st century led to changes of air temperature and snow/ice melt climates.

IMPROVEMENT OF DEM GENERATION FROM ASTER IMAGES USING SATELLITE JITTER ESTIMATION AND OPEN SOURCE IMPLEMENTATION

Abstract. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) system embarked on the Terra (EOS AM-1) satellite has been a source of stereoscopic images covering the whole globe at a 15m resolution at a consistent quality for over 15 years. The potential of this data in terms of geomorphological analysis and change detection in three dimensions is unrivaled and needs to be exploited. However, the quality of the DEMs and ortho-images currently delivered by NASA (ASTER DMO products) is often of insufficient quality for a number of applications such as mountain glacier mass balance. For this study, the use of Ground Control Points (GCPs) or of other ground truth was rejected due to the global “big data” type of processing that we hope to perform on the ASTER archive. We have therefore developed a tool to compute Rational Polynomial Coefficient (RPC) models from the ASTER metadata and a method improving the quality of the matching by identifying and correcting jitter induced cross-track parallax errors. Our method outputs more accurate DEMs with less unmatched areas and reduced overall noise. The algorithms were implemented in the open source photogrammetric library and software suite MicMac.

Multi-Decadal Changes in Glacial Parameters of the Fedchenko Glacier in Tajikistan

An accurate estimation of mass balance of mountain glaciers is important to understand global climate change process. The glaciers in the Pamir region are remote, difficult to access, and are often impossible to evaluate using in-situ methods. The objectives of this study are to estimate the extent of glacial retreat of the Fedchenko glacier from 1933 to 2014, and to estimate the mass balance of the Fedchenko in the Pamir region of Tajikistan. ASTER and Landsat satellite images were used in the study. Glacier terminus of the Fedchenko glacier retreated about 1.7 km over the last 81 years. However, in the recent years, the rate of retreat has slowed down. The lower part of the ablation zone, which is mostly debris covered has exhibited higher surface lowering trend compared to the area between the altitude of 3800m to the equilibrium line altitude (ELA).

Density assumptions for converting geodetic glacier volume change to mass change

Abstract. The geodetic method is widely used for assessing changes in the mass balance of mountain glaciers. However, comparison of repeated digital elevation models only provides a glacier volume change that must be converted to a change in mass using a density assumption or model. This study investigates the use of a constant factor for the volume-to-mass conversion based on a firn compaction model applied to simplified glacier geometries with idealized climate forcing, and two glaciers with long-term mass balance series. It is shown that the "density" of geodetic volume change is not a constant factor and is systematically smaller than ice density in most cases. This is explained by the accretion/removal of low-density firn layers, and changes in the firn density profile with positive/negative mass balance. Assuming a value of 850 ± 60 kg m−3 to convert volume change to mass change is appropriate for a wide range of conditions. For short time intervals (≤3 yr), periods with limited volume change, and/or changing mass balance gradients, the conversion factor can however vary from 0–2000 kg m−3 and beyond, which requires caution when interpreting glacier mass changes based on geodetic surveys.

The Younger Dryas climatic conditions in the Za Mnichem Valley (Polish High Tatra Mountains) based on exposure‐age dating and glacier‐climate modelling

Cosmogenic 36Cl was measured in bedrock and moraine boulders in the Za Mnichem Valley (High Tatra Mountains). The post‐LGM deglaciation of the study area occurred about 15.9 ka ago. The northernmost part of the valley slopes was ice‐free around 15 ka ago. The terminal moraine on the valley threshold was finally stabilized 12.5 ka ago during the Younger Dryas cold event (Greenland Stadial 1). At that time, the Za Mnichem glacier was 1.3 km long and had an area of 0.57 km2. The AAR equilibrium line of the glacier was located at 1990 m a.s.l., which corresponds to an ELA depression of ∼500 m compared to today. The mean summer temperature was colder by 4°–4.5°C than the present‐day temperature. The mean annual temperature was colder by 6°C than today. Such conditions suggest a decrease of the annual precipitation by ∼15–25% compared with the present‐day annual average. These data indicate a probable uniform temperature change across central and western Europe, with the precipitation being the most significant factor affecting the mass balance of mountain glaciers. The spatial distribution of balance data suggests increasing continentality towards the east during the Younger Dryas.

Observed Mass Balance of Mountain Glaciers and Greenland Ice Sheet in the 20th Century and the Present Trends

Glacier mass balance and secular changes in mountain glaciers and ice caps are evaluated from the annual net balance of 137 glaciers from 17 glacierized regions of the world. Further, the winter and summer balances for 35 glaciers in 11 glacierized regions are analyzed. The global means are calculated by weighting glacier and regional surface areas. The area-weighted global mean net balance for the period 1960–2000 is −270 ± 34 mm a−1 w.e. (water equivalent, in mm per year) or (−149 ± 19 km3 a−1 w.e.), with a winter balance of 890 ± 24 mm a−1 w.e. (490 ± 13 km3 a−1 w.e.) and a summer balance of −1,175 ± 24 mm a−1 w.e. (−647 ± 13 km3 a−1 w.e.). The linear-fitted global net balance is accelerating at a rate of −9 ± 2.1 mm a−2. The main driving force behind this change is the summer balance with an acceleration of −10 ± 2.0 mm a−2. The decadal balance, however, shows significant fluctuations: summer melt reached its peak around 1945, followed by a decrease. The negative trend in the annual net balance is interrupted by a period of stagnation from 1960s to 1980s. Some regions experienced a period of positive net balance during this time, for example, Europe. The balance has become strongly negative since the early 1990s. These decadal fluctuations correspond to periods of global dimming (for smaller melt) and global brightening (for larger melt). The total radiation at the surface changed as a result of an imbalance between steadily increasing greenhouse gases and fluctuating aerosol emissions. The mass balance of the Greenland ice sheet and the surrounding small glaciers, averaged for the period of 1950–2000, is negative at −74 ± 10 mm a−1 w.e. (−128 ± 18 km3 a−1 w.e.) with an accumulation of 297 ± 33 mm a−1 w.e. (519 ± 58 km3 a−1 w.e.), melt ablation −169 ± 18 mm a−1 w.e. (−296 ± 31 km3 a−1 w.e.), calving ablation −181 ± 19 mm a−1 w.e. (−316 ± 33 km3 a−1 w.e.) and the bottom melt-21 ± 2 mm a−1 w.e. (−35 ± 4 km3 a−1 w.e.). Almost half (−60 ± 3 km3 a−1) of the net mass loss comes from mountain glaciers and ice caps around the ice sheet. At present, it is difficult to detect any statistically significant trends for these components. The total mass balance of the Antarctic ice sheet is considered to be too premature to evaluate. The estimated sea-level contributions in the twentieth Century are 5.7 ± 0.5 cm by mountain glaciers and ice caps outside Antarctica, 1.9 ± 0.5 cm by the Greenland ice sheet, and 2 cm by ocean thermal expansion. The difference of 7 cm between these components and the estimated value with tide-gage networks (17 cm) must result from other sources such as the mass balance of glaciers of Antarctica, especially small glaciers separated from the ice sheet.

Global, regional and local scale factors determining glaciation extent in Eastern Siberia over the last 140,000 years

The aim of this work is to evaluate the effect of variations of greenhouse gas concentrations, orbital parameters, sea-surface conditions, vegetation and dust deposition on the extent of East Siberian mountain glaciations during the late Quaternary. An atmosphere-only general circulation model is used in a series of 16 sensitivity tests at high spatial resolution over the region of interest to systematically evaluate the relative importance of these different forcing parameters. No attempt was made to reproduce in detail the history of late Quaternary mountain glaciations in East Siberia, because, given (a) the temporal and spatial scarcity of available evidence of mountain glaciations in this region and (b) the large uncertainties concerning the boundary conditions to be prescribed in this model, such an exercise must necessarily remain incomplete and partially inconclusive. The results of this study suggest that moisture delivery from the Atlantic is an important factor determining mountain glacier mass balance in Eastern Siberia and is very sensitive to the geometry of the West Eurasian ice sheet. This means that variable moisture blocking by the West Eurasian ice sheet during the Weichselian is the most important single factor explaining the opposite history of glacier and ice sheet extent in West and East Eurasia during the Weichselian. This work confirms earlier results showing that the large 140 kyr BP West Eurasian ice sheet caused regional-scale cooling extending towards Eastern Eurasia. Nevertheless, the simulated response of the regional summer temperature (and thus glacier extent because of the strong dependency of glacier mass balance of summer melt rates) is to a very large extent directly determined by insolation. For the Early Weichselian, this leads to a clear maximum of local glacier extent at 70 kyr BP, which is in line with the variations of top-of-the-atmosphere insolation on orbital time scales, but to some degree at odds with geological evidence which suggests larger glacier extent at 115 and 90 kyr BP than at 70 kyr BP. Through snow feedbacks, the effects of changes in the prescribed vegetation distribution and dust deposition rate are also substantial. In summary, it appears that the broad features of late Quaternary glaciation history in Eastern Eurasia can be understood in terms of known forcings.

Chapter 9: Mass balance of mountain glaciers and the earth's climate

Chapter 9: Mass balance of mountain glaciers and the earth's climate