Glacier Surface Mass Balance Research Articles

Snowdrift modelling for the Vestfonna ice cap, north-eastern Svalbard

Abstract. The redistribution of snow by drifting and blowing snow frequently leads to an inhomogeneous snow mass distribution on larger ice caps. Together with the thermodynamic impact of drifting snow sublimation on the lower atmospheric boundary layer, these processes affect the glacier surface mass balance. This study provides a first quantification of snowdrift and sublimation of blowing and drifting snow on the Vestfonna ice cap (Svalbard) by using the specifically designed snow2blow snowdrift model. The model is forced by atmospheric fields from the Polar Weather Research and Forecasting model and resolves processes on a spatial resolution of 250 m. The model is applied to the Vestfonna ice cap for the accumulation period 2008/2009. Comparison with radio-echo soundings and snow-pit measurements show that important local-scale processes are resolved by the model and the overall snow accumulation pattern is reproduced. The findings indicate that there is a significant redistribution of snow mass from the interior of the ice cap to the surrounding areas and ice slopes. Drifting snow sublimation of suspended snow is found to be stronger during spring. It is concluded that the redistribution process is strong enough to have a significant impact on glacier mass balance.

Irreversible mass loss of Canadian Arctic Archipelago glaciers

AbstractThe Canadian Arctic Archipelago (CAA) contains the largest volume of glacier ice on Earth outside of Antarctica and Greenland. In the absence of significant calving, CAA glacier mass balance is governed by the difference between surface snow accumulation and meltwater runoff—surface mass balance. Here we use a coupled atmosphere/snow model to simulate present‐day and 21st century CAA glacier surface mass balance. Through comparison with Gravity Recovery and Climate Experiment mass anomalies and in situ observations, we show that the model is capable of representing present‐day CAA glacier mass loss, as well as the dynamics of the seasonal snow cover on the CAA tundra. Next, we force this model until 2100 with a moderate climate warming scenario (AR5 RCP4.5). We show that enhanced meltwater runoff from CAA glaciers is not sufficiently compensated by increased snowfall. Extrapolation of these results toward an AR5 multimodel ensemble results in sustained 21st century CAA glacier mass loss in the vast majority (>99%) of the ~7000 temperature realizations.

Energy and mass balance of Zhadang glacier surface, central Tibetan Plateau

AbstractClimate variables that control the annual cycle of the surface energy and mass balance on Zhadang glacier in the central Tibetan Plateau were examined over a 2 year period using a physically based energy-balance model forced by routine meteorological data. The modelled results agree with measured values of albedo, incoming longwave radiation, surface temperature and surface level of the glacier. For the whole observation period, the radiation component dominated (82%) the total surface energy heat fluxes. This was followed by turbulent sensible (10%) and latent heat (6%) fluxes. Subsurface heat flux represented a very minor proportion (2%) of the total heat flux. The sensitivity of specific mass balance was examined by perturbations of temperature (±1 K), relative humidity (±20%) and precipitation (±20%). The results indicate that the specific mass balance is more sensitive to changes in precipitation than to other variables. The main seasonal variations in the energy balance were in the two radiation components (net shortwave radiation and net longwave radiation) and these controlled whether surface melting occurred. A dramatic difference in summer mass balance between 2010 and 2011 indicates that the glacier surface mass balance was closely related to precipitation seasonality and form (proportion of snowfall and rainfall).

A physically based model of the year-round surface energy and mass balance of debris-covered glaciers

AbstractDebris-covered glaciers respond to atmospheric conditions in different ways from debris-free glaciers, due to the presence of debris at the surface during the ablation season and at the snow/ice interface during the accumulation season. Understanding the response of debris-covered glaciers to a variety of meteorological conditions in a physically sound manner is essential to quantify meltwater discharge and to predict their response to climate change. To tackle this issue, we developed the Crocus-DEB model as an adaptation of the detailed snowpack model Crocus, to simulate the energy and mass balance of debris-covered glaciers, including periods when debris is covered by snow. Crocus-DEB was evaluated with data gathered during a field experiment using artificial debris covering the snowpack at Col de Porte, France, with very good results in terms of conductive heat flux, both at the surface and at the interface between the debris and the underlying dense snow taken as a surrogate for ice, with and without snow overlying the debris. The model was also evaluated using field data from the debris-covered glacier Changri Nup, Nepal, Himalaya. This paper introduces the design of the model, its performance and its ability to explore relationships between model parameters, meteorological conditions and the critical debris thickness.

Past and future sea-level change from the surface mass balance of glaciers

Abstract. We present estimates of sea-level change caused by the global surface mass balance of glaciers, based on the reconstruction and projection of the surface mass balance of all the individual glaciers of the world, excluding the ice sheets in Greenland and Antarctica. The model is validated using a leave-one-glacier-out cross-validation scheme against 3997 observed surface mass balances of 255 glaciers, and against 756 geodetically observed, temporally integrated volume and surface area changes of 341 glaciers. When forced with observed monthly precipitation and temperature data, the glaciers of the world are reconstructed to have lost mass corresponding to 114 ± 5 mm sea-level equivalent (SLE) between 1902 and 2009. Using projected temperature and precipitation anomalies from 15 coupled general circulation models from the Coupled Model Intercomparison Project phase 5 (CMIP5) ensemble, they are projected to lose an additional 148 ± 35 mm SLE (scenario RCP26), 166 ± 42 mm SLE (scenario RCP45), 175 ± 40 mm SLE (scenario RCP60), or 217 ± 47 mm SLE (scenario RCP85) during the 21st century. Based on the extended RCP scenarios, glaciers are projected to approach a new equilibrium towards the end of the 23rd century, after having lost either 248 ± 66 mm SLE (scenario RCP26), 313 ± 50 mm SLE (scenario RCP45), or 424 ± 46 mm SLE (scenario RCP85). Up until approximately 2100, ensemble uncertainty within each scenario is the biggest source of uncertainty for the future glacier mass loss; after that, the difference between the scenarios takes over as the biggest source of uncertainty. Ice mass loss rates are projected to peak 2040 ∼ 2050 (RCP26), 2050 ∼ 2060 (RCP45), 2070 ∼ 2090 (RCP60), or 2070 ∼ 2100 (RCP85).

Properties of natural supraglacial debris in relation to modelling sub‐debris ice ablation

ABSTRACTAs debris‐covered glaciers become a more prominent feature of a shrinking mountain cryosphere, there is increasing need to successfully model the surface energy and mass balance of debris‐covered glaciers, yet measurements of the processes operating in natural supraglacial debris covers are sparse. We report measurements of vertical temperature profiles in debris on the Ngozumpa glacier in Nepal, that show: (i) conductive processes dominate during the ablation season in matrix‐supported diamict; (ii) ventilation may be possible in coarse surface layers; (iii) phase changes associated with seasonal change have a marked effect on the effective thermal diffusivity of the debris. Effective thermal conductivity determined from vertical temperature profiles in the debris is generally ~30% higher in summer than in winter, but values depend on the volume and phase of water in the debris. Surface albedo can vary widely over small spatial scales, as does the debris thickness. Measurements indicate that debris thickness is best represented as a probability density function with the peak debris thickness increasing down‐glacier. The findings from Ngozumpa glacier indicate that the probability distribution of debris thickness changes from positively skewed in the upper glacier towards a more normal distribution nearer the terminus. Although many of these effects remain to be quantified, our observations highlight aspects of spatial and temporal variability in supraglacial debris that may require consideration in annual or multi‐annual distributed modelling of debris‐covered glacier surface energy and mass balance. Copyright © 2012 John Wiley & Sons, Ltd.

A minimal model for reconstructing interannual mass balance variability of glaciers in the European Alps

Abstract. We present a minimal model of the glacier surface mass balance. The model relies solely on monthly precipitation and air temperatures as forcing. We first train the model individually for 15 glaciers with existing mass balance measurements. Based on a cross validation, we present a thorough assessment of the model's performance outside of the training period. The cross validation indicates that our model is robust, and our model's performance compares favorably to that from a less parsimonious model based on seasonal sensitivity characteristics. Then, the model is extended for application on glaciers without existing mass balance measurements. We cross validated the model again by withholding the mass balance information from each of the 15 glaciers above during the model training, in order to measure its performance on glaciers not included in the model training. This cross validation indicates that the model retains considerable skill even when applied on glaciers without mass balance measurements. As an exemplary application, the model is then used to reconstruct time series of interannual mass balance variability, covering the past two hundred years, for all glaciers in the European Alps contained in the extended format of the world glacier inventory. Based on this reconstruction, we present a spatially detailed attribution of the glaciers' mass balance variability to temperature and precipitation variability.

Ice flux divergence anomalies on 79north Glacier, Greenland

The ice flux divergence of a glacier is an important quantity to examine because it determines the rate of temporal change of its thickness. Here, we combine high‐resolution ice surface velocity observations of Nioghalvfjerdsfjorden (79north) Glacier, a major outlet glacier in north Greenland, with a dense grid of ice thickness data collected with an airborne radar sounder in 1998, to examine its ice flux divergence. We detect large variations, up to 100 m/yr, in flux divergence on grounded ice that are incompatible with what we know of the glacier surface mass balance, basal mass balance and thinning rate. We examine the hypothesis that these anomalies are due to the three‐dimensional flow of ice around and atop bumps and hollows in basal topography by comparing the flux divergence of three‐dimensional numerical models with its surface equivalent. We find that three‐dimensional effects have only a small contribution to the observed anomalies. On the other hand, if we degrade the spatial resolution of the data to 10 km the anomalies disappear. Further analysis shows that the source of the anomalies is not the ice velocity data but the interpolation of multiple tracks of ice thickness data onto a regular grid using a scheme (here block kriging) that does not conserve mass or ice flux. This problem is not unique to 79north Glacier but is common to all conventional ice thickness surveys of glaciers and ice sheets; and fundamentally limits the application of ice thickness grids to high‐resolution numerical modeling of glacier flow.

Surface mass balance and ice flow of the glaciers Austre Lovénbreen and Pedersenbreen, Svalbard, Arctic

The glaciersAustre Lovenbreen and Pedersenbreen are located at Nylesund, Svalbard. The surface mass balance and ice flow velocity of both glaciers have been determined from the first year of observations (2005/2006), while the front edge of Austre Lovenbreen was also surveyed. The results are as follows：(1) The net mass balances of Austre Lovenbreen and Pedersenbreen are -0.44 and -0.20 m w.e., the annual ablation is -0.99 and -0.94 m w.e., and the corresponding equilibrium line altitudes are 478.10 and 494.87 m, respectively. (2) Austre Lovenbreen and Pedersenbreen are characterized as ice flow models of surge type glaciers in Svalbard. The horizontal vectors of the ice flow velocities are parallel or converge to the central lines of both glaciers, with lower velocities in the lower ablation areas and higher velocities in the middle and upper reaches of the glaciers. The vertical vectors of ice flow velocities show that there is a mass loss in the ablation areas, which reduces with increasing altitude, while there is a mass gain near the equilibrium line of Austre Lovenbreen. (3) The front edge of Austre Lovenbreen receded at an average rate of 21.83 m?a -1 , with remarkable variability a maximum rate of 77.30 m?a -1 and a minimum rate of 2.76 m?a -1 .

Modeling the surface mass balance of a high Arctic glacier using the ERA‐40 reanalysis

Investigating glacier mass balance via the use of numerical models provides an important insight into glacier‐climate interactions and allows for the assessment of future changes in sea level and local water resources. The application of mass balance models to unmonitored regions has previously been inhibited by the inadequate spatial coverage of local meteorological observations. One way to overcome this problem is through the use of climate reanalysis products. In this paper we evaluate the ability of the European Centre for Medium‐Range Forecasts ERA‐40 reanalysis to drive a surface mass balance model of Midre Lovénbreen, northwest Spitsbergen, Svalbard. The ERA‐40 reanalysis is validated and bias‐corrected against long‐term observations from two nearby in situ weather stations. The model is calibrated over the period of mass balance observations (1968–2001) using a downhill simplex parameter optimization technique to minimize the error between observed and simulated mass balances. The calibrated model is then used to extend the mass balance record of Midre Lovénbreen back to the beginning of the reanalysis in 1958. Overall, the ERA‐40 reanalysis is found to correspond sufficiently well with surface observations to be used for mass balance modeling. When driven using the ERA‐40 reanalysis, the calibrated surface mass balance model performs very well. The area‐averaged cumulative errors for winter, summer, and net balances are all very small over the period 1968–2001 (<0.3 m water equivalent (w.e.)). For the centerline stakes the correlation coefficients between observed and modeled net, winter, and summer balances are 0.83, 0.84, and 0.77, respectively. Using the hindcasted mass balances, a mean cumulative mass loss of −17.8 ± 3.7 m w.e. is estimated over the 44 year period 1958–2001.

100‐year mass changes in the Swiss Alps linked to the Atlantic Multidecadal Oscillation

Thirty new 100‐year records of glacier surface mass balance, accumulation and melt in the Swiss Alps are presented. The time series are based on a comprehensive set of field data and distributed modeling and provide insights into the glacier‐climate linkage. Considerable mass loss over the 20th century is evident for all glaciers, but rates differ strongly. Glacier mass loss shows multidecadal variations and was particularly rapid in the 1940s and since the 1980s. Mass balance is significantly anticorrelated to the Atlantic Multidecadal Oscillation (AMO) index assumed to be linked to thermohaline ocean circulation. We show that North Atlantic variability had a recognizable impact on glacier changes in the Swiss Alps for at least 250 years.

THE STUDIES OF SURFACE MASS BALANCE AND ICE FLOW ON GLACIERS AUSTRELOVéNBREEN AND PEDERSENBREEN,SVALBARD,ARCTIC

The glaciers Austre Lovenbreen and Pedersenbreen are located at Ny-lesund, Svalbard. Based on the observation of first year (2005/2006), surface mass balance and ice flow velocity of both glaciers have been analysed, while the front edge of Austre Lovenbreen has also been surveyed. The results are as following: (1) The net mass balance of Austre Lovenbreen and Pedersenbreen is -0.44 and -0.20 m w.e., respectively. Their annual ablation is -0.99 and -0.94 m w.e., respectively, and corresponding ELA is 478.10 and 494.87m, respectively. (2) Austre Lovenbreen and Pedersenbreen are characterized as ice flow model of surge-type glaciers in Svalbard. The level vectors of ice flow velocity are parallel or converge to the central lines of both glaciers, with slower velocities at the lower ablation area and relatively faster ones at the middle and upper part of glaciers. The mean, maximum and minimum of ice flow velocities on Austre Lovenbreen are 2.28, 3.91 and 0.81 m·a-1, and Pedersenbreen's are 6.74, 8.13 and 5.49 m·a-1. The vertical vectors of ice flow velocity show that there is a mass loss in the ablation area, which weakness with the increase of altitude, while there exists a mass gain near ELA on Austre Lovenbreen. The actual vertical displacement is in accord with the general pattern that motion is downward in the accumulation area, and is, by contrast, upward in the ablation area. (3) The front edge of Austre Lovenbreen has receded at an average rate of 21.83 m.a-1, with maximum 77.30 m.a-1 and minimum 2.76 m.a-1.

TEMPERATURE VARIATIONS AT THE GREAT WALL STATION (1985—2008) AND ZHONGSHAN STATION (1989—2008),ANTARCTIC

The glaciers Austre Lovenbreen and Pedersenbreen are located at Ny-lesund, Svalbard. Based on the observation of first year (2005/2006), surface mass balance and ice flow velocity of both glaciers have been analysed, while the front edge of Austre Lovenbreen has also been surveyed. The results are as following: (1) The net mass balance of Austre Lovenbreen and Pedersenbreen is -0.44 and -0.20 m w.e., respectively. Their annual ablation is -0.99 and -0.94 m w.e., respectively, and corresponding ELA is 478.10 and 494.87m, respectively. (2) Austre Lovenbreen and Pedersenbreen are characterized as ice flow model of surge-type glaciers in Svalbard. The level vectors of ice flow velocity are parallel or converge to the central lines of both glaciers, with slower velocities at the lower ablation area and relatively faster ones at the middle and upper part of glaciers. The mean, maximum and minimum of ice flow velocities on Austre Lovenbreen are 2.28, 3.91 and 0.81 m·a-1, and Pedersenbreen's are 6.74, 8.13 and 5.49 m·a-1. The vertical vectors of ice flow velocity show that there is a mass loss in the ablation area, which weakness with the increase of altitude, while there exists a mass gain near ELA on Austre Lovenbreen. The actual vertical displacement is in accord with the general pattern that motion is downward in the accumulation area, and is, by contrast, upward in the ablation area. (3) The front edge of Austre Lovenbreen has receded at an average rate of 21.83 m.a-1, with maximum 77.30 m.a-1 and minimum 2.76 m.a-1.

Mountain glaciers and ice caps around Antarctica make a large sea‐level rise contribution

The Intergovernmental Panel on Climate Change (IPCC) estimates that the sum of all contributions to sea‐level rise for the period 1961–2004 was 1.1 ± 0.5 mm a−1, leaving 0.7 ± 0.7 of the 1.8 ± 0.5 mm a−1 observed sea‐level rise unexplained. Here, we compute the global surface mass balance of all mountain glaciers and ice caps (MG&IC), and find that part of this much‐discussed gap can be attributed to a larger contribution than previously assumed from mass loss of MG&IC, especially those around the Antarctic Peninsula. We estimate global surface mass loss of all MG&IC as 0.79 ± 0.34 mm a−1 sea‐level equivalent (SLE) compared to IPCC's 0.50 ± 0.18 mm a−1. The Antarctic MG&IC contributed 28% of the global estimate due to exceptional warming around the Antarctic Peninsula and high sensitivities to temperature similar to those we find in Iceland, Patagonia and Alaska.

Measured and modelled sublimation on the tropical Glaciar Artesonraju, Perú

Abstract. Sublimation plays a decisive role in the surface energy and mass balance of tropical glaciers. During the dry season (May–September) low specific humidity and high surface roughness favour the direct transition from ice to vapour and drastically reduce the energy available for melting. However, field measurements are scarce and little is known about the performance of sublimation parameterisations in glacier mass balance and runoff models. During 15 days in August 2005 sublimation was measured on the tongue of Glaciar Artesonraju (8°58' S, 77°38' W) in the Cordillera Blanca, Perú, using simple lysimeters. Indicating a strong dependence on surface roughness, daily totals of sublimation range from 1–3 kg m−2 for smooth to 2–5 kg m−2 for rough conditions. (The 15-day means at that time of wind speed and specific humidity were 4.3 m s−1 and 3.8 g kg−1, respectively.) Measured sublimation was related to characteristic surface roughness lengths for momentum (zm) and for the scalar quantities of temperature and water vapour (zs), using a process-based mass balance model. Input data were provided by automatic weather stations, situated on the glacier tongue at 4750 m a.s.l. and 4810 m a.s.l., respectively. Under smooth conditions the combination zm=2.0 mm and zs=1.0 mm appeared to be most appropriate, for rough conditions zm=20.0 mm and zs=10.0 mm fitted best. Extending the sublimation record from April 2004 to December 2005 with the process-based model confirms, that sublimation shows a clear seasonality. 60–90% of the energy available for ablation is consumed by sublimation in the dry season, but only 10–15% in the wet season (October–April). The findings are finally used to evaluate the parameterisation of sublimation in the lower-complexity mass balance model ITGG, which has the advantage of requiring precipitation and air temperature as only input data. It turns out that the implementation of mean wind speed is a possible improvement for the representation of sublimation in the ITGG model.

A method to estimate the ice volume and ice-thickness distribution of alpine glaciers

AbstractSound knowledge of the ice volume and ice-thickness distribution of a glacier is essential for many glaciological applications. However, direct measurements of ice thickness are laborious, not feasible everywhere and necessarily restricted to a small number of glaciers. In this paper, we present a method to estimate the ice-thickness distribution and the total ice volume of alpine glaciers. This method is based on glacier mass turnover and principles of ice-flow mechanics. The required input data are the glacier surface topography, the glacier outline and a set of borders delineating different ‘ice-flow catchments’. Three parameters describe the distribution of the ‘apparent mass balance’, which is defined as the difference between the glacier surface mass balance and the rate of ice-thickness change, and two parameters define the ice-flow dynamics. The method was developed and validated on four alpine glaciers located in Switzerland, for which the bedrock topography is partially known from radio-echo soundings. The ice thickness along 82 cross-profiles can be reproduced with an average deviation of about 25% between the calculated and the measured ice thickness. The cross-sectional areas differ by less than 20% on average. This shows the potential of the method for estimating the ice-thickness distribution of alpine glaciers without the use of direct measurements.

Modelling runoff from highly glacierized alpine drainage basins in a changing climate

AbstractThe future runoff from three highly glacierized alpine catchments is assessed for the period 2007–2100 using a glacio‐hydrological model including the change in glacier coverage. We apply scenarios for the seasonal change in temperature and precipitation derived from regional climate models. Glacier surface mass balance and runoff are calculated in daily time‐steps using a distributed temperature‐index melt and accumulation model. Model components account for changes in glacier extent and surface elevation, evaporation and runoff routing. The model is calibrated and validated using decadal ice volume changes derived from four digital elevation models (DEMs) between 1962 and 2006, and monthly runoff measured at a gauging station (1979–2006). Annual runoff from the drainage basins shows an initial increase which is due to the release of water from glacial storage. After some decades, depending on catchment characteristics and the applied climate change scenario, runoff stabilizes and then drops below the current level. In all climate projections, the glacier area shrinks dramatically. There is an increase in runoff during spring and early summer, whereas the runoff in July and August decreases significantly. This study highlights the impact of glaciers and their future changes on runoff from high alpine drainage basins. Copyright © 2008 John Wiley & Sons, Ltd.

Assessment of interannual variations in the surface mass balance of 18 Svalbard glaciers from the Moderate Resolution Imaging Spectroradiometer/Terra albedo product

We estimate annual anomalies of the surface mass balance of glaciers on Svalbard for the period 2000–2005 (six years), by calculating the so‐called “satellite‐derived mass balance” (Bsat) from time series of satellite‐derived surface albedos. The method needs no other input variables. Surface albedos are extracted from the Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra albedo product. We validate the MODIS albedos by comparing them with in situ measurements on Kongsvegen, and we find a low root‐mean‐square error of 0.04 for higher‐quality MODIS data. Confidence in the MODIS product is also provided by realistic profiles of albedo along glacier centerlines. We apply the method to 18 glaciers that are evenly distributed over the archipelago. Correlation coefficients of time series of Bsat and direct measurements of the annual mass balance on Kongsvegen and Hansbreen are highly significant (0.94 and 0.82, respectively). Moreover, spatial distributions of the anomalies for individual years are coherent. Disadvantages of the method are that absolute values of the mass balance cannot be determined and that the interannual variability is underestimated. The latter might be corrected by equations to be established with mass balance models.

Surface mass balance of glaciers in the French Alps: distributed modeling and sensitivity to climate change

AbstractA new physically based distributed surface mass-balance model is presented for Alpine glaciers. Based on the Crocus prognostic snow model, it resolves both the temporal (1 hour time-step) and spatial (200 m grid-step) variability of the energy and mass balance of glaciers. Mass-balance reconstructions for the period 1981–2004 are produced using meteorological reconstruction from the SAFRAN meteorological model for Glacier de Saint-Sorlin and Glacier d’Argentière, French Alps. Both glaciers lost mass at an accelerated rate in the last 23 years. The spatial distribution of precipitation within the model grid is adjusted using field mass-balance measurements. This is the only correction made to the SAFRAN meteorological input to the glacier model, which also includes surface atmospheric temperature, moisture, wind and all components of downward radiation. Independent data from satellite imagery and geodetic measurements are used for model validation. With this model, glacier sensitivity to climate change can be separately evaluated with respect to a full range of meteorological parameters, whereas simpler models, such as degree-day models, only account for temperature and precipitation. We provide results for both mass balance and equilibrium-line altitude (ELA) using a generic Alpine glacier. The sensitivity of the ELA to air temperature alone is found to be 125 m °C–1, or 160 m °C¯1 if concurrent (Stefan–Boltzmann) longwave radiation change is taken into account.