Application of a two-step approach for mapping ice thickness  to various glacier types on Svalbard

Fürst, Johannes J.; Gillet-Chaulet, Fabien; Benham, Toby; Dowdeswell, Julian A.; Grabiec, Mariusz; Navarro, Francisco; Pettersson, R.; Moholdt, Geir; Nuth, C.; Saß, Björn; Schanke, Kjetil; Fettweis, Xavier; Lang, Charlotte; Seehaus, Thorsten; Braun, Matthias

doi:10.5194/tc-11-2003-2017

Cited by 43 publications

(61 citation statements)

References 92 publications

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“…The volume of glaciers with calibration differed by 2%, with a mean absolute difference of 10% to modeled volume presented in this study. Computationally more expensive approaches (e.g., Morlighem et al, 2011;Fürst et al, 2017) are well capable of assimilating direct measurements. As our goal is to apply a calibrated model to all glaciers in Austria, most of which are not covered by direct observations, we preferred to stay with the simple forward method.…”

Section: Discussionmentioning

confidence: 99%

Calibrated Ice Thickness Estimate for All Glaciers in Austria

2019

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Knowledge on ice thickness distribution and total ice volume is a prerequisite for computing future glacier change for both glaciological and hydrological applications. Various ice thickness estimation methods have been developed but regional differences in fundamental model parameters are substantial. Parameters calibrated with measured data at specific points in time and space can vary when glacier geometry and dynamics change. This study contributes to a better understanding of accuracies and limitations of modeled ice thicknesses by taking advantage of a comprehensive data set of in-situ ice thickness measurements from 58 glaciers in the Austrian Alps and observed glacier geometries of three Austrian glacier inventories (GI) between 1969 and 2006. The field data are used to calibrate an established ice thickness model to calculate an improved ice thickness data set for the Austrian Alps. A cross-validation between modeled and measured point ice thickness indicates a model uncertainty of 25-31% of the measured point ice thickness. The comparison of the modeled and measured average glacier ice thickness revealed an underestimation of 5% with a mean standard deviation of 15% for the glaciers with calibration data. The apparent mass balance gradient, the primary model parameter accounting for the effects of surface mass balance distribution as well as ice flux, substantially decreases over time and has to be adjusted for each temporal increment to correctly reproduce observed ice thickness. This reflects the general stagnation of glaciers in Austria. Using the calibrated parameter set, 93% of the observed ice thickness change on a glacier-specific scale could be captured for the periods between the GI. We applied optimized apparent mass balance gradients to all glaciers of the latest Austrian glacier inventory and found a volume of 15.9 km 3 for the year 2006. The ten largest glaciers account for 25% of area and 35% of total ice volume. An estimate based on mass balance measurements from nine glaciers indicates an additional volume loss of 3.5 ± 0.4 km 3 (i.e., 22 ± 2.5%) until 2016. Relative changes in area and volume were largest at glaciers smaller than 1 km 2 , and relative volume changes appear to be higher than relative area changes for all considered time periods.

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Section: Discussionmentioning

confidence: 99%

Calibrated Ice Thickness Estimate for All Glaciers in Austria

2019

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“…Ordered by the glacier area for which a solution was provided ( Fig. 1), the models included those by Huss and Farinotti 30 (Model 1), Frey et al 29 (Model 2), Maussion et al 33 (Model 3), Fürst et al 32 (Model 4) and Ramsankaran et al 34 (Model 5). These models are capable of inverting for glacier ice thickness distributions at the mountain range scale.…”

Section: Methodsmentioning

confidence: 99%

“…Here we take advantage of the ITMIX findings and use a combination of up to five ice thickness estimation models 29,30,[32][33][34] ( Fig. 1) to provide an ensemble-based estimate for the ice thickness distribution of each of the about 215,000 glaciers included in the Randolph Glacier Inventory (RGI) version 6.0 (ref.…”

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confidence: 99%

A consensus estimate for the ice thickness distribution of all glaciers on Earth

et al. 2019

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G laciers and ice caps outside the Greenland and Antarctic ice sheets ('glaciers' in the following) are changing rapidly in response to climate change 1 . Although they only contain a fraction of the worldwide ice volume 2 , the consequences of their mass loss are widespread and of global significance: glacier changes affect global trends in freshwater availability 3,4 , have dominated cryospheric contributions to recent sea level changes 5,6 and are anticipated to affect regional water resources over the twenty-first century 7,8 . Clearly, projections of such impacts require an estimate of the ice volume stored within present-day glaciers, and for regionalto local-scale projections the ice thickness distribution can also be essential 9,10 . Recent studies showed that even small features in the bedrock topography can cause decadal-scale variations in both ice dynamics response 11 and subglacial water discharge 12 .Despite far-reaching implications, knowledge of the ice thickness distributions of the world's glaciers is remarkably limited. The Glacier Thickness Database (GlaThiDa), which centralizes ice thickness measurements outside the two ice sheets, presently contains information for only about 1,000 out of the 215,000 glaciers worldwide 13 . This is despite important advances in the instrumentation used to measure ice thickness 14,15 , with airborne platforms now capable of operating in mountainous environments as well 16 .Owing to the lack of direct measurements, relations between glacier area and ice volume 17 have traditionally been used to estimate global glacier volumes 18-21 . For individual glaciers, instead, a suite of methods that infer the spatial ice thickness distribution from surface characteristics have been proposed [22][23][24][25][26][27] . Such methods use topographical information-typically extracted from digital elevation models (DEMs)-to estimate the distribution of the glacier's surface mass balance and, hence, its mass turnover. Knowledge of the ice thickness distribution of the world's glaciers is a fundamental prerequisite for a range of studies.Projections of future glacier change, estimates of the available freshwater resources or assessments of potential sea-level rise all need glacier ice thickness to be accurately constrained. Previous estimates of global glacier volumes are mostly based on scaling relations between glacier area and volume, and only one study provides global-scale information on the ice thickness distribution of individual glaciers. Here we use an ensemble of up to five models to provide a consensus estimate for the ice thickness distribution of all the about 215,000 glaciers outside the Greenland and Antarctic ice sheets. The models use principles of ice flow dynamics to invert for ice thickness from surface characteristics. We find a total volume of 158 ± 41 × 10 3 km 3 , which is equivalent to 0.32 ± 0.08 m of sea-level change when the fraction of ice located below present-day sea level (roughly 15%) is subtracted. Our results indicate that High Mountain Asia ...

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“…Beside volume-area scaling (e.g., [5,6]), techniques have been developed that make use of surface velocity information (e.g., [7]), parameterisations of the basal shear stress (e.g., [8][9][10][11]) or mass conservation (e.g., [12][13][14]). Other approaches cast the thickness reconstruction as a minimisation problem (e.g., [15][16][17]). Results from the Ice Thickness Models Intercomparison eXperiment (ITMIX, [18]) revealed that pooling the results from several models can significantly reduce the associated uncertainty as compared to individual results.…”

Section: Introductionmentioning

confidence: 99%

“…The transfer of mass from the upper plateau to the lower glacier trunk by ice avalanches is sporadic and not predictable by us in time. Many approaches participating in ITMIX use the difference between their simulated SMB and the contemporaneous surface elevation changes, also referred as the apparent mass balance [12,17]. However, climate parameters like the SMB abruptly change at the cliff by the large height difference.…”

Section: Introductionmentioning

confidence: 99%

Uncertainty Assessment of Ice Discharge Using GPR-Derived Ice Thickness from Gourdon Glacier, Antarctic Peninsula

et al. 2019

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Ice cliffs within a glacier represent a challenge for the continuity equations used in many glacier models by interrupting the validity of input parameters. In the case of Gourdon Glacier on James Ross Island, Antarctica, a ∼300–500 m high, almost vertical cliff, separates the outlet glacier from its main accumulation area on the plateau of the island. In 2017 and 2018 we conducted ice thickness measurements during two airborne ground penetrating radar campaigns in order to evaluate differences to older measurements from the 1990s. The observed differences are mostly smaller than the estimated error bars. In comparison to the in situ data, the published “consensus ice thickness estimate” strongly overestimates the ice thickness at the outlet. We analyse three different interpolation and ice thickness reconstruction methods. One approach additionally includes the mass input from the plateau. Differences between the interpolation methods have a minor impact on the ice discharge estimation if the used flux gates are in areas with a good coverage of in situ measurements. A much stronger influence was observed by uncertainties in the glacier velocities derived from remote sensing, especially in the direction of the velocity vector in proximity to the ice cliff. We conclude that the amount of in situ measurements should be increased for specific glacier types in order to detect biases in modeled ice thickness and ice discharge estimations.

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Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard

Cited by 43 publications

References 92 publications

Calibrated Ice Thickness Estimate for All Glaciers in Austria

Calibrated Ice Thickness Estimate for All Glaciers in Austria

A consensus estimate for the ice thickness distribution of all glaciers on Earth

Uncertainty Assessment of Ice Discharge Using GPR-Derived Ice Thickness from Gourdon Glacier, Antarctic Peninsula

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