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Determining surface mass balance from DEM's

Written by Thomas Zwinger on .

Accum all annotThis article deals with the reconstruction of surface mass balance patterns based on digital elevation models (DEM's). Using two consecutive DEMs, Elmer/Ice has been used as a diagnostic model to evaluate the emergence velocity for a geometry defined as the arithmetic mean between these two DEMs. Using in addition a linearly between the DEMs interpolated local elevation change, one is able to reconstruct an average surface mass balance (SMB) for the period of interest. As the object of study, Midtre Lovénbreen (a small glacier in Svalbard, close to the Nye Ålesund station), has an accompanying excellent record of stake data measurements, the authors were able to compare the results from their new approach with in-situ observations. The advantages of the presented approach clearly are given by the facts that (provided the bedrock is known) surface DEMs can be obtained using modern remote sensing techniques and lead to a result for the inverted SMB covering the whole glacier, whereas in-situ measurements usually are confined to a limited area of the glacier.

Read more:  Välisuo, I., T. Zwinger and J. Kohler, 2017. Inverse solution of surface mass balance of Midtre Lovénbreen, Svalbard, Journal of Glaciology, 1-10, doi:10.1017/jog.2017.26.

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ITMIX: How accurate are estimates of glacier ice thickness?

Written by Olivier Gagliardini on .

itmixElmer/Ice used to build 3 synthetic cases for the ITMIX intercomparisoon exercice, but also as a participating models. 

Abstract: Knowledge of the ice thickness distribution of glaciers and ice caps is an important prerequisite for many glaciological and hydrological investigations. A wealth of approaches has recently been presented for inferring ice thickness from characteristics of the surface. With the Ice Thickness Models Intercomparison eXperiment (ITMIX) we performed the first coordinated assessment quantifying individual model performance. A set of 17 different models showed that individual ice thickness estimates can differ considerably – locally by a spread comparable to the observed thickness. Averaging the results of multiple models, however, significantly improved the results: on average over the 21 considered test cases, comparison against direct ice thickness measurements revealed deviations on the order of 10 ± 24 % of the mean ice thickness (1σ estimate). Models relying on multiple data sets – such as surface ice velocity fields, surface mass balance, or rates of ice thickness change – showed high sensitivity to input data quality. Together with the requirement of being able to handle large regions in an automated fashion, the capacity of better accounting for uncertainties in the input data will be a key for an improved next generation of ice thickness estimation approaches.

Read more:  Farinotti, D. and others, 2017. How accurate are estimates of glacier ice thickness? Results from ITMIX, the Ice Thickness Models Intercomparison eXperiment, The Cryosphere, 11, 949-970, doi:10.5194/tc-11-949-2017.

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Modeling the Controls on the Front Position of a Tidewater Glacier in Svalbard

Written by Olivier Gagliardini on .

Calving is an important masOtero Fig8s-loss process at ice sheet and marine-terminating glacier margins, but identifying and quantifying its principal driving mechanisms remains challenging. Hansbreen is a grounded tidewater glacier in southern Spitsbergen, Svalbard, with a rich history of field and remote sensing observations. The available data make this glacier suitable for evaluating mechanisms and controls on calving, some of which are considered in this paper. We use a full-Stokes thermomechanical 2D flow model (Elmer/Ice), paired with a crevasse-depth calving criterion, to estimate Hansbreen’s front position at a weekly time resolution. The basal sliding coefficient is re-calibrated every 4 weeks by solving an inverse model. We investigate the possible role of backpressure at the front (a function of ice mélange concentration) and the depth of water filling crevasses by examining the model’s ability to reproduce the observed seasonal cycles of terminus advance and retreat. Our results suggest that the ice-mélange pressure plays an important role in the seasonal advance and retreat of the ice front, and that the crevasse-depth calving criterion, when driven by modeled surface meltwater, closely replicates observed variations in terminus position. These results suggest that tidewater glacier behavior is influenced by both oceanic and atmospheric processes, and that neither of them should be ignored.

More information: Otero J, F.J. Navarro, J.J. Lapazaran, E. Welty, D. Puczko and R. Finkelnburg, 2017. Modeling the Controls on the Front Position of a Tidewater Glacier in Svalbard. Front. Earth Sci. 5:29. doi:10.3389/feart.2017.00029.

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