Mass Balance Re-analysis of Findelengletscher, Switzerland; Benefits of Extensive Snow Accumulation Measurements

Abstract

A re-analysis is presented here of a 10 year mass balance series at Findelengletscher, a temperate mountain glacier in Switzerland. Calculating glacier-wide mass balance from the set of glaciological point balance observations using conventional approaches, such as the profile or contour method, resulted in significant deviations from the reference value given by the geodetic mass change over a 5 year period. This is attributed to the sparsity of observations at high elevations and to the inability of the evaluation schemes to adequately estimate accumulation in unmeasured areas. However, measurements of winter mass balance were available for large parts of the study period from snow probings and density pits. Complementary surveys by helicopter-borne ground-penetrating radar (GPR) were conducted in three consecutive years. The complete set of seasonal observations was assimilated using a distributed mass balance model. This model-based extrapolation revealed a substantial mass loss at Findelengletscher of −0.43 m w.e. a −1 between 2004 and 2014, while the loss was less pronounced for its former tributary, Adlergletscher (−0.30 m w.e. a −1 ). For both glaciers, the resulting time series were within the uncertainty bounds of the geodetic mass change. We show that the model benefited strongly from the ability to integrate seasonal observations. If no winter mass balance measurements were available and snow cover was represented by a linear precipitation gradient, the geodetic mass balance was not matched. If winter balance measurements by snow probings and snow density pits were taken into account, the model performance was substantially improved but still showed a significant bias relative to the geodetic mass change. Thus, the excellent agreement of the model-based extrapolation with the geodetic mass change was owed to an adequate representation of winter accumulation distribution by means of extensive GPR measurements.

Mass balance observations and reconstruction for Batysh Sook Glacier, Tien Shan, from 2004 to 2016

“…A good estimate of the accumulation gradient seems to be very difficult because of insufficient data to better constrain the spatial distribution of snow. Several studies (e.g., Sold et al, 2016;Helfricht et al, 2012Helfricht et al, , 2014 show that an improvement in the mass balance determination is possible through the combination of conventional mass balance data and data obtained by new methods such as helicopter-borne Ground Penetrating Radar or Light Detection And Ranging (LiDAR) measurements. Such data also enables an improvement in the interpolation of the accumulation distribution.…”

“…The uncertainty related to the extrapolation in the ablation area (σ abl_area ) is estimated from the one-sigma confidence intervals of the regression coefficient and leads to a value of σ abl_area = ±0.12 m w.e. a −1 (e.g., Sold et al, 2016). The combination of these different uncertainties of the profile method results in a total annual uncertainty of σ profile = ±0.28 m w.e.…”

“…The latter is linked with the subjective interpretation and manual drawing of the contours by the observer (Sold et al, 2016). Here, the respective uncertainty is assessed with using a "round-robin" test.…”

The bedrock topography of Gries- and Findelengletscher

“…Since penetration depth of electromagnetic waves generally decreases with higher frequencies, and due to the properties of ice, frequencies between 1 and 1000 MHz are typically used (Yelf, 2007). The choice of the frequency directly relates to the spatial resolution with which individual reflectors can be detected (Van Dam, 2012). On temperate glaciers, signal attenuation can be important and can significantly affect the reliability of measurements (Lapazaran et al, 2016a, b;Martín-Español et al, 2016).…”

A reanalysis of one decade of the mass balance series on Hintereisferner, Ötztal Alps, Austria: a detailed view into annual geodetic and glaciological observations

“…For extrapolating point data into reasonable patterns of mass balance, the contour line method uses expert knowledge. Based on Sold et al (2016), we estimate a respective uncertainty of ±0.15 m w.e. a -1 for Hintereisferner.…”