ALBERT

Description: The Cordillera Darwin Icefield in Tierra del Fuego experienced important mass losses during the last decades. Yet it is difficult to associate the recent loss to atmospheric changes as in-situ observations of climatic conditions and glacier mass balances are scarce due to the difficult accessibility and the harsh weather conditions in that area. Under these challenging conditions, we investigate strategies for calibration of surface mass balance models in the Monte Sarmiento Massif, western Cordillera Darwin. This study aims to identify best practices for regional scale application as well as to assess the influence of melt-model complexity.Applied calibration strategies range from a local single-glacier calibration to a regional calibration with the inclusion of a snowdrift parametrization. Furthermore, we apply four models of different complexity ranging from an empirical degree-day model to a fully-fledged surface energy balance model. This way, we examine the model transferability in space, the benefit of including regional mass change observations as calibration constraint and the advantage of increasing melt-model complexity. In-situ measurements comprise ablation stakes, ice thickness surveys and meteorological records at one glacier. Satellite remote sensing provides surface velocity and geodetic elevation changes for the entire region. Performance of simulated surface mass balance is validated against geodetic mass changes and stake observations.Results show that spatially transferring mass balance models is challenging and can produce distinctly biased estimates. The use of remotely sensed regional observations can significantly improve model performance. Snowdrift has an important impact on the surface mass balance in the Cordillera Darwin.

Description: The Antarctic Peninsula Ice Sheet (APIS) has become a significant contributor to sea-level rise over the last decades. It is crucial to estimate the ice discharge from the APIS outlet glaciers to understand the overall mass balance of Antarctica. In this study, we calculated the ice discharge from the APIS outlet glaciers north of 70 ºS employing four widely used ice-thickness reconstructions. By using a common surface velocity field and flux gates, we found that the estimation of the total volumetric ice discharge between 2014 and 2017 ranges from 52 to 134 km〈sup〉3〈/sup〉/y, with a mean of 85 ± 37 km〈sup〉3〈/sup〉/y. The significant differences between the results of the total ice discharge, as well as a multi-model normalized root-mean-squared deviation of 1.20 for the whole data set reveal large differences and inconsistencies between the ice-thickness models. This highlights a fundamental issue: the limited availability of accurate ice-thickness measurements and the challenges faced by current models in reconstructing the distribution of ice-thickness in this complex region.

Description: Glacier calving is an essential process for the ablation of marine-terminating glaciers. The calving front position is needed to compute the glacier surface area and the total frontal ablation rate. With the increasing number of satellite observations, the calving process is observable with a higher temporal resolution. We avoid the labour-intensive annotation of the calving front in satellite images by training a neural network that delineates the calving fronts automatically. We use a deep learning framework called nnU-Net (no new U-Net) that adapts the widely used segmentation network U-Net to a given dataset. We evaluate the method on a benchmark dataset called CaFFe (CAlving Fronts and where to Find thEm). The dataset is conceived to compare different methods for calving front detection and glacier zone segmentation from Synthetic Aperture Radar images. In the end, we examine season and satellite's impact on the calving front detection quality.

Description: Some of the highest specific mass change rates in Antarctica are reported for the Antarctic Peninsula. However, the existing estimates for the northern Antarctic Peninsula (〈70°S) are either spatially limited or are affected by considerable uncertainties. Within this study, the first assessment of the geodetic mass balance throughout the ice sheet of the northern Antarctic Peninsula is carried out employing bi-static SAR data from the TanDEM-X satellite mission. Repeat coverages from austral-winters 2013 and 2017 are employed. An overall coverage of 96.4% of the study area by surface elevation change measurements is revealed. The spatial distribution of the surface elevation and mass changes points out, that the former ice shelf tributary glaciers of the Prince-Gustav-Channel, Larsen-A&B, and Wordie ice shelves are the hotpots of ice loss in the study area, and highlights the long-lasting dynamic glacier adjustments after the ice shelf break-up events. The highest mass change rate is revealed for the Airy-Seller-Fleming glacier system and the highest average surface elevation change rate is observed at Drygalski Glacier. The comparison of the ice mass budget with anomalies in the climatic mass balance indicates, that for wide parts of the southern section of the study area, the mass changes can be partly attributed to changes in the climatic mass balance. The previously reported connection between mid-ocean warming along the southern section of the west coast and increased frontal glacier recession does not repeat in the pattern of the observed glacier mass losses, excluding Wordie Bay.

Description: Polar research is an interdisciplinary and multi-faceted field of research ranging from history to geology and geophysics to social sciences and education. Thus, several different universities and institutions within Germany participate in polar research. The seminar series POLARSTUNDE, organized by the German Society for Polar Research (Deutsche Gesellschaft für Polarforschung) and the German National Committee of the Association of Polar Early Career Scientists (APECS Germany) regularly features different topics of German polar research. Although initially a “pandemic solution”, the seminar series has established itself as a valuable and highly successful part of the German polar research landscape. The seminar series was held in German and was aimed at both scientists and the general public. This article addresses the first season of POLARSTUNDE and provides (1) comprehensive summaries of the talks and (2) insight into the planning and execution from an organizational point of view.