Changes of glacier facies on Hornsund glaciers (Svalbard) during the decade 2007-2017

Changes in glacier facies (glacier zones), such as firn or superimposed ice (SI), are good indicators of glacier response to climate change. They are especially important for fast-warming Svalbard, where only a few glaciers are under glaciological mass balance monitoring. This paper presents a first study of changes of glacier facies extent for three tidewater glaciers located in southern Spitsbergen (Svalbard) and it is based on both satellite remote sensing and terrestrial data analysis, covering two time spans: 2007-2017 for Hansbreen and 2012-2017 for Storbreen and Hornbreen. Satellite remote sensing analysis include unsupervised classification of Synthetic Aperture Radar (SAR) data from both decommissioned (ENVISAT ASAR) and modern satellite missions (RAD-ARSAT-2, Sentinel-1). The results of the SAR classification are compared to the information on glacier zones retrieved from terrestrial data, i.e. shallow cores and visual interpretation of 800 MHz Ground Penetrating Radar (GPR) profiles. In addition, a novel application of the Internal Reflection Power (IRP) coefficient as an objective method of distinguishing glacier zones based on GPR data is discussed. Changes in glacier facies areas over time are analysed, as well as their correlation to Hansbreen's mass balance. The main finding of the study is that firn and SI of Hansbreen, Storbreen and Hornbreen significantly decreased over the study period. For example, due to continuous negative mass balance between 2010 and 2017, the contribution of firn area to Hansbreen's total area decreased ca. 14% (cumulative firn area loss during that time: similar to 45%) whereas since 2012 SI has not been distinguished as a vast area on this glacier. In addition, an east-west gradient of firn area loss was observed as a result of differences in local climate conditions. Therefore, for the common time span (i.e. 2012-2017) Hansbreen recorded a ca. 12% loss of firn contribution to glacier area whereas Hornbreen recorded ca. 9%. Finally, application of the IRP coefficient as an objective method of glacier zones discrimination by GPR data gave very good results, so the method is recommended for future analysis of glacier zones instead, or as a support, to popular visual interpretation of the GPR profiles.