Satellite map series of long-term elevation changes on Eurasia's northernmost ice caps

Global warming leads to glacier melt and decline. But, there exist glaciers and ice caps which grow under present climatic settings. In the High Arctic there are many growing glaciers and the glacier change pattern remains commonly heterogeneous. The explanation of main causes for this heterogeneity is not trivial as, in many cases, such anomalies cannot be explained by local orographic, topographic, oceanographic and/or rheological conditions, and some insular ice caps seem to increase their volumes for no apparent reasons. Causal analysis and interpretation of glacioclimatic variations in the Arctic became possible after new series of satellite image maps showing the mesoscale distribution of glacier elevation changes in the heterogeneous
 field of gravity were generated using space-borne altimetry, interferometry and gravimetry data. The present paper describes a new suite of seventeen maps representing glacier elevation changes in the Eurasian High Arctic in the period from the 1950s to the 2010s with 50-m grid in the UTM projection (Zones 34N ??? 57N, WGS 84) at 1:200 000 and, sometimes, 1:100 000 scale. The area covered by our maps extends for approx. 2.300 km from Svalbard in the west through Franz Josef
 Land, North Novaya Zemlya and Severnaya Zemlya in the north to De Long Islands in the east thus comprising the most distant and least studied ice caps, 25 to 2500 km??? in extent, in the northern periphery of Eurasian shelf seas. The overall glacier change mapping in the study region including quantification of mass balance characteristics was performed by comparing reference elevation models of study glaciers derived from the available topographic maps showing the glacier state as in the 1950s with modern elevation data obtained from satellite ERS and/or TanDEM-X radar interferometry and ICESat / CryoSat altimetry. Modern outlines of maritime glacier faces were corrected with the high-resolution optical quicklook imagery obtained from WorldView and Terra ASTER satellites. The vertical accuracy of glacier change maps proved on several ice caps was given as ??? 0.3 m/a rms. In addition to glacier elevation changes, main ice divides, glacier borders and main shallows offshore the maps also show the multi-year equilibrium line, present heights of ice coasts, frontal velocities of tidewater outlets and free-air gravity anomaly isolines derived from GOCE R3 data. All maps can be accessed at http://dib.joanneum.at/MAIRES/.
 The resultant maps allowed a precise measurement of glacier changes in linear, areal and volumetric terms to be performed. The size of accumulation and ablation areas was determined in semi-automatic mode. The multi-year orographic ELA measured in the maps was 50 to 150 m lower than previously published estimates. The cumulative mass budget in the study region remained negative while individual rates of volume change varied from -0.07 km???/a to +0.06 km. Positive
 values of average mass balance with the maximum accumulation signal of approx. 1.4 m/a were determined on Ahlmanfonna, Northern, Vostock-2, Windy, Ushakova, Aerosjemki, Fedchenko and Toll ice caps. The research revealed strong positive distance-weighted correlation between the magnitude of gravity anomalies and gravity gradients on one hand and glacier elevation changes on the other, while it was noted that the correlation decreases in humid and mountainous areas. Further
 statistical analysis of long-term records of daily precipitation obtained from 38 meteorological stations in the study region showed that the precipitation amount, annual number of precipitation events and the intensity of snow accumulation are closely dependent on the strength of gravity anomalies nearby. Finally we discuss the rate of glacial isostatic adjustment in the region using the results of PS interferometry and provide some analytical explanations based on the concept of adiabatic lapse rate, meteorological perturbations and deviatoric precipitation in arctic deserts with anomalous gravity.