ИСТИНА

Frontal ablation (the sum of ice loss through calving and submarine melt) of tidewater glaciers and ice caps in the Russian Arctic is poorly known. Meanwhile it is an important component of their mass balance, and its knowledge is strongly required when considering the iceberg risk in off-shore industrial activities. Study area is located in three archipelagoes of the Russian Arctic with total glacierized area 51,591 km2, including Novaya Zemlya (NZ) 22,128 km2, Franz Josef Land (FJL) 12,762 km2, and Severnaya Zemlya (SZ) 16,701 km2 [1]. To assess the frontal ablation the data on ice thickness, ice velocity and glacier front change are required. Data on ice thickness of 31 glaciers (12 on NZ, 11 on FJL, and 8 glaciers on SZ) were obtained during our airborne 20 MHz RES campaigns in 2014–2016. Data on variations of glacier fronts from 2001 to 2016 were extracted from Landsat satellite imagery. Glacier surface velocities from 2014 to 2016 were based on feature tracking on repeat Landsat-8 imagery using COSI-Corr package and from GoLIVE v.1 [2] data set combined with continuous records from seven GPS beacons installed on five glaciers. ArcticDEM data on glacier ice surface combined with RES ice thickness data were used to compile glacier bedrock maps and transects. Frontal ablation is estimated for each glacier as a sum of the ice flux through a fixed fluxgate above the position of the calving front, and the ice volume change in the terminus below the fluxgate due to advance or retreat. The spatially fixed fluxgate is defined approximately perpendicular to the ice flow, 250–1500 m upglacier from the actual calving front. The depth-averaged speed is extracted from the surface velocity field in increments of 25 m along the fluxgate and weighted by a correction factor 0.9. The ice thickness is extracted in the same points from the ice thickness maps or transects. Radar two-way time data were converted to ice thickness using radio wave propagation speed 168 m mcs􀀀1. We do not include in our estimations all glaciers without RES data, and also the surging western basin of the Vavilov Ice Cap and disintegrating Matusevich Ice Shelf (both SZ). Mean ice thickness at glacier fronts is in average: from 60 at eastern coast to 105 m at western coast of NZ; 107 m on FJL, and 117 m on SZ. Maximum ice thickness at glacier front has the Inostrantsev Glacier on NZ: 216 m in average (maximum _400 m) (Fig.1). Frontal ablation rate of RES surveyed glaciers is assessed as: 2.05 km3 a=1 on NZ (12 glaciers) including 0.51 km3 a-1 on eastern coast (4 glaciers) and 1.54 km3 a􀀀1 on western coast (8 glaciers); 1.66 km3 a-1 on FJL (11 glaciers); and 3.07 km3 a􀀀1 on SZ (8 glaciers). Share of terminus position changes in total frontal ablation is: 28% on NZ (32% eastern coast and 26% western coast), 27% on FJL, and 24% on SZ. Our assessment of annual frontal ablation of outlet glaciers in the Russian Arctic as 7 km3 of ice is a minimal one, because it based on the data set of only 31 RES-surveyed glaciers. This set covers less than a quarter of calving glaciers on NZ and SZ, and even less on FJL. But a simple increasing of our assessment in proportion to the number or area of all calving glaciers will not give the correct overall estimate. Input of studied glaciers in our assessment is very unequal. The following 6 glaciers provides nearly 60% of frontal losses in our estimate: No 8, No 7 and Issledovateley Glaciers on SZ, Inostrantsev and Vershinskiy Glaciers on NZ, and Znamenitiy Glacier on FJL (1.04, 0.63, 0.76; 0.71, 0.3; and 0.69 km a-1, respectively). Terminus retreat is an important component, constituting near a quarter of the frontal ablation of studied glaciers. Figure 1. Inostrantsev Glacier, Novaya Zemlya: a) ice surface velocity (m a-1); b) ice surface (m a.s.l.); c) ice thickness (m), d) bedrock elevation (m). Acknowledgments. This study is supported by the Russian National Foundation, grant 14-37-00038, and the Arctic Program of the Presidium of the Russian Academy of Sciences. ArcticDEM is provided by the Polar Geospatial Center under NSF OPP awards 1043681, 1559691 and 1542736, and Landsat images is a making available their COSI-Corr. References 1. RGI Consortium, 2017, Randolph Glacier Inventory (RGI) - A RDataset of Global Glacier Outlines: Version 6.0. Technical Report, Global Land Ice Measurements from Space, Boulder, Colorado, USA. Digital Media. DOI: https://doi.org/10.7265/N5-RGI-60. 2. Scambos T., Fahnestock M., Moon T., Gardner A., Klinger M. Global Land Ice Velocity Extraction from Landsat 8 (GoLIVE), Version 1. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. 2016. doi: http://dx.doi.org/10.7265/N5ZP442B Accessed on June 14, 2017.