EVIDENCE FOR FLOATING ICE SHELVES IN FRANZ-JOSEF-LAND, RUSSIAN HIGH ARCTIC

Examination of digital Landsat TM and MSS imagery of Franz Josef Land, Russian High Arctic, reveals a number of ice caps with apparently very low surface gradients at their seaward margins. The largest of these low gradient areas is 45 kM2. The areas are dynamically a part of the parent ice mass, and have a marked break of slope at their inner margins. They generally occur in protected embayments and often have relatively deep water offshore. The presence of deep inter-island channels (up to 600 m) in the archipelago also suggests that deglaciation after the last glaciation may have proceeded rapidly due to enhanced iceberg calving. Tabular icebergs (maximum observed length 2.3 km) are produced from several of the low gradient ice cap margins today. Ice surface profiles, derived from analysis of vertical aerial photographs, show slopes of 0.5-degrees on these features, as compared with 3.5 to 50 on other ice caps. At least some are likely to be floating ice shelves. They have similar ice surface gradients to a known ice shelf on Severnaya Zemlya. There is no requirement for deep water to occur beneath these features, but simply that they become buoyant over a significant part of their base. Glacier thinning, due to reduced mass balance since the termination of the Little Ice Age, may have contributed to the presence of these features. An origin for some of these low gradient margins by deformation of an unlithified substrate cannot be ruled out. Field radio-echo experiments could be used to test the interpretation of these features as ice shelves.