The size and frequency of icebergs and bergy bits derived from tidewater glaciers in Kongsfjorden, northwest Spitsbergen

Julian A. Dowdeswell, Carl Fredrik Forsberg
1992 Polar Research  
1992: The size and frequency of icebergs and bergy bits derived from tidewater glaciers in Kongsfjorden, northwest Spitsbergen. Polar Research 11(2). 81-91. Tidewater glaciers constitute over loo0 or 20% of the coast of Svalbard. The dimensions and frequency of the occurrence of icebergs and bergy bits produced from these tidewater glaciers in Kongsfjorden, northwest Spitsbcrgen. were measured during the summers of 1991 and 1992. In 1991, 35-40% of 275 observed icebergs and bergy bits were c0.5
more » ... ergy bits were c0.5 m wide. and I m in height. The largest observed freeboard was 6m. In 1992, small icebergs were significantly less common. 50% of the observed icebergs were >10m in width and >2 m in freeboard. This is interpreted to be the result of a major calving event prior to the 1992 observations. Side-scan sonar data on sea floor morphology showed frequent scouring by iceberg keels to a depth of 35 m, but no scouring below 40 m, thus defining the maximum iceberg keel depth and the depth to which sediment reworking by these keels occurs. Calculations of the melt rate of icebergs allows an estimation of the life expectancy of icebergs calved into Kongfjorden. Melting by forced convection lies between approximately 0.1 and a maximum of 1.0 m d-'. depending on iceberg relative velocity, size and water temperature. Melting linked to wave action is also approximately 0.S1.0 m d-I. These calculations imply that icebergs of the dimensions commonly observed in Kongsfjorden will seldom survive travelling beyond the fjord mouth. Radar observations of iceberg occurrence from FS POLARSTERN during its summer 1991 circumnavigation of Svalbard also showed that no larger icebergs were escaping heyond the mouths of the major fjords of western and northern Spitsbergen. Iceberg derivation from Spitsbergen fjords is therefore not likely to be an important mechanism for sediment rafting and deposition on the continental shelf and in the decp ocean. but it is of significance to local fjord sedimentation. Comparison with evidence on iceberg dimensions from the Barents Sea and an East Greenland fjord shows that the larger icebergs there are derived from parent ice masses with quite different characteristics than those calving into the Spitsbergen fjords.
doi:10.3402/polar.v11i2.6719 fatcat:kga2vgau7zgzpcuh4q7brxtefu