Лëд и снег (Aug 2020)
Comprehensive study of old hummocks in the Arctic Ocean
Abstract
In May 2015, the old hummock located to the North of the Bennett island (the East Siberian Sea) was investigated using several methods, among which were water thermal drilling, tachometric and sonar surveys, underwater video recording, as well as techniques to determine the strength and physical properties of ice. It was found out that only a combination of different methods provides a way to correctly estimate the main morphometric characteristics of a large ice formation and to determine its volume and mass. Analysis of the internal structure of the hummock, obtained by the water thermal drilling with a record of the drilling rate on the logger, made it possible to reveal a composite character of the ice formation (the hummock consisted of two fragments – the large old one and the smaller first-year piece) and to estimate approximately its age (3–4 years). Comparison of the main morphometric characteristics of the old hummock with the average values of first-year hummocks, investigated in the same area and the time, showed that the old hummock had significantly greater geometric parameters: its volume and mass exceeded similar parameters of the average younger formation by factors 5.6 and 5.8, respectively. This significant difference allows suggestion that the reason is not the age but a composite structure of the old formation. The average thickness of the consolidated layer of the old hummock equal to 4.6 m is almost twice larger than similar parameter of a first-year hummock (2.33 m) while the average value of the thickness in the old part of the old hummock (5.22 m) is larger than that of a young one by the factor 2.2. Note also, that the old hummock is characterized by almost complete smoothness (impossible to separate individual blocks) and minimal porosity (1%) of its ice. The salinity and density of the ice composing the frontal part of the old hummock is much smaller than in first-year hummocks. The average density of ice in the old hummock, determined analytically from the buoyancy condition, was equal to 896 kg/m3, while the average density of ice in the first-year hummocks, determined from measurements, – 917 kg/m3.
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