| Summary: | In May 2015, a comprehensive study of an old ice ridge was carried out to the north of Bennett Island in the East-Siberian Sea with application of water thermal drilling, tachometric and sonar surveys, video survey by the underwater device and methods for determination of the ice strength and physical properties. It is shown that only a combination of different methods allows us to obtain a correct assessment of the main morphometric characteristics of a large ice feature and determine its volume and mass. An analysis of ice ridge internal structure parameters obtained by the method of water thermal drilling with the drilling rate record to a logger made it possible to reveal a composite character of the ice feature (the ice ridge consisted of a larger old fragment and a smaller first-year fragment) and approximately assess its age (3-4 years). A comparison of the main morphometric characteristics of an old ice ridge and the average values of first-year ice ridges, investigated in the same region at the same period of time showed the old ice ridge to have significantly greater geometric parameters. The old ice ridge volume and mass were greater compared to the average first-year ice ridge by 5.6 and 5.8 times, respectively. Such significant advantage of the old ice ridge is likely to be determined by the composite character of the ice feature rather than by its age. The average for the entire composite ice ridge thickness of the consolidated layer (4.6 m) is almost two-fold greater than the average thickness of the consolidated layer in the first-year ice ridges (2.33 m), and the average value of the consolidated layer in the ice ridge old part (5.22 m) is 2.2 times greater than in first-year ice ridges. An old ice ridge is characterized by an almost complete flatness (without any possibility to identify some separate blocks) and minimal sail porosity (1 %). The salinity and density of ice comprising the old ice ridge sail were much lower than in first-year ice ridges. The sail/keel ratio is greater on average ...
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