Abstract. We observed a tsunami wave near the glacier front in the Temple Fjord (Spitsbergen). Two temperature and pressure recorders were deployed on a wire from the ice approximately 300 m from the glacier front. A pressure recorder was located under them on the bottom. The vertical displacement of the ice was approximately 30 cm and the period of the tsunami wave was 90 s. We attribute the generation of this wave to the displacement of the glacier similarly to the landslide tsunami generated by the motion of a block of rocks down the sloping bottom. The glacier motion also generated a short-period (12 s) deformation wave in the ice cover. The measurements allowed us to estimate the wave number of these waves and the Young's modulus of the ice.

A method to estimate the flexural stiffness and effective elastic modulus of floating ice is described and analysed. The method is based on the analysis of water pressure records at two or three locations below the bottom of floating ice when flexural-gravity waves propagate through the ice. The relative errors in the calculations of the ice flexural stiffness and the water depth are analysed. The method is tested using data from field measurements in Tempelfjorden, Svalbard, where flexural-gravity waves were excited by an icefall at the front of the outflow glacier Tunabreen in February 2011.

A theoretical model for propagation of internal waves under an ice cover is developed. The sea water is considered to be inviscid, non-rotating, and incompressible and the Brunt-Väisälä frequency is supposed to be constant. The ice is considered of uniform thickness, with constant values of Young's modulus, Poisson's ratio, density and compressive stress in the ice. The boundary conditions are such that the normal velocity at the bottom is zero and, at the undersurface of the ice, the linearized kinematical and dynamic boundary conditions are satisfied. We present and analyze explicit solutions for the internal waves under the ice cover and the dispersion equations. It is shown that when the frequency is near, but smaller than the Brunt-Väisälä frequency the ice deflections can be considerable. The theoretical results are compared with experimental data for the Arctic regions. Keywords : ice deflections; internal waves; Brunt-Väisälä frequency 1 Introduction The influence of the ice cover on the propagation of internal waves is practically important, but poorly studied. It is a common assumption that the rigid lid approximation that filters out the surface mode and adequately describes the properties of internal waves should also be valid in the case, where the free surface is substituted by an ice cover. Since the vertical velocity at the surface is zero in the approximation, the internal waves cannot be recorded on the basis of fluctuations of the ice cover. Such a conclusion, however, contradicts the data from previous observations [Czipott et al. (1991); Smirnov (1972); Smirnov, Savchenko (1972); Smirnov et al (2002)]. For example, oscillations of the ice cover recorded on the "Severnyi Polyus-20" ice drifting station in 1970 [Smirnov (1972)] cannot be related to surface flexural-gravity waves. They were interpreted as manifestations of internal waves in conditions with clearly manifested interleaving of waters in the Arctic Basin. Therefore, it is necessary to develop a more specific theory of internal waves applied to the waves in a stratified ocean covered with ice. In this paper we develop a theory of internal waves under an ice cover at constant Brunt-Väisälä frequency. 2 Formulation of the problem Let us consider water motion under an ice cover, which is considered to be a thin elastic plate of constant thickness floating at the sea surface. We will consider wave motions as small deviations from the hydrostatic equilibrium state at zero background currents in the ocean. Then, the linearized system of equations of motion for non-rotating stratified fluid is written as [Pedlosky (2003)]: 0 1 P t       u ; 0

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