In-Situ Measurement of Elastic Properties of Sea Ice

Abstract

Sea ice, a distinguishing feature of all Arctic waters, is a complex polycrystalline solid layer (1) that forms at the boundary between the atmosphere and the oceans when the surface temperature of the sea falls below, approximately, -2°C. Dynamic environmental conditions introduce significant variability into this layer over many length scales of interest to the underwater acoustian (from millimetres to kilometres). Arctic pack ice, for example, is a conglomerate consisting of multiyear floes, refrozen leads of first year ice and jumbled masses of ice blocks known as pressure ridges. The first year (annual) ice has a characteristic vertical layering in which relatively large pure ice crystals, of the order of centimeters, grow vertically between planes containing precipitated salts, brine and trapped air; it is therefore quite saline (5–6‰). Whereas, multiyear ice, or ice that has survived at least one melt season, becomes highly porous during the warm summer months allowing the nearly fresh surface melt water to flush through the ice to the sea below. As a result of this process, multiyear ice is usually less saline (2–3‰), has smaller ice crystals and is characterized by a horizontal layering representing the annual cycles.