Variations In Mechanical Properties Within A Multi-year Ice Floe

Abstract

Ice cores taken from several locations on a multi-year floe show significant horizontal and vertical variations in their physical properties. Composite plate theory was used to determine the flexural rigidity from these ice properties. Rigidities calculated using brine volume alone and using both brine and air volumes show a srong dependence on ice thickness. thickness to determine rigidities over a small area of the floe shows large variability due to major changes in thickness. INTRODUCTION Using ice It is well known that the physical properties of sea ice vary significantly with depth. systematic variation of entrapped brine and temperature in a growing first-year i e s eet has been documented in a number of studies. 11''3'' The temperature profile is typically linear, increasing with depth from the cold surface to the freezing point at the bottom of the ice sheet. As a result, the salinity profile is typically C-shaped, with the highest salinities occurring at the top and bottom of the ice sheet. profiles, of course, change dramatically with the warming of the ice sheet during summer. The physical properties of multi-year ice also vary with depth. Due to the unique evolutionary process of each multi-year ice floe, however, the variation is not nearly as predictable as that for first-year ice sheets. Salinities are generally very low near the surface because of flushing that occurs during the warm summer period. with depth, although the profile may be erratic or discontinuous, depending on the history of the floe. Variations in the crystal structure and the presence of deformed ice affects the distribution of the saline brine within the ice. For instance, granular ice may trap and hold more brine because a system of brine drainage channels cannot be easily established. If columnar ice has been deformed such that the well established drainage channels are inclined (as in the tilted blocks of a ridge or rubble field), normal drainage systems are interrupted and the brine drainage may be enhanced or d'minished. Recent investigations in the Fram Strait'" confirm that there are substantial variations in the vertical property profiles among multi-year floes. Properties also vary significantly within the same multi-year floe, as was clearly pointed out by Cox and Weeks,* who found large vertical and horizontal variations of salinity across a small area of a multi-year floe. In addition to the significant variation in the physical properties of the floe both vertically and horizontally, 5hg thickness of multi-year floes varies considerably. ' Large variations in thickness are caused by the incorporation of deformed ice, namely ridges that have consolidated by weathering and have become an integral part of the floe. Small thickness undulations are stimulated by surface melt ponds, which can cause The relatively