Crystal size and orientatio~i in ice sheets frozen under one-climensional c o o l i~~g from melts of pure water or melts containing traces of 01-ganic additives were st~~cliecl ~~s i l i g a polariscope with a universal staxe. The surface layer is found to consist of crystals \\lith nearly vertical optic axes. Horizontal sections cut a t \,arious depths show a gradual change of the mean orientation of the optic axes to\\rards the horizontal. 'l'he change to horizontal inclinations is almost cornpletecl a t depths of 4 or 5 cm. ~~ncler the freezing conclitions usecl, and occurs more rapidly \\.it11 the melts containing aclclitives. With aclcliti\.es t-he ice sheet sho\\ls another feature also, a trarlsition layer about 0.6 cm. belo\\. the surface. I n this layer the crystals are rn~lch smaller than in the surface layer abo\,e them ancl the number of crystals esteriding through this layer is small.An explanation of the observations is on'ered, in terms of preferred growth of an ice crystal in planes pcrpenclicular to the optic axis. This provicles a mechanism permitting inore rapid growth of crystals \\,it11 iiiclinecl axes.1Manuscript
No abstract
This preliminary study is based mostly on work done at a shore station in Shippegan, N.B., during the winter of 1956–57, with some data from an icebreaker expedition in the summer of 1956. The Shippegan site had unrafted ice, tides of 5 feet or less, and negligible fresh-water runoff. The thickness of the ice was about proportional to the square root of the freezing exposure. Tritium dating of sea ice is an unsatisfactory method because of variable tritium concentration in Arctic waters. The jaggedness of ice crystals is suggested as a measure combining effects of age and thermal regime. Measurements of specific gravity, salinity, electrical resistivity, and permeability profiles all show progressive changes in annual sea ice throughout the winter. The tensile strength of sea ice at −20 °C was around 200 to 500 p.s.i., at various angles to the grain. For fresh-water ice, with stress parallel to the grain, it was in the range 500 to 1000 p.s.i. Shear strengths, with the shear plane parallel to the grain, were 80 to 160 p.s.i. for sea ice at −20 °C and 160 to 280 p.s.i. for pond ice, also at −20 °C.
No abstract
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