Accession Number : AD0745631

Title :   Thermal Tension Cracking in Sea Ice: A Source of Underice Noise,

Corporate Author : DEFENCE RESEARCH ESTABLISHMENT PACIFIC VICTORIA (BRITISH COLUMBIA)

Personal Author(s) : Milne,A. R.

Report Date : 24 JAN 1972

Pagination or Media Count : 17

Abstract : A summary is given of the important observations that relate the rheological properties of sea ice to the occurrence of surface tension cracks and explain how the noises produced by myriad surface cracks are observed under the ice. Ice-cracking noise is expected where the surface of the sea ice is cold and has a sufficiently low salinity to approximate a brittle solid. This condition is more likely to occur in seas covered by a high percentage of multi-year ice and where wind-making in leads was absent when the seas congealed. The acoustic water waves observed from crakc-excited plate waves are described and two examples of single-frequency Crary wave arrivals are shown. A mechanism is postulated to explain the tendency for regularity in the spacing of pressure ridging in the Arctic Ocean. Thermal pre-stressing at the ice surface, added to flexural stresses caused by wind-induced flexural-gravity standing waves, can produce significant tensile stress maximums at antinode spacings. (Author)

Descriptors :   (*SEA ICE, THERMAL STRESSES), ARCTIC OCEAN, CRACKS, TENSILE PROPERTIES, UNDERWATER SOUND, CANADA

Subject Categories : Physical and Dynamic Oceanography
      Snow, Ice and Permafrost

Distribution Statement : APPROVED FOR PUBLIC RELEASE