Crystalline structure and physical properties of ship superstructure sprayice

In February and March 1990 the US Army Corps of Engineers Cold Regions Rese arch and Engineering Laboratory (CRREL) made measurements of superstructure ice on a US Coast Guard cutter in the Bering Sea. Twenty-three ice samples were removed from bulkheads, decks and icicles during two icing events. Ic e crystal measurements included crystal size, shape, orientation, brine-poc ket location, size and shape, internal layering, and air-bubble sizes. Ice property measurements included salinity, density and temperature, with comp uted estimates of air and brine volume. This paper describes crystal and ph ysical properties of the accreted ice and their relationship to ice sample position oil the ship. Texturally, accreted ice resembled frazil ice that forms from the consolida tion of freely nucleated ice crystals in sea water. This resemblance is als o reflected in bulk salinities, ranging from 24 parts per thousand to 7 par ts per thousand, compared with frazil formed during the initial stages of f reezing of sea water, where bulk salinities can exceed 10 parts per thousan d. Crystalline structures of accreted ice ranged from rounded to polygonal. Generally, rounded crystals would be expected for ice formed from sea-spra y droplets, polygonal crystals may be attributed to thermally driven modifi cation. No trend towards reorientation of crystallographic c-axes in either freshly accreted or thermally modified ice was observed. Mean crystal sixe s ranged from 0.56 mm to 1.15 mm, with even larger crystals in icicles. Ice salinity averaged ca. 12 parts per thousand on bulkheads and ca. 21 par ts per thousand on decks. Ice densities ranged from 0.69 to 0.92 Mg m(-3) a nd mere generally higher on decks. Bulkhead ice had larger computed total p orosity and air volume and lower brine volume than deck ice. Samples taken from decks and bulkheads generally compared well with Russian and Japanese measurements.