Physical properties of summer sea ice in the Fram Strait, June-July, 1984

Abstract : Most of the ice sampled was multi-year; it is estimated to represent at least 84% by volume of the total ice discharged from Fram Strait during June and July. Thicknesses and other properties indicated that none of the multi-year ice was older than 4 to 5 years. Snow cover on the multi-year ice averaged 29 cm deep while that on first-year averaged only 8 cm. Much of this difference appears to be the result of enhanced sublimation of the snow on the thinner first-year ice. Salinity profiles of first-year ice clearly show the effects of ongoing brine drainage in that profiles from cores drilled later in the experiment were substantially less saline than earlier cores. Bulk salinities of multi-year ice are generally much lower than those of first-year ice. This difference furnished a reliable means of distinguishing between the two ice types. Thin section examinations of crystal structure indicate that about 75% of the ice consisted of congelation ice with typically columnar crystal structure. The remaining 25% consisted of granular ice with only a few occurrences of snow ice. The granular ice consisted primarily of frazil, found in small amounts at the top of floes, but mainly observed in multi-year ridges where it occurred as the major component of ice in interblock voids. The horizontally oriented crystal c-axes showed varying degrees of alignment, from negligible to strong, in which the alignment direction changed with depth, implying a change in floe orientation with respect to the ocean current at the ice/water interface during ice growth.

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