Petrographic and Salinity Characteristics of Brackish Water Ice in the Bay of Bothnia
COLD REGIONS RESEARCH AND ENGINEERING LAB HANOVER NH
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Field observations made during the March 1988 BEPERS Bothnian Experiment in Preparation for ERS-1 remote sensing experiment included measurements of the snow and ice thickness, temperature, salinity and crystal structure profiles of the different types of brackish ice that form in the Bay of Bothnia. Both undeformed fast ice and ice that had formed under more disturbed conditions were sampled. Ice thicknesses varied from 36 to 64 cm in the bay to the east of Umea, Sweden, with somewhat thicker ice 76 cm occurring in the northernmost, nearly fresh water areas of the Bay of Bothnia. Three major ice crystal types or textures were identified-granular, transition and columnar ice-with the amount of each depending on the level of disturbance in the water column. At seven of the sixteen sites investigated, granular mainly frazil ice was the dominant component. At six of the remaining nine sites, columnar- congelation ice was the predominant ice crystal type. A mix of transition and transition-congelation ice types dominated the structure of the remaining three sites. At all but two sites the bottom ice consisted of congelation ice, which in many instances exhibited the ice plate and brine layer substructure so typical of arctic sea ice. A variety of c-axis fabrics were observed in the columnar-congelation ice, including random, vertical and horizontal planar orientations. Aligned c-axes were observed at several locations, but in most cases there was no obvious pattern to the geographic arrangement of these fabrics. Surface water salinities ranged from 3.6 to 4.1 o except at the northernmost sites near Tornio, where essentially riverine fresh water was present. Bulk Bay of Bothnia, Ice growth, Ice structure, Radar characteristics. Brackish ice, Ice salinity, Ice temperature.
- Snow, Ice and Permafrost