A comprehensive analysis of the morphology of first-year sea ice ridges

摘要

A review of the morphological properties of over 300 full-scale floating first-year sea ice ridges has been made, including measurements from 1971 until the present time. Ridges were examined from the Bering and Chukchi Seas, Beaufort Sea, Svalbard waters, Barents Sea and Russian Arctic Ocean for the Arctic regions; and from the Canadian East Coast, Baltic Sea, Sea of Azov, Caspian Sea and Offshore Sakhalin for the Subarctic (or temperate) regions. Grounded ridges were excluded. A wide catalogue comprising the ridge thicknesses (sail, keel and consolidated layer), widths and angles as well as the macroporosity and the block dimensions is provided. The maximum sail height was found to be 8 m (offshore Sakhalin), and the mean peak sail height was 2.0 m, based on 356 profiles. The mean peak keel depth is 8.0 m, based on 321 profiles. The relationship between the maximum sail height, h_s, and the maximum keel depth, h_k, for all ridges is best described by the power equation h_k = 5.11h_s~(0.69). The correlation differs depending on the region. For Arctic ridges a linear relationship was found to be the best fit (h_k = 3.84h_s), while for the Subarctic ridges a power relationship (h_k=6.14h_s~(0.53)) best fit the data. The ratio of maximum keel to maximum sail is 5.17 on average (based on 308 values), and has also been calculated for each region mentioned above. Arctic ridges generally have a lower keel-to-sail ratio than those in Subarctic regions. The statistical distribution of keel-to-sail ratios is best represented by a gamma distribution. The average sail and keel widths were 12 and 36 m, respectively. The relationships between the sail and keel widths and other geometrical parameters were also determined. Variation of sail and keel thicknesses within individual ridges has been compared with the variability of all ridges. Ridge cross-sectional geometry can vary greatly along the length of a ridge, even over a short distance. A study was made on sail block thicknesses, and it was found that they correlate well with the sail height with a square root model. The typical macroporosity for a first-year ice ridge is 22% (based on 58 values) with an average sail macroporosity of 18% (based on 49 values) and average keel rubble macroporosity of 20% (based on 44 values). The average ridge consolidated layer thickness was 1.36 m based on 118 values. The variation of the consolidated layer was examined, and it was found that the layer tends to grow evenly with time over the width of the ridge cross section. A greater spacing between the measurements seemed to affect the variation, as it decreased with an increasing distance between each borehole. A statistical analysis based on 377 measurements of the consolidated layer of ridges in the Barents Sea showed that the gamma distribution well describes the distribution of the consolidated layer thicknesses in that area.