Further Improvements to Understandings of Extreme Arctic Sea Ice Thickness Derived From Upward Looking Sonar Ice Data

摘要

Long-term observations of extreme draft sea ice features have been identified from upward looking sonar (ULS) datasets spanning several years in various Arctic regions including the Canadian Beaufort Sea, offshore of Northeast Greenland and the Chukchi Sea. The quantification of the distribution of magnitude and frequency of occurrence of very deep ice keels is important to the design and strategic deployment plans for offshore platforms and shipping and navigation in these ice covered waters. An earlier analysis (Amundrud, 2004) led to an empirically determined relationship between the maximum ice draft and the draft of nearby level ice based on draft observations from the Beaufort Sea in the 1990s. It was argued that ridging in first-year ice continues as long as the force required to drive an ice block over the ridge is less than the force at which the level ice next to the ridge will buckle. An empirical upper limit was developed for the maximum sea ice thickness resulting from deformation processes based on the relationship of maximum ice thickness as a function of nearby values of undeformed ice thickness. Using the more extensive ULS ice keel data sets now available in the Beaufort Sea as well as the NE Greenland and Chukchi Sea areas, these methods were re-evaluated and updated. The results are compared among the regions in terms of the potential source areas for very large ridging activity. The implication of the maximum ice drafts derived in this empirical approach for sea ice ridging are discussed in the context of other ice types that may be present including multi-year ice and floating glacial ice (icebergs and ice islands).