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Mahoney, A.R., 2006

Alaska landfast sea ice dynamics

Bibliographic Reference

Mahoney, A.R., 2006, Alaska landfast sea ice dynamics: University of Alaska Fairbanks, Ph.D. dissertation, 135 p.


This thesis describes a comprehensive, multi-scale study of landfast sea ice along the northern Alaska coast combining ice-, land- and space-based observations. In order to analyze regional-scale spatio-temporal variability, we apply a rigorous definition of landfast ice to Radarsat Synthetic Aperture Radar (SAR) imagery of Alaska's northern coast. In doing so, we delineate the seaward landfast ice edge (SLIE) approximately every 10 days during the 8 annual cycles between 1996 and 2004. Our results show that bathymetry influences the landfast ice throughout its development and that the 20 m isobath is a good approximation of the SLIE in mid- to late winter. Comparison with work from the 1970s indicates that landfast ice has formed later and broken-up earlier in recent years. On an interannual basis, we find that the timing of landfast ice formation correlates with the incursion of pack ice into coastal waters, suggesting that northward summertime retreat of the perennial sea ice edge might be contributing to later formation of landfast ice. In spring, break-up correlates well with the onset of thawing temperatures. A multi-decadal trend towards earlier spring thawing suggests that our observation of earlier break-up may be part of a long-term pattern. To observe local-scale landfast ice dynamics, a land-based marine radar was used near Barrow, Alaska between 2003 and 2005. Of particular interest were detachment events, which represent a significant hazard to hunters, scientists and others who work upon landfast sea ice. Local meteorological conditions showed little relationship with observed detachments and estimated water stresses were insufficient to overcome anchoring strengths, estimated from field measurements of grounded ridges. Therefore, we conclude additional decoupling processes, such as sea level surges or erosion of keels, must occur in addition to current stress to detach the landfast ice. These processes, whatever they may be, are thought to be the cause of oscillations in signal strength (flickering) observed in radar targets. This flickering can be seen up to several hours prior to detachment and holds promise of being a useful predictive tool.* *This dissertation is a compound document (contains both a paper copy and a DVD as part of the dissertation). The DVD requires the following system requirements: Adobe Acrobat; Microsoft Office; QuickTime; Internet browser.

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