The seaward landfast ice edge (SLIE) is simple to define conceptually but more difficult to determine in practice, partly since both the location and a lack of motion must be determined over time, implying that a single observation is insufficient. The authors examine different definitions of landfast ice used by others and then propose the authors own, consisting of two criteria: 1) the ice is contiguous with the land, and 2) the ice lacks detectable motion for approximately 20 days. This definition is applied to a time series of Radarsat synthetic aperture radar (SAR) imagery of the northern Alaska coast. Analysis reveals the presence of nodes where the SLIE exists more frequently. Nodes occur near the 20m isobath, suggesting grounding helps stabilize the SLIE in these locations. Comparison with studies from the 1970’s suggests that the stable extent of landfast sea ice has changed very little. Further work will carried out to determine whether there has been any change in the annual cycle. The authors also note that any comparisons must take into account relevant definitions and methods. This is particularly so with operational datasets that lack the benefit of hindsight such as the National Ice Center Ice Charts, which can differ significantly from the authors own for the same time period.

Landfast sea ice is a seasonal phenomena in the Alaskan Arctic and throughout its annual existence, between formation in late fall and break-up in late spring, it is shaped by a range of thermodynamic and dynamic forces. The results of a manual and an automated technique to derive positions of the seaward landfast ice edge (SLIE) as it changes over time from synthetic aperture radar (SAR) data covering the Alaskan Arctic coast and nearshore waters from east of Point Lay, Alaska to the Mackenzie delta. Observing the variability in the position of the SLIE for a large study area over the course of the year identifies the occurrences of significant change including the timing of freeze-up and break-up and episodic events in between. It is also possible to identify the maximum stable extent of the landfast ice for a given period, which should prove valuable for all nearshore activity in the Arctic. We can give a greater understanding of the factors controlling the SLIE position by calculating the standard deviation in landfast ice width along the coast. This analysis identifies stable nodes along the SLIE where variability is small and processes, as of yet unidentified, helps to stabilize the landfast ice edge.