Widescale rates of coastal change on ice-rich permafrost coastlines under specific landfast ice exposure settings, across the Northwest Canadian Arctic

Abstract

The Arctic is experiencing some of the most rapid environmental changes on Earth, yet the interactions among landfast ice, permafrost cliffs, and retrogressive thaw slumps have remained understudied, due to their remote and challenging geographic conditions. Advancements in satellite technology, offering enhanced spatial and temporal resolution with free accessibility, now enable remote monitoring of these dynamic coastlines. An innovative method to detect variations in landfast ice coverage and open-water seasons as a coastal exposure control is introduced. Analysis of the southern Beaufort Sea region in the Northwest Canadian Arctic demonstrates an average increase of ≈20 days in open-water season duration since the early 21st century, with notable spatial variability. Although the Arctic Coastal Database (ACD) has provided historical rates of coastal change, these are now outdated and reliant on questionable extrapolation methodologies. This research addresses key limitations in the ACD by increasing spatial resolution from 200 m to 10 m, thereby capturing critical transition zones and large retrogressive thaw slumps previously undetected in coarser analyses. Furthermore, this research highlights the inadequacy of shoreline metrics for representing volumetric changes in permafrost cliffs and slumps, which are better suited for dynamic features such as spits. A semi-automated approach has been developed to classify permafrost coastal geomorphology using a satellite derived base to height ratio, which effectively identifies spits, cliffs, and retrogressive thaw slumps. A volume based correction factor was trained and applied using heli-surveying across the outer islands to refine erosion rates for permafrost cliffs >2 m in height to better represent material outflow, however a correction factor is not yet applicable for retrogressive thaw slumps. Findings reveal that cliffs dominate the geomorphology of the southern Beaufort Sea coastline (53%), followed by spits and inundated tundra (39%), and retrogressive thaw slumps (8%). An updated average regional erosion rate of 4.49 m3m-2yr-1 has been established for the ≈860 km ice-rich coastline, which is 3.5 times higher than the ACD’s estimate. Future research should prioritize volumetric data for retrogressive thaw slumps to enhance correction factors and facilitate the development of interannual pan-Arctic erosion rates. Such advancements are critical for accurately predicting material outflow and supporting future climate modelling efforts.

Date of Award	22 May 2025
Original language	English
Awarding Institution	Northumbria University
Supervisor	Michael Lim (Supervisor) & Paul Mann (Supervisor)