Modeling erosion of ice-rich permafrost bluffs along the Alaskan Beaufort Sea coast

The Arctic climate is changing, inducing accelerating retreat of ice-rich permafrost coastal
bluffs. Along Alaska’s Beaufort Sea coast, erosion rates have increased roughly threefold from 6.8 to
19 m yr⁻¹ since 1955 while the sea ice-free season has increased roughly twofold from 45 to 100 days since
1979. We develop a numerical model of bluff retreat to assess the relative roles of the length of sea ice-free
season, sea level, water temperature, nearshore wavefield, and permafrost temperature in controlling
erosion rates in this setting. The model captures the processes of erosion observed in short-term
monitoring experiments along the Beaufort Sea coast, including evolution of melt notches, topple of ice
wedge-bounded blocks, and degradation of these blocks. Model results agree with time-lapse imagery
of bluff evolution and time series of ocean-based instrumentation. Erosion is highly episodic with 40% of
erosion is accomplished during less than 5% of the sea ice-free season. Among the formulations of the
submarine erosion rate we assessed, we advocate those that employ both water temperature and nearshore
wavefield. As high water levels are a prerequisite for erosion, any future changes that increase the frequency
with which water levels exceed the base of the bluffs will increase rates of coastal erosion. The certain
increases in sea level and potential changes in storminess will both contribute to this effect. As water
temperature also influences erosion rates, any further expansion of the sea ice-free season into the
midsummer period of greatest insolation is likely to result in an additional increase in coastal retreat rates.