Abstract
Observational data of coastal change over much of the Arctic are limited largely due to its immensity, remoteness, harsh environment, and restricted periods of sunlight and ice-free conditions. Barter Island, Alaska, is one of the few locations where an extensive, observational dataset exists, which enables a detailed assessment of the trends and patterns of coastal change over decadal to annual time scales. Coastal bluff and shoreline positions were delineated from maps, aerial photographs, and satellite imagery acquired between 1947 and 2020, and at a nearly annual rate since 2004. Rates and patterns of shoreline and bluff change varied widely over the observational period. Shorelines showed a consistent trend of southerly erosion and westerly extension of the western termini of Barter Island and Bernard Spit, which has accelerated since at least 2000. The 3.2 km long stretch of ocean-exposed coastal permafrost bluffs retreated on average 114 m and at a maximum of 163 m at an average long-term rate (70 year) of 1.6 ± 0.1 m/yr. The long-term retreat rate was punctuated by individual years with retreat rates up to four times higher (6.6 ± 1.9 m/yr; 2012–2013) and both long-term (multidecadal) and short-term (annual to semiannual) rates showed a steady increase in retreat rates through time, with consistently high rates since 2015. A best-fit polynomial trend indicated acceleration in retreat rates that was independent of the large spatial and temporal variations observed on an annual basis. Rates and patterns of bluff retreat were correlated to incident wave energy and air and water temperatures. Wave energy was found to be the dominant driver of bluff retreat, followed by sea surface temperatures and warming air temperatures that are considered proxies for evaluating thermo-erosion and denudation. Normalized anomalies of cumulative wave energy, duration of open water, and air and sea temperature showed at least three distinct phases since 1979: a negative phase prior to 1987, a mixed phase between 1987 and the early to late 2000s, followed by a positive phase extending to 2020. The duration of the open-water season has tripled since 1979, increasing from approximately 40 to 140 days. Acceleration in retreat rates at Barter Island may be related to increases in both thermodenudation, associated with increasing air temperature, and the number of niche-forming and block-collapsing episodes associated with higher air and water temperature, more frequent storms, and longer ice-free conditions in the Beaufort Sea.
Highlights
This article is an open access articleProcesses driving coastal change in permafrost environments can be fundamentally reduced to mechanical and thermal processes [1,2], and shorelines anchored by permafrostrich substrates and those influenced by the presence of sea ice, are highly vulnerable to the effects of climate change
The results indicate that inshore wave power has increased four-fold over the past decade compared to the long-term mean, and that the increase is continuing, commensurate with the increasing bluff retreat rates
The study is unique with respect to the high temporal resolution of the observational data as well as the detailed comparison of bluff change with wave power and sea surface temperatures as indicators of thermoabrasion and ambient air temperatures as proxies for thermodenudation
Summary
This article is an open access articleProcesses driving coastal change in permafrost environments can be fundamentally reduced to mechanical and thermal processes [1,2], and shorelines anchored by permafrostrich substrates and those influenced by the presence of sea ice, are highly vulnerable to the effects of climate change. 2021, 13, 4420 and direction and water levels in the Alaskan coastal region over the past several decades (e.g., [3,4,5,6,7]) will likely drive a related response in permafrost coastline behavior because of the linked mechanisms of shoreline change [8]. Attributing this response in coastal behavior is problematic, largely because observational data are limited due to the Arctic’s remoteness, harsh environment, poor geodetic infrastructure, and restricted windows of opportunity for observation (limited daylight and ice-free conditions). Shoreline change rates calculated using these data indicate the coast has dominantly erosional over the past seven decades; no clear statistically significant change in trend through time was identified based on the decadal-scale time periods [9]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call