Seven Decades of Coastal Change at Barter Island, Alaska: Exploring the Importance of Waves and Temperature on Erosion of Coastal Permafrost Bluffs

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.

Shoreline change rates and land to sea sediment and soil organic carbon transfer in eastern Parry Peninsula from 1965 to 2020 (Amundsen Gulf, Canada)

“…The general orientation of the coast, the duration of the sea ice-season, the ground ice content, wave power and local climate has been identified as driving factors of erosion on Arctic coasts (Gibbs et al, 2021;Irrgang et al, 2022). In eastern Parry Peninsula, the sediment remobilization seems to be slow due to the limited wave action.…”

“…Indeed, changes occurring on those ice-rich unconsolidated coasts are governed by permafrost thawing and wave impact, resulting in rapid mass movements, such as thaw slumps or block failures. The wave power on ice-rich unconsolidated coast of the Beaufort Sea (Tuktoyaktuk, Yukon coast, Mackenzie Delta) is more significant due to their orientation and exposure to a larger fetch area (Manson et al, 2005;Berry et al, 2021;Gibbs et al, 2021). The groundice content of those coasts is also much higher and coastal retreat can exceed 20 m/yr in some areas or massive groundice (Lantuit & Pollar, 2008;Obu et al, 2017;Lim et al, 2020;Berry et al, 2021).…”

Measuring and Attributing Sedimentary and Geomorphic Responses to Modern Climate Change: Challenges and Opportunities

“…Sediment‐sampling programs have decreased substantially since the 1980s due to limited resources, such that recent changes in fluvial sedimentary systems cannot be quantified reliably (Warrick & Milliman, 2018). For some geomorphic processes high‐resolution time series are not required; it is possible to calculate rates of glacier or coastal retreat using measurements from photographs taken decades apart (e.g., Gibbs et al., 2021). But in contrast, when we want to quantify rates, patterns, and nuances of climatic on fluvial or wind‐driven sediment transport, often the necessary data just do not exist.…”

Assessing Drivers of Coastal Tundra Retreat at Point Hope, Alaska

“…However, factors controlling tundra retreat may differ from site to site, with a detailed analysis at Barter Island, Alaska by Gibbs et al. (2021) indicating that annual scale variability in incident wave power is a predominant factor in bluff retreat.…”

“…Land-based topographic measurements or air or space-based lidar can similarly be used to quantify contour or volumetric changes. Tools such as the Digital Shoreline Analysis System (DSAS; e.g., Himmelstoss et al, 2018) have previously been used to estimate decadal and longer shoreline change rates for much of the US Arctic coastline from various shoreline data products; these analyses collectively indicate that coastal land losses in the region are generally widespread but exhibit considerable alongshore variability (e.g., Gibbs et al, 2019Gibbs et al, , 2021. However, only a select number of studies have focused on event scale evolution of beach, bluff, and tundra systems.…”