The Role of Thermal Denudation in Erosion of Ice-Rich Permafrost Coasts in an Enclosed Bay (Gulf of Kruzenstern, Western Yamal, Russia)

Abstract

Coastal erosion in the Arctic has numerous internal and external environmental drivers. Internal drivers include sediment composition, permafrost properties and exposure which contribute to its spatial variability, while changing hydrometeorological conditions act as external drivers and determine the temporal evolution of shoreline retreat. To reveal the relative role of these factors, we investigated patterns of coastal dynamics in an enclosed bay in the southwestern Kara Sea, Russia, namely the Gulf of Kruzenstern, which is protected from open-sea waves by the Sharapovy Koshki Islands. Using multitemporal satellite imagery, we calculated decadal-scale retreat rates for erosional segments of the coastal plain from 1964 to 2019. In the field, we studied and described Quaternary sediments and massive ground-ice beds outcropping in the coastal bluffs. Using data from regional hydrometeorological stations and climate reanalysis (ERA), we estimated changes in the air thawing index, sea ice-free period duration, wind-wave energy and total hydrometeorological stress for the Gulf of Kruzenstern, and compared it to Kharasavey and Marre-Sale open-sea segments north and south of the gulf to understand how the hydrometeorological forcing changes in an enclosed bay. The calculated average shoreline retreat rates along the Gulf in 1964–2010 were 0.5 ± 0.2 m yr−1; the highest erosion of up to 1.7 ± 0.2 m yr−1 was typical for segments containing outcrops of massive ground-ice beds and facing to the northwest. These retreat rates, driven by intensive thermal denudation, are comparable to long-term rates measured along open-sea sites known from literature. As a result of recent air temperature and sea ice-free period increases, average erosion rates rose to 0.9 ± 0.7 m yr−1 in 2010–2019, with extremes of up to 2.4 ± 0.7 m yr−1. The increased mean decadal-scale erosion rates were also associated with higher spatial variability in erosion patterns. Analysis of the air thawing index, wave energy potential and their total effect showed that inside the Gulf of Kruzenstern, 85% of coastal erosion is attributable to thermal denudation associated with the air thawing index, if we suppose that at open-sea locations, the input of wave energy and air thawing index is equal. Our findings highlight the importance of permafrost degradation and thermal denudation on increases in ice-rich permafrost bluff erosion in the Arctic.

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

“…Similar to permafrost bluffs elsewhere in the Arctic, primary bluff failure modes are a combination of thermal denudation on the bluff face throughout the summer and thermomechanical removal of debris material fronting the bluffs and niching of the base associated with waves and high-water levels (wind or storm surge) followed by rotational slumping and block collapse [1,2,[28][29][30][31]. Ground ice typically occupies 60-90% of the volume of near-surface deposits [16,32], and it is a major factor contributing to the high coastal erosion rates [33].…”

Projected increase of Arctic coastal erosion and its sensitivity to warming in the 21st Century

“…2a), as the sediment transport from ocean waves play a secondary role in coastal retreat in such formations. Erosion is also predominantly thermally driven in enclosed bays and in coastal segments protected by spits and barrier islands, where the fetch for ocean waves is limited [39], although barrier island themselves are often susceptible to wave abrasion [40]. In contrast, erosion of ice-rich cliffs, which occur extensively along the Beaufort and Laptev Sea coast for example [6][7][8], requires the mechanical action from ocean waves to open notches at the land-sea interface, causing the subsequent failure of often still frozen large blocks of permafrost.…”

Snow Patches and Their Influence on Coastal Erosion at Baydaratskaya Bay Coast, Kara Sea, Russian Arctic

“…The coasts of the western Russian Arctic are composed of permafrost unconsolidated saline sediments [29,30]. Their retreat is associated with thermal degradation of soils during a period with positive air temperatures; the thermodenudation process [31][32][33][34][35]. For different key-sites coasts of the Kara Sea, long-term (30-50 years) average annual retreat rates range from 0.3 to 2 m/year [36][37][38][39][40].…”