The role and relevance of rising air temperatures to bluff erosion in Arctic Alaska

Ferdinand J Oberle, Li H Erikson, Ann Gibbs, Bruce M Richmond and Thomas D Lorenson, USGS Pacific Coastal and Marine Science Center, Santa Cruz, CA, United States
Along the Arctic coast of Alaska, bluff erosion is widespread, may be accelerating, and is threatening defense and energy-related infrastructure, coastal habitats, and Native communities. Along the U.S. Beaufort Sea coast, long-term bluff recession rates average ~2.5m/yr since the 1950s, but with highspatial variability. Recent frequent measurements of the north facing bluffs at Barter Island (BTI), located near the U.S./Canadian border, indicate accelerating rates of erosion. These unconsolidated permafrost bluffs (average ~ 8 m height), with variable but often high ice-content, are susceptible to both mechanical and thermal erosion. The dominant processes that contribute to the apparent rise in erosion rates are spatial and temporal changes in sea ice, wave exposure, and increasing sea and air temperatures. In this study we employ wave and storm surge models and a suite of field measurements using Unmanned Aerial System (UAS) based thermal imaging techniques, thermistor arrays, and high-resolution imagery of BTI to characterize the dominant forcing parameters and evaluate the relative contribution of each to mechanical erosion and thermo-denudation.

Results indicate that while both cumulative wave energy flux and air temperatures have increased over the past decade, the high air temperature anomalies in October of every year since 2010 and of the 2019 summer season have triggered several thermal denudation events that occurred in 2019. Monthly mean temperature anomalies during these times ranged from 1°C to 4°C for a base period of 1980 -2009. The high air temperature anomalies are reflected in the heat conductivity maps of the BTI bluff face which showed ~5°C warmer bluff faces in September 2019 compared to previous years (2017). These measurements, supplemented with penetrating ground temperature arrays, are being used to test and develop a heat transfer model for use in a permafrost thermo-abrasion and denudation bluff erosion model.