ALBERT

Description: Subsea permafrost forms when sea level rise from deglaciation or coastal erosion results in inundation of terrestrial permafrost. The response of permafrost to flooding in these settings will be determined by both ice-rich Pleistocene deposits and the thermokarst basins that thawed out during the Holocene. Thermokarst processes lower ground ice content, create partially drained and refrozen depressions (Alases) and thaw bulbs (taliks) beneath them, warm the ground, and can thaw the ground below sea level. We hypothesize that inundated Alases offshore with relatively lower ice content and higher porewater salinities in their sediments (possibly resulting from lagoon interaction) thaw faster than Yedoma terrain. To test this hypothesis, we estimated permafrost thaw rates offshore of the Bykovsky Peninsula in Tiksi Bay, northeastern Siberia using geoelectric surveys with floating electrodes. The surveys traversed a former undrained lagoon, drained and refrozen Alas deposits, and undisturbed Yedoma terrain at varying distances from shore. A continuous Yedoma-Alas-beach-lagoon survey was also carried out to obtain an indication of pre-inundation subsurface electrical resistivity. While the estimated degradation rates of the submerged Yedoma lies in the range of similar sites, and slows with increasing distance offshore, the Alas rates were more diverse and at least twice as fast within 125 m of the coastline. The latter is possibly due to saline lagoon water that infiltrated the Alas while it was still unfrozen. The ice-bearing permafrost depths of the former lagoon were generally the deepest of the terrain units, but displayed poor correlation with distance offshore. We attribute this to heterogeneous talik thickness upon the lagoon to sea transition, as well as permafrost aggradation processes beneath the spit. Given the prevalence of thermokarst basins and lakes along parts of the Arctic coastline, their effect on subsea permafrost degradation must be similarly prevalent. Remote sensing analyses suggest that 40% of lagoons wider than 500 m originated in thermokarst basins along the pan-Arctic coast. The more rapid degradation rates shown here suggest that low-ice content conduits for fluid flow may be more common than currently thought based on thermal modelling of subsea permafrost distribution.

Description: As air temperatures rise and sea ice cover declines in the Arctic, permafrost coastal cliffs thaw more rapidly and wave energy rises. Thus, as the open water season continues to lengthen, climate change triggers a large part of the Arctic shoreline to become increasingly vulnerable to erosion. Arctic erosion supplies nutrient-laden and carbon-rich sediment into nearshore ecosystems. A retreating coastline also has consequences for residential, cultural, and industrial infrastructure. Despite its importance, erosion is currently neglected in global climate models, and existing physics-based numerical models of Arctic shoreline erosion are too complex and regionally-focused to be applied on a pan-Arctic scale. Here, we apply our simplified numerical erosion model, ArcticBeach v1.0, to the entire Arctic coastline. ArcticBeach v1.0 has previously been shown to simulate retreat rates at two sites that differ substantially in their main mechanisms of retreat (sub-aerial erosion/thaw slumping versus notch/block erosion). The model uses heat and sediment volume balances in order to predict horizontal cliff retreat and vertical erosion of a fronting beach. It contains an erosion module that uses empirical equations to estimate cross-shore sediment transport, coupled to a storm surge module forced by wind. We present Arctic maps of regional variation in trends in 2-meter air temperature, sea ice concentration, and wind speed.