Temporal and spatial dynamics of Arctic coastal changes and the resulting impacts: Yukon Territory, Canada

anna.irrgang [ at ] awi.de


In the Arctic, temperatures are rising twice as fast as the global mean. Since most of the terrestrial Arctic is underlain by permafrost it is particularly vulnerable to rising air temperatures. Permafrost holds vast amounts of carbon which upon release can considerably impact the Earth climate system. Studying processes which lead to permafrost degradation and carbon mobilization is thus important for quantifying this impact. The erosion of permafrost coasts is one of these processes and results in the mobilization of previously frozen carbon from the cliff, as well as from the hinterland. Since 34% of the World’s coasts are characterized by the presence of permafrost, the net effect is substantial and leads to the release of large amounts of organic matter. Yet, little data on rates of shoreline change and fluxes of organic matter are available for the Arctic. This thesis fills a gap by providing new baseline data on the temporal and spatial variability of shoreline changes along the ice-rich Yukon coast in the western Canadian Arctic, as well as on subsequent impacts on the natural and human environment. Shoreline change rates were obtained from geocoded aerial images from the 1950s, 1970s and 1990s, as well as from satellite images from 2011. Differential global positioning system (DGPS) measurements of shore zone and cliff profiles along seven field sites were analyzed. Based on this data, shoreline changes were estimated for several time periods. Even though acceleration in shoreline retreat was not reflected in the mean shoreline change rates for the whole coast, analyses along six shorter sections of the coast revealed that coastal erosion is accelerating since the mid-1990s. DGPS field site measurements also indicate a rapid acceleration in shoreline retreat since 2006. Based on the shoreline change rates, sediment and soil organic carbon (SOC) fluxes to the Beaufort Sea were quantified. The SOC fluxes were calculated accounting for ground ice, which reduced the total flux rates by 19%. Sampling of the entire cliff, instead of just the upper meter, allowed the inclusion of SOC fluxes from the whole soil column, which increased the total SOC flux rate by 46%. Annually, 35.0×106 kg of SOC are mobilized by shoreline retreat from the Yukon coast, which is 131 kg SOC per metre of coast. These new estimations of SOC fluxes are nearly three times as high as the fluxes which were previously used for the region in organic carbon budgets. Retrogressive thaw slumps (RTSs) are a thermokarst landform, which occurs frequently along the Yukon coast. Analyses of geocoded aerial images from the 1950s and 1970s and satellite images from 2011 revealed that even though RTSs occur only along 28 km of the 238 km long shoreline, they occupy an area of 402 ha and deliver large amounts of sediment and carbon from the hinterland. For a better understanding of the initiation and activity of RTSs, univariate regression tree models were fed with 16 environmental variables, including shoreline change rates. Ground ice characteristics (volume and thickness) and terrain characteristics (terrain height and slope) appeared to be the most influencing factors for RTS initiation and activity. However, coastal erosion is considered to play a crucial role in setting the preconditions for RTS initiation and activity by removing the insulating layer from the massive ice body and eroding the outflow materials. The currently observed enhanced RTS activity along the Yukon coast is therefore considered to be linked to intensified coastal erosion processes. This thesis also investigated present and potential future impacts of coastal dynamics on manmade structures and cultural heritage along the Yukon coast. A cultural features database was created and the positions of these features were analyzed with respect to two projected shoreline positions for the year 2100. The analyses reveal that more than 50% of all known cultural features will be lost to the ocean due to coastal erosion by 2100. Further, the usage of the two only landings strips located along the coast will be very restricted. Travelling along the traditional boating routes is expected to become more challenging due to increasing sediment supply and dynamics. This thesis contributes to an enhanced understanding of past, present and potential future coastal changes and the resulting impacts on the natural and human environment along the Yukon coast. It shows that coastal changes are occurring at an accelerating pace and lead to impacts much greater than previously thought both in terms of net impact on the ecosystem and on infrastructure and cultural heritage.

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Irrgang, A. (2018): Temporal and spatial dynamics of Arctic coastal changes and the resulting impacts: Yukon Territory, Canada , PhD thesis, University of Potsdam.

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