Variability of coastal change along the western Yukon Coast

Because the Yukon coast along the Beaufort Sea has the highest ground ice contents in the Canadian Arctic and, in addition, faces the direction of most effective storms, this section of coast is considered to be highly vulnerable to the effects of climate change. In order to gain insight into the regional coastal dynamics, a quantification of coastal change was undertaken that allowed the determination of spatial and temporal variability of coastal change along a 35 km long section of coast, stretching from Komakuk to the international border. Shorelines from several years between 1951 and 2009 were digitized from georeferenced aerial photographs and an ortho-rectified SPOT image. Shoreline change statistics were subsequently calculated using the Digital Shoreline Analysis System (DSAS) extension for Esri ArcGIS. Theodolite and real-time kinematic GPS data that was collected during several surveys between 1991 and 2012 at two Geological Survey of Canada (GSC) monitoring sites (Border site and Komakuk site) were analysed to provide higher temporal resolution of coastal change for the last two decades. Additionally, the field survey data enabled an assessment to be made of the contribution of geomorphic variables (i.e. beach slope, beach width, cliff slope, absolute cliff height, relative cliff height) towards explaining changes of coastal erosion. According to the findings, the mean annual erosion along the western Yukon coast has been -1.2 ± 0.4 m/a over the entire period of study, with the rates decreasing through time from -1.4 ± 0.6 m/a between 1951 and 1972, to -1.2 ± 0.5 m/a between 1972 and 2009. However, site specific investigations show that there are differences in the mean erosion rates and in temporal trends. To the west at the Border site, the mean annual erosion rate is -1.3 ± 0.3 m/a, and the rates have recently accelerated, while at Komakuk in the east of the study area, the mean annual erosion rate is -0.9 ± 0.2 m/a, with the rates decelerating over time. A comparison of these findings to erosion rates from the Alaskan Beaufort Sea coast indicates that there is a general spatial pattern of decreasing erosion rates from the west to the east. The quantified erosion rates also enabled the calculation of mean annual land loss between 1951 and 2009, which amounted to 4.5 ha/a. An analysis of the influence of shore profile parameters on mean annual erosion rates showed a statistically significant correlation between beach widths and erosion rates (r=0.84) at the Border site. There is also a strong but insignificant correlation between absolute cliff heights and erosion rates at the Border, but no correlations of shore profile parameters with erosion could be distinguished for the Komakuk site

Variability of Arctic coastal erosion along the western Yukon coast

Arctic coastal erosion can have substantial impacts on coastal infrastructure, sometimes prompting the need for aggressive adaptation strategies. It can also induce the release of large quantities of organic carbon and nutrients directly into the nearshore with potential impacts on the ecosystem and/or transformation into greenhouse gases upon contact with sea water. The recent major changes in summer sea ice extent, as well as the warming of sea temperature could potentially lead to greater erosion rates and amplify these processes, yet few studies have quantified erosion in the Canadian Arctic over the period including the 2007 and 2012 minima in sea ice. In this study, we present erosion rates for the western Yukon coast, a 35 km long stretch between the Komakuk Beach Distant Early Warning Line station in the east and the Canada-USA border in the west. Shoreline position data from 44 aerial photographs as well as a SPOT image were analyzed to determine rates spanning 58 years (1951-2009). These remote sensing data were analyzed with the Digital Shoreline Analysis System (DSAS) extension for ESRI ArcGIS. Additionally, total station and real time kinematic global positioning system survey data from coastal monitoring sites maintained by the Geological Survey of Canada at Komakuk Beach and at the border were used to compute rates for the time period between 1991 and 2012. These two datasets together with LiDAR (Light Detection And Ranging) data collected in 2012 and 2013 allowed us to measure shoreline evolution and total volumetric land loss over the past 61 years. Mean annual volumetric land loss for the whole coastal stretch between 1951 and 2009 was calculated to be 250,000 m3/a. DSAS results show rates of coastal erosion in the region have not changed significantly over time. A comparison of the mean annual erosion from 1951 to 1972 to the time period of 1972 to 2009 shows a slight deceleration from 1.4 m/a to 1.2 m/a. A clearer trend towards decreasing erosion was distinguished at the Komakuk Beach study site, where mean annual erosion decelerated from 1.92 m/a to 0.49 m/a during the time from 1951 to 2009. By contrast, coastal erosion at the Canada-USA border increased during the same time period from 1.3 m/a to 1.8 m/a. Work is under way to better understand these local differences and the overall nature of erosion along the Yukon coast