Abstracts

The Yukon Coast in Canada is anice-rich permafrost coast and highly sensitive to changingenvironmental conditions. Retrogressive thaw slumps are a commonthermoerosion feature along this coast, and develop through thethawing of exposed ice-rich permafrost on slopes and removal ofaccumulating debris. They contribute large amounts of sediment,including organic carbon and nitrogen, to the nearshore zone. The objective of this study was to 1) identify the climatic andgeomorphological drivers of sediment-meltwater release, 2) quantifythe amount of released meltwater, sediment, organic carbon andnitrogen, and 3) project the evolution of sediment-meltwaterrelease of retrogressive thaw slumps in a changing future climate. The analysis is based on data collected over 18 days in July 2013and 18 days in August 2012. A cut-throat flume was set up in themain sediment-meltwater channel of the largest retrogressive thawslump on Herschel Island. In addition, two weather stations, one ontop of the undisturbed tundra and one on the slump floor, measuredincoming solar radiation, air temperature, wind speed andprecipitation. The discharge volume eroding from the ice-richpermafrost and retreating snowbanks was measured and compared tothe meteorological data collected in real time with a resolution ofone minute. The results show that the release ofsediment-meltwater from thawing of the ice-rich permafrost headwallis strongly related to snowmelt, incoming solar radiation and airtemperature. Snowmelt led to seasonal differences, especially dueto the additional contribution of water to the erodingsediment-meltwater from headwall ablation, lead to dilution of thesediment-meltwater composition. Incoming solar radiation and airtemperature were the main drivers for diurnal and inter-diurnalfluctuations. In July (2013), the retrogressive thaw slump releasedabout 25 000 m of sediment-meltwater, containing 225 kg dissolvedorganic carbon and 2050 t of sediment, which in turn included 33 torganic carbon, and 4 t total nitrogen. In August (2012), just 15600 m of sediment-meltwater was released, since there was noadditional contribution from snowmelt. However, even without theadditional dilution, 281 kg dissolved organic carbon was released.The sediment concentration was twice as high as in July, withsediment contents of up to 457 g l-1 and 3058 t of sediment,including 53 t organic carbon and 5 t nitrogen, being released. In addition, the data from the 36 days of observations from Slump Dwere upscaled to cover the main summer season of 1 July to 31August (62 days) and to include all 229 active retrogressive thawslumps along the Yukon Coast. In total, all retrogressive thawslumps along the Yukon Coast contribute a minimum of 1.4 Mio. msediment-meltwater each thawing season, containing a minimum of 172000 t sediment with 3119 t organic carbon, 327 t nitrogen and 17 tdissolved organic carbon. Therefore, in addition to the coastalerosion input to the Beaufort Sea, retrogressive thaw slumpsadditionallyAdvisors/Committee Members: Lantuit, Hugues (advisor).