Nearshore Carbon and Sediment Dynamics of an Eroding Permafrost Coast: Herschel Island, Yukon Territory, Canada

• Main Authors: Radosavljevic, Boris, Lantuit, Hugues, Fritz, Michael
• Format: Conference Object
• Language: unknown
• Published: 2012
• Subjects: Arctic; Yukon; Canada; Herschel Island; Van Veen; Climate change; Herschel; Ice; Ice Sheet; permafrost; Sea ice; Thermokarst
• Online Access: https://epic.awi.de/id/eprint/31943/; https://epic.awi.de/id/eprint/31943/1/2012_Boris_Radosavljevic_ArcticNet_small.pdf; https://hdl.handle.net/10013/epic.40644; https://hdl.handle.net/10013/epic.40644.d001

The study presented herein seeks to determine the fate of sediment and carbon supplied into the nearshore zone by coastal erosion and thermokarst in permafrost landscapes. To accomplish this, the sediment and carbon sources and sinks will be identified and quantified using remotely sensed imagery, bathymetric and sidescan surveys, shallow seismic profiles, and the interpretation of sediment cores. Coastal dynamics on arctic coasts are characterized by a seasonal dichotomy. Sea ice and landfast ice limit the length of the open-water season, armoring the coast against wave-induced erosion; while in the absence of ice the coast is susceptible to the combined effects of mechanical and thermal erosion processes. This results in high erosion rates along coasts characterized by ice-rich permafrost, like the western Canadian Arctic. Current estimates show that there is about twice as much carbon stored in permafrost as compared to the atmosphere. Of special interest is the potential climate feedback triggered by carbon release into the nearshore zone by coastal erosion, in a region that according to many climate change models will experience disproportionate warming. Herschel Island, the focus of the current study, is a push-moraine that formed at the northwestern limit of the Laurentide Ice Sheet. This part of the Canadian Yukon coast is characterized by high cliffs and numerous retrogressive thaw slumps, indicating the presence of large massive ice bodies susceptible to permafrost degradation. This study aims to elucidate the erosion, transport, and deposition dynamics of sediments and carbon that enter the nearshore zone. We focus on the marine realm, directly accompanying studies that aim at quantifying and characterizing the terrestrial aspects of coastal erosion in the area. A combination of methods is used to identify sediment sources, their characteristics, pathways, and sinks. An interferometric sidescan sonar system is used in conjunction with Van-Veen grab-samples to create bathymetric and sidescan mosaics that allow for an areal view of sediment pathways, sources, and possible sinks. Surface sediments are analyzed for grain-size, nutrients, and carbon content. Using time series data acquired over multiple field seasons and satellite imagery will enable ascertaining the importance of cliff- vs. thaw slump erosion in supplying sediments. Sedimentation rates are obtained from sediment cores using 137Cs, 210Pb, and 14C dating methods. Simultaneous analyses of the carbon content in the cores provide the necessary data for a regional sediment and carbon budget. A seismic sub bottom profiler is used to gain insights into the depositional history and submarine permafrost evolution of the region.