Permafrost carbon degradation and transport pathways at thermokarst coasts in the Arctic

• Main Authors: Tanski, George, Ruttor, Saskia, Lantuit, Hugues, Knoblauch, Christian, Radosavljevic, Boris, Ramage, Justine, Mollenhauer, Gesine, Strauss, Jens, Fritz, Michael
• Format: Conference Object
• Language: unknown
• Published: 2016
• Subjects: Arctic; Climate change; Herschel; Herschel Island; Ice; permafrost; Thermokarst; Tundra; Yukon
• Online Access: https://epic.awi.de/id/eprint/41251/; https://epic.awi.de/id/eprint/41251/1/GTanski_Talk_ICOP.pdf; https://hdl.handle.net/10013/epic.48176; https://hdl.handle.net/10013/epic.48176.d001

Climate change has a strong impact on permafrost coasts in the Arctic. With increasing air and water temperatures, ice-rich permafrost coasts will thaw, which will lead to enhanced thermokarst and erosion. Upon erosion, large amounts of organic carbon previously stored for thousands of years are remobilized and either emitted as greenhouse gases to the atmosphere, redeposited within the landward nearshore zone, or released into the ocean. Yet, little is known about carbon degradation before the organic matter enters the nearshore zone of the ocean. The objective of this study was to investigate these processes at ice-rich thermokarst coasts, by focusing on retrogressive thaw slumps. The study aimed at determining the quantity of organic carbon and nitrogen in undisturbed and non-disturbed (thermokarst affected) coastal stretches, to detect its degradation and accumulation pattern after thawing, as well as its fate in the nearshore of the ocean. A retrogressive thaw slump located on Herschel Island (Yukon Territory, Canada) was sampled systematically along transects from the undisturbed parts (tundra, permafrost headwall) to disturbed parts (mudpool and slump floor) and the nearshore zone (marine sediments). These thermokarst landforms are ideal study sites as they spatially expose different transport and accumulation stages of thawed permafrost sediments before entering the ocean. Total and dissolved organic carbon (TOC and DOC) as well as total and dissolved nitrogen (TN and DN) were analyzed to quantify carbon and nitrogen loss. C/N-ratios, stable carbon isotope concentrations (δ13C-TOC and δ13C-DOC), nutrient concentrations (ammonium, nitrite, nitrate), and lipid biomarkers were analyzed to estimate degradation, carbon metabolization, as well as nitrification and plant assimilation processes. Furthermore, dating of lead isotopes (Pb-210) in nearshore sediments and conductivity-temperature-depth (CTD) profiles of the sea water in front of the slump were analyzed to assess the possible fate of the organic ...