Past Permafrost and Landscape Dynamics in Central Beringia: Two Case Studies from Drained Thermokarst Lake Basin Cores

• Main Authors: Lenz, Josefine, Wetterich, Sebastian, Jones, Benjamin M., Walter Anthony, Katey M., Meyer, Hanno, Bobrov, Anatoly, Wulf, Sabine, Grosse, Guido
• Format: Conference Object
• Language: unknown
• Published: 2016
• Subjects: Arctic; Ice; Magnetic susceptibility; permafrost; Seward Peninsula; Thermokarst; Beringia
• Online Access: https://epic.awi.de/id/eprint/41258/; https://epic.awi.de/id/eprint/41258/1/Poster_ICOP2016_Lenz.pdf; https://www.conftool.pro/icop2016/index.php?page=browseSessions&form_session=144; https://hdl.handle.net/10013/epic.48175; https://hdl.handle.net/10013/epic.48175.d001

Thermokarst is a commonly observed process in the Arctic and an indicator of permafrost degradation. The formation of thermokarst landforms may indicate a localized disturbance to the ground thermal regime or be indicative of widespread permafrost degradation driven by climate-induced top-down permafrost thaw. Thermokarst lakes are one of the most prominent landforms that develop in ice-rich arctic and boreal lowlands. In our study, we investigate two drained thermokarst lake basins on the northern Seward Peninsula in Central Beringia to gain insights into site-specific landscape development and past permafrost dynamics during glacial and interglacial periods. A 350 cm permafrost core (core ID: Kit-43) and a 400 cm permafrost core (core ID: Kit-64) were acquired from two drained lake basins that represent contrasting geological settings and cover a range of time periods (Mid-Wisconsin to Holocene). Kit-64 was a first generation lake in yedoma upland; Kit-43 was a later generation lake in a thermokarst-shaped lowland. The cores were analyzed using a multi-proxy approach including sedimentological (magnetic susceptibility, grain size), biogeochemical (TN, TC, TOC, δ13C), and micropaleontological methods (ostracods, testaceans), tephra analyses, radiocarbon dating on sediments, as well as isotope geochemical methods (δD and δ18O) on intra-sedimentary ground ice. The Kit-64 core was acquired from a first generation lake basin on a yedoma upland that preserved a depositional environment of more than 45,000 years (Lenz et al., 2015) including: (1) Mid-Wisconsin yedoma accumulation, (2) intermediate wetland development between 41,500 and 44,500 yr BP, (3) South Killeak Maar tephra deposition that interrupted the wetland development, (4) continued terrestrial yedoma accumulation probably until the Late Glacial when a significant gap in the sedimentary record indicates formation of thermokarst lakes in the surroundings of this site that prevented further accumulation, and (5) finally a 300 cal yr BP thermokarst lake ...