Evidence of multiple thermokarst lake generations from an 11800-year-old permafrost core on the northern Seward Peninsula, Alaska

• Published in: Boreas
• Main Authors: Lenz, Josefine, Wetterich, Sebastian, Jones, Benjamin M., Meyer, Hanno, Bobrov, Anatoly, Grosse, Guido
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Institut für Geowissenschaften; Arctic; Talik; Ice; Magnetic susceptibility; permafrost; Seward Peninsula; Thermokarst; Alaska; Beringia
• Online Access: https://publishup.uni-potsdam.de/opus4-ubp/frontdoor/index/index/docId/44902; https://doi.org/10.1111/bor.12186

Permafrost degradation influences the morphology, biogeochemical cycling and hydrology of Arctic landscapes over a range of time scales. To reconstruct temporal patterns of early to late Holocene permafrost and thermokarst dynamics, site-specific palaeo-records are needed. Here we present a multi-proxy study of a 350-cm-long permafrost core from a drained lake basin on the northern Seward Peninsula, Alaska, revealing Lateglacial toHolocene thermokarst lake dynamics in a central location of Beringia. Use of radiocarbon dating, micropalaeontology (ostracods and testaceans), sedimentology (grain-size analyses, magnetic susceptibility, tephra analyses), geochemistry (total nitrogen and carbon, total organic carbon, C-13(org)) and stable water isotopes (O-18, D, dexcess) of ground ice allowed the reconstruction of several distinct thermokarst lake phases. These include a pre-lacustrine environment at the base of the core characterized by the Devil Mountain Maar tephra (22800 +/- 280cal. a BP, Unit A), which has vertically subsided in places due to subsequent development of a deep thermokarst lake that initiated around 11800cal. a BP (Unit B). At about 9000cal. a BP this lake transitioned from a stable depositional environment to a very dynamic lake system (Unit C) characterized by fluctuating lake levels, potentially intermediate wetland development, and expansion and erosion of shore deposits. Complete drainage of this lake occurred at 1060cal. a BP, including post-drainage sediment freezing from the top down to 154cm and gradual accumulation of terrestrial peat (Unit D), as well as uniform upward talik refreezing. This core-based reconstruction of multiple thermokarst lake generations since 11800cal. a BP improves our understanding of the temporal scales of thermokarst lake development from initiation to drainage, demonstrates complex landscape evolution in the ice-rich permafrost regions of Central Beringia during the Lateglacial and Holocene, and enhances our understanding of biogeochemical cycles in ...