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 to Holocene 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, δ13Corg) and stable water isotopes (δ18O, δD, d excess) 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 (22 800±280 cal. a BP, Unit A), which has vertically subsided in places due to subsequent development of a deep thermokarst lake that initiated around 11 800 cal. a BP (Unit B). At about 9000 cal. 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 1060 cal. a BP, including post-drainage sediment freezing from the top down to 154 cm 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 11 800 cal. 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 thermokarst-affected regions of the Arctic.
Bibliographical noteFunding Information:
Fieldwork was supported by NSF (ARC-0732735), NASA (NNX08AJ37G) and the US National Park Service. Additional funding was provided by the German Federal Ministry of Education and Research (BMBF Grant No. 01DJ14003), the Western Alaska Landscape Conservation Cooperative Project (WA2011-02), RFBR (#16-040045-a) and the ERC (#338335). J. Lenz was supported by a Christiane N?sslein-Volhard-Foundation grant, a dissertation stipend from the University of Potsdam, and the Helmholtz Graduate School for Polar and Marine Research (POLMAR), and acknowledges an invitation by S. Mischke to the Faculty of Earth Sciences (University of Iceland) for a research visit to finalize this study. We thank K. Walter Anthony and L. Farquharson for field support and discussions, and A. Myrbo and L. Farquharson for assisting with core splitting, imaging and GEOTEK scanning at the LacCore facility at the University of Minnesota. Further, we would like to thank H. Kemnitz, I. Sch?pan, S. Wulf and O. Appelt (GFZ) for facilitating SEM imaging as well as geochemical analyses of tephra. We thank L. Farquharson, S. Lauterbach and one anonymous reviewer for providing helpful comments that improved the manuscript. Any use of trade, product or firm names is for descriptive purposes only and does not imply endorsement by the US Government.
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