Past landscape and permafrost dynamics in Arctic Alaska based on sedimentary records

• Main Authors: Lenz, Josefine, Grosse, Guido, Jones, Benjamin M., Fritz, Michael, Wetterich, Sebastian
• Format: Conference Object
• Language: unknown
• Published: 2015
• Subjects: Arctic; Climate change; Magnetic susceptibility; permafrost; Seward Peninsula; Thermokarst; Alaska
• Online Access: https://epic.awi.de/id/eprint/38007/; http://www.awi.de/en/research/research_divisions/geosciences/periglacial_research/events/past_gateways_conference_may_2015/; https://hdl.handle.net/10013/epic.45562

Permafrost-related processes are key ecosystem drivers in the Arctic system and often an indicator for long-term environmental change. Understanding past periods of permafrost degradation and aggradation is crucial to estimate future response of the terrestrial Arctic to climate change. We collected sediment cores from one thermokarst lake and two drained thermokarst lake basins from the northern Seward Peninsula and the Teshekpuk Lake region (Alaska) to gain insights into past landscape dynamics since the late Pleistocene in these continuous permafrost regions. We applied a multi-proxy approach on sediment cores using methods of micropaleontology (ostracods, rhizopods), sedimentology (grain size analyzes, magnetic susceptibility), biogeochemistry (TN, TC, TOC, δ13C), as well as geochronology (AMS radiocarbon dating, tephrochronology). The environmental evolution of the three study sites covers different temporal scales. Preliminary radiocarbon dating results of three short cores (core ID P_1, P_2 and P_3) from a thermokarst lake North of Teshekpuk Lake revealed mid- to late Holocene ages with numerous age reversals in spite of well layered lake sediments. A core-based study (core ID Kit-43) of thermokarst lake sediments on northern Seward Peninsula yielded a radiocarbon chronology in agreement with stratigraphic sequences; with its base dated to the Last Glacial Maximum at 22,800 cal a BP. The third core (core ID Kit-64) from a drained lake basin in the same study region was dated to the Early to Mid-Wisconsin and will be discussed in detail. As observed in aerial and satellite images, GG basin on the northern Seward Peninsula drained in Spring 2005 (Figure 1, Lenz et al., accepted). The core recovered in spring 2009 has preserved the permafrost re-aggradation after lake drainage with frozen sediment from the lake sediment surface down to a depth of 266 cm (Figure 2). Below 266 cm the unfrozen talik was still existent. The sedimentary record yielded prevailing terrestrial conditions prior to 45,000 a BP. Fine ...