Understanding Thermokarst Lake Dynamics in Arctic Alaska: Case Studies based on Sediment Cores

• Main Authors: Lenz, Josefine, Wetterich, Sebastian, Jones, Benjamin M., Grosse, Guido
• Format: Conference Object
• Language: unknown
• Published: 2015
• Subjects: Arctic; Ice; Magnetic susceptibility; permafrost; Seward Peninsula; Thermokarst; Alaska; Siberia
• Online Access: https://epic.awi.de/id/eprint/38004/; https://epic.awi.de/id/eprint/38004/1/Poster_ASSW_2015_Lenz_et_al.pdf; http://www.assw2015.org/program/index.html; https://hdl.handle.net/10013/epic.45555; https://hdl.handle.net/10013/epic.45555.d001

Arctic landscape dynamics are an indicator of long-term natural processes. Within the Arctic system, permafrost-related processes are key ecosystem drivers and influence regional landscape evolution, hydrology, etc. Thermokarst lake dynamics, involving initiation, expansion, drainage, and re-initiation, have reshaped vast Arctic lowlands in Siberia, Alaska, and Canada since the last deglaciation (~15,000 years ago). Today, thermokarst lakes across the circum-Arctic are responding quite variably to a warming. A multitude of remote sensing studies reports on losses in thermokarst lake area due to increased evapotranspiration and drying or rapid lake drainage, while increased thermokarst lake formation is reported from more northern regions. To understand these modern dynamics and place observations into a long-term context it is necessary to understand the paleodynamics of thermokarst lakes. A useful technique to achieve this is the use of core-based reconstructions of paleoenvironmental conditions during the lake history using various sedimentological, biogeochemical, and biological proxies. We applied a multi-proxy approach on sediment cores making use of methods in sedimentology (grain size analyses, magnetic susceptibility), biogeochemistry (TN, TC, TOC, δ13C), geochronology (14C, tephra chronology), and micropaleontology (ostracods, rhizopods). Our studies on modern but also recently drained basins in Arctic Alaska (USA) are based on sediment cores from the northern Seward Peninsula and the Teshekpuk Lake region and provide insights into past landscape dynamics since the late Pleistocene in these continuous permafrost regions. GG basin on the northern Seward Peninsula, shown in the figure below, drained in spring 2005. Its lake initiation was radiocarbon-dated to about 300 years before present (BP) and was indicated by freshwater ostracods (e.g. Fabaeformiscandina protzi) and hydrophilic rhizopods (e.g. Cyclopyxis kahli). Before this, ice-rich silty and organic-rich sediments known as yedoma deposits ...