PALEOTEMPERATURE RECONSTRUCTIONS FROM LAKE EL’GYGYTGYN (FAR EAST RUSSIA) BASED ON BRANCHED GDGTS

Drill coring at Lake El’gygytgyn (NE Russia) in 2009 recovered sediments spanning the past 3.6 Ma from the largest and oldest unglaciated Arctic lake basin. These sediments provide the first terrestrial Arctic paleoclimate record spanning the Plio-Pleistocene and thus offer a unique opportunity for examining high-latitude climate variability beyond the relatively short 100 Ka interval captured by Greenland ice core records. Here, we use an organic geochemical paleothermometer, the Methylation of Branched Tetraethers/Cyclization of Branched Tetraethers (MBT/CBT) Index (Weijers et al., 2007), to reconstruct temperature at Lake El’gygytgyn. The MBT/CBT paleothermometer is based on branched glycerol dialkyl glycerol tetraethers (GDGTs) and provides a proxy for mean annual soil temperature, which is often similar to mean annual air temperature. Branched GDGTs were originally identified in soils and peat but subsequent research has shown that branched GDGTs are also produced in-situ in lakes. Thus, a number of different calibrations between MBT/CBT ratios in lake surface sediments and lake surface temperature have been suggested. We find that branched GDGTs are abundant in Lake El’gygytgyn sediments and that relative changes in the MBT/CBT-derived temperature record are in agreement with the overall patterns of glacial-interglacial climate variability noted in global climate records. At present, MBT/CBT cannot be used to reconstruct absolute temperature at Lake El’gygytgyn due to the lack of a site specific calibration; however, this study demonstrates that relative temperature changes derived from the MBT/CBT Index at Lake El’gygytgyn are robust. Overall, application of the MBT/CBT paleothermometer to Lake El’gygytgyn sediments appears to be a promising technique for generating a Plio-Pleistocene temperature record from the western Arctic. If a site specific MBT/CBT calibration can be created, then the potential exists for creating a 3.6 Ma record of Arctic continental temperature variability.