TEMPERATURE VARIABILITY FROM ARCTIC LAKE EL’GYGYTGYN (FAR EAST RUSSIA) DURING THE MID-PLEISTOCENE TRANSITION BASED ON BRGDGTS

The ability to reconstruct past temperatures using organic proxies is critical to our understanding of Arctic climate changes during the glacially active Pleistocene period. These proxies can be found in and analyzed from lake sediment cores allowing us to measure temperature changes across individual glacial-interglacial cycles as well as overall trends towards modern times. Our knowledge of Arctic continental climate spanning beyond ~100,000 years ago, the interval captured by Greenland ice core records, has been restricted by the lack of long and continuous sedimentary records due to large swaths of the northern hemisphere being periodically covered by ice sheets. In this study, we analyze bacterial membrane lipids (branched glycerol dialkyl glycerol tetraethers; (brGDGTs) contained in a sediment drill core from Lake El’gygytgyn in eastern Siberia. This lake bordering the Arctic Circle has remained unglaciated providing us with a unique 3.6 million-year record of sedimentary and biological activity. Using liquid chromatography and previously developed brGDGT-based temperature calibrations, we reconstructed arctic temperatures from the Mid-Pleistocene Transition (MPT) when glacial-interglacial cycles shifted from dominant periodicity of 41,000 to 100,000-years. This shift has been associated with a global cooling trend and with thicker, longer-lasting ice sheets. At Lake El’gygytgyn we find a clear pattern of alternating warming and cooling trends consistent with interglacial-glacial climate cycles, particularly during MIS 21 and 22 from 800 ka-900 ka. Our temperature record also exhibits a trend of overall cooling during glacial periods that is seen in other paleoclimate records such as the benthic oxygen isotope stack. Our brGDGT temperature record provides us with the opportunity to examine how biological proxies have historically responded to local and global climate change and provides new insights into how continental arctic climate changed during the MPT.