SEARCHING FOR THE MID-BRUNHES EVENT IN THE TERRESTRIAL ARCTIC: AN ORGANIC GEOCHEMICAL PALEOCLIMATE RECORD FROM LAKE EL’GYGYTGYN, RUSSIA

The characteristic glacial and interglacial cycles of the Pleistocene underwent a subtle climatic transition at ~430 ka known as the Mid- Brunhes Event (MBE). Studies have noted that after this transition, the amplitude of the climatic cycles increased. Despite the indication of an MBE signal in many globally distributed paleoclimate records, the geographic extent and mechanism behind the climatic transition remain unclear. While the MBE is expressed in a number of southern hemisphere records its presence in northern hemisphere and terrestrial records is debated. Lake El’gygytgyn is located in the far- east Russian Arctic and provides the longest and most continuous record of Arctic climate, spanning the past 3.6 Ma. This study examines organic biomarkers in Lake El’gygytgyn sediments from 0- 800 ka at a resolution of ~1.5 ka to determine if the MBE is expressed in the terrestrial Arctic. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are utilized to reconstruct temperature variability and plant leaf wax n-alkanes are used to examine vegetation and hydrologic changes throughout the study interval. Statistical analysis of this, and other existing proxy data, indicates that a signal of the MBE is preserved in the Lake El’gygytgyn sediment record. BrGDGT temperature reconstructions indicate the terrestrial Arctic experienced both the warmest interglacial periods and coldest glacial periods after the MBE climatic transition. Arid glacial intervals and wetter interglacials are suggested by changes in the average chain length of n- alkanes, with wetter conditions predominating after the MBE.