Examining the Mid- Brunhes Event in the Terrestrial Arctic: an Organic Geochemical Record from Lake El’gygytgyn, Russia

Abstract:

The characteristic glacial and interglacial cycles of the Pleistocene underwent a climatic transition at ~430 ka known as the Mid- Brunhes Event (MBE). Numerous 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 of the climatic transition remains unknown. 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, most continuous record of Arctic climate (3.6 Ma). This study examines organic biomarkers in the Lake El’gygytgyn sediment core to determine if the MBE is expressed in the terrestrial Arctic. The paleoclimate reconstruction spans the interval of 0- 730 ka at a resolution of ~1.5 ka. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are utilized to reconstruct temperature variability and plant leaf wax n-alkanes are used to examine vegetation 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 recorded by changes in the average chain length of n- alkanes, with wetter interglacials predominating after the MBE. Possibly, changes in Antarctic bottom water production and associated variability in North Pacific upwelling are responsible for transmitting the MBE signal from the southern hemisphere to Lake El’gygytgyn.