High-Resolution Biomarker Proxy Records of Arctic Climate Change During the Mid-Pleistocene Transition from Lake El’gygytgyn (Far East Russia)

Abstract:

The ability to reconstruct past temperatures is critical to our understanding of Arctic climate during the glacially active Pleistocene epoch and can be used to infer future consequences of modern climate change. Our knowledge of Arctic continental climate spanning beyond ~100,000 years ago, the interval captured by Greenland ice core records, is restricted by the lack of long and continuous sedimentary records due to the erosive overlap of repeated glaciations. Here, we analyze distributions of branched glycerol dialkyl glycerol tetraethers (brGDGTs) within a sediment drill core from Lake El’gygytgyn in eastern Siberia to reconstruct paleotemperatures for the region. This lake bordering the Arctic Circle remained unglaciated providing us with a unique 3.6 million-year record of sedimentary and biological activity. Using the MBT’_5Me proxy, we reconstruct arctic temperatures at 2,000-year resolution during the Mid-Pleistocene Transition (MPT) when glacial-interglacial cycles shifted from a dominant periodicity of 41,000 to 100,000-years and global atmospheric CO₂ levels decreased. We also examine ratios of plant leaf wax n-alkanes to understand changes in the local vegetation community during these climatic shifts. At Lake El’gygytgyn, we find that the terrestrial temperature record of the MPT does not show persistent glacial-period cooling prior to the temperature minimum during Marine Isotope Stage (MIS) 22. Rather, we observe a relatively weak MIS 25 and sub-orbital temperature variations that characterize MIS 22-24, suggesting variable climate modes may have been an important component of the MPT. Pollen and leaf wax-inferred vegetation changes corroborate these patterns and further document a pronounced and persistent warming at the onset of MIS 21. Our brGDGT temperature record provides us with the opportunity to examine for the first time 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.