An 8.6 million year reconstruction of paleotemperatures and paleovegetation from Lake Baikal, Russia, derived from Baikal Drilling Project core materials. This dataset also includes compiled paleovegetation data from the Late Pliocene and Early Pleistocene from boreal regions and a new global mean surface temperature stack derived from published sea surface temperature records. Paleotemperatures were estimated from the methylation of branched glycerol dialkyl glycerol tetraethers. Paleovegetation was reconstructed from plant wax n-alkane distributions and published pollen data. Paleovegetation data were compiled from published studies.

Methods:All sediments analyzed for biomarkers were freeze dried and weighed prior to homogenization. Lipids were extracted by an accelerated solvent extractor (ASE) 350 using 2:1 dichloromethane: methanol (c.f. Auderset et al., 2020; Powers et al., 2010). Oven temperature was set to 100°C, rinse volume to 150%, purge time to 120 seconds, heating time to 5 minutes, and with 4 10-minute static cycles. Total lipid extracts were spiked with 100 µL of a general recovery standard (20.5 ng/µL 5α-androstane, 20.5 ng/µL stearyl stearate, 20.5 ng/µL 1,1'-binapthyl, 20.5 ng/µL cis-11-eicosenoic acid, 20.5 ng/µL 19-methyleicosenoic acid, 20.5 ng/µL C20:1 Δ11-eicosenol, and 20.5 ng/µL 5α-androstan-3β-ol), desulfurized by sequential addition of activated copper wire, and evaporated under N2 prior to elution on a 0.5 g dry-packed LC-NH2 column to separate neutral (4 mL 2:1 dichloromethane: isopropanol), acid (4 mL 4% acetic acid in diethyl ether), and polar (4 mL methanol) fractions. Neutral and polar fractions were recombined and again dried under N2 prior to elution on a wet-packed silica gel (0.5 g, 60 Å, 70–230 mesh, Millipore) column with 3 mL hexanes (apolar / aliphatic), 4 mL dichloromethane (semi-polar / aromatic), and 4 mL methanol (polar / alcohols). To further isolate GDGTs, the polar/alcohols (methanol) fraction was further eluted over alumina oxide (0.85 g, J.T. Baker, 0537-01) by elution of 4 mL 9:1 hexane: dichloromethane, 4 mL 1:1 dichloromethane: methanol (containing GDGTs), and 4 mL 100% methanol. The 1:1 dichloromethane: methanol fraction was then dried over N2 and shipped to Brown University, where they were analyzed for GDGTs on an Agilent/Hewlett Packard 1100 series liquid chromatograph mass spectrometer (LC-MS) using two UHPLC columns (BEH HILIC columns, 2.1 x 150 mm, 1.7 μm, Waters) in series using the protocol of Hopmans et al. 2016. Prior to analysis, samples were passed through a 0.45 μm filter and spiked with a known quantity of a C46 glycerol trialkyl glycerol tetraether (GTGT) internal standard. Selective ion monitoring was used to measure m/z 1302, 1300, 1298, 1296, 1292, 1050, 1048, 1046, 1036, 1034, 1032, 1022, 1020, 1018, and 744. Peak areas were quantified manually. Concentrations of individual GDGT molecules are reported in nanograms per gram of sediment (ng/g sed) assuming a 1:1 relationship between the response factor of the C46 GTGT and the individual brGDGTs (Huguet et al, 2006). While this assumption may not capture the exact response factors of individual brGDGTs, it is sufficient for understanding the relative concentrations of different brGDGTs in this sample set. Further funding information: PR 1414/1-1 Deutsche Forchungsgemeinshaft Priority Program "ICDP" 1006 Geological Society of America Continental Drilling Science Division Graduate Student Grant 13282-21* Sigma Xi Grants in Aid of Research G20211001-101