Branched glycerol dialkyl glycerol tetraethers (brGDGTs) from lake sediments in Alaska, Yukon, and Northwest Territories

The brGDGTs used in this study derive from the shallow sediments of 43 lakes in Alaska, Yukon, and Northwest Territories across a latitudinal gradient of 59.5 to 69.4 °N and elevations of 2 to 1187 masl in July 2019. The top 5-10 cm of lake sediment was collected from ~30 cm water depth and stored in Whirlpack bags. The samples were kept at -20 °C at camp and then shipped to the University of Toronto, Mississauga. BrGDGTs were ultimately obtained from 6 grams of sediment following successive purification via column chromatography. The purified samples were analyzed for brGDGT abundance via ultra-high-performance liquid chromatography - mass spectrometry using an Agilent Technologies 1290 Series II UHPLC coupled to an AB Sciex 4500Q triple quadrupole mass spectrometer at the University of Toronto, Mississauga. The resultant brGDGT distributions are presented as relative abundances, which were then used to calculate a variety of common indices (MBT’5me, CBT’, and IR6me). To assess climate sensitivity, monthly temperatures and precipitation amounts from 1991- 2020 were modified from the ERA5 reanalysis data from Copernicus Climate Changer Service information. The brGDGT distributions display a warm-season temperature bias, which agrees with previous studies. Mean temperatures of months above freezing (MAF) best correlate with the relative abundance of the IIIa brGDGT, which is unique to this region. MAF also displays an expectedly high correlation with the MBT’5me. As such, lake-derived brGDGT distributions from Alaska, Yukon, and Northwest Territories offer an opportunity to reconstruct past warm-season temperatures in this region.