Pablo Martinez Sosa, Jess Tierney, Ioana Cristina Stefanescu , Emily Dearing Crampton-Flood, Bryan N Shuman, Cody Routson

Despite widespread use of branched glycerol dialkyl glycerol tetraethers (brGDGTs) for paleo-temperature reconstruction, no global calibration for their application in lakes has been generated since improved analytical methods have allowed for the separation of the structural isomers. This is a substantial obstacle for the application of this tool as soil calibrations underestimate temperature values when applied to lake sediments. Here, we present a comprehensive dataset (N = 261) of lacustrine brGDGT distributions spanning a wide range of geographical locations, environmental temperatures, and lakewater pH values. Empirical Orthogonal Function (EOF) analysis on the fractional abundance of brGDGTS indicates that temperature exerts a strong control (explaining 86% of the variance) on the lipid distribution. However, the influence of water chemistry is less clear, as pH and conductivity have a weak influence on brGDGT distributions. We use our dataset to generate a new Bayesian temperature calibration, which has an R²= 0.85 and RMSE = 2.8°C. Application of this new calibration to a previously published lake core record demonstrates that it generates values comparable with instrumental observations. Our new calibration facilitates the use of lacustrine brGDGTs to reconstruct continental temperatures, a vital piece of information for understanding past climates.