Development of new global lake brGDGT-temperature calibrations: advances, applications and challenges
Authors: Pearson Emma , Juggins Steve , Roberts Stephen , Phillips Tony , Hodgson Dominic , Naafs David , Foster Louise , Allbrook Harry 
Published: February 2023

Quantitative paleoclimate reconstructions are fundamental to understand long-term trends in natural climate variability and to test climate models used to predict future climate change. Branched glycerol dialkyl glycerol tetrathers (brGDGTs) are bacterial cell membrane lipids, with a molecular structure that strongly depends on growth temperature, and global and regional lacustrine brGDGT-temperature calibrations have been used to reconstruct past temperatures using lake sediments from a range of environments.Application of the global and regional Antarctic and sub-Antarctic brGDGT calibrations (Pearson et al., 2011; Foster et al., 2016) however, suggests a need to expand and improve reconstruction accuracy for cold, extreme environments (Roberts et al., 2017). We construct new global lacustrine brGDGT-temperature calibrations using datasets obtained via brGDGT analysis using two existing (single and dual column LCMS) analytical methods, and comprising Antarctic and sub-Antarctic samples, and other available published datasets.Advancements in calibration studies principally comprise two main routes: one via expansion of calibration datasets, the other by improving reconstructions. We address both of these by both expanding existing datasets, and also by evaluating a range of different statistical approaches, all of which are subjected to rigorous cross-validation. For each of our calibration datasets we investigate a range of different statistical modelling approaches to predict mean annual temperature, mean summer temperature and mean temperature of months above freezing, where available, derived from field measurements and the gridded ERA5 dataset (Hersbach et al., 2019) across the whole and <15&#176;C subset of the temperature range.We apply our new calibrations to existing published lake sediment core records from contrasting environments to compare and evaluate the performance of the different analytical and statistical methods. Our findings highlight some of the complexities and caveats of the different methods and have important implications for the application of lacustrine brGDGT temperature calibrations to lakes at a global scale.&#160;ReferencesFoster LC, Pearson EJ, Juggins S, Hodgson DA, Saunders KM, Verleyen E, Roberts SJ.&#160;Development of a regional glycerol dialkyl glycerol tetraether (GDGT)&#8211;temperature calibration for Antarctic and sub-Antarctic lakes.&#160;Earth and Planetary Science Letters&#160;2016,&#160;433, 370-379.Hersbach, H., Bell, B., Berrisford, P., Biavati, G., Hor&#225;nyi, A., Mu&#241;oz Sabater, J., Nicolas, J., Peubey, C., Radu, R., Rozum, I., Schepers, D., Simmons, A., Soci, C., Dee, D., Th&#233;paut, J-N. (2019): ERA5 monthly averaged data on single levels from 1979 to present. Copernicus Climate Change Service (C3S) Climate Data Store (CDS). (Accessed on 08-Sep-2020, 29-Mar-2021), 10.24381/cds.f17050d7Pearson EJ, Juggins S, Talbot HM, Weckstr&#246;m J, Ros&#233;n P, Ryves D, Roberts S, Schmidt R.&#160;A lacustrine GDGT-temperature calibration from the Scandinavian Arctic to Antarctic: Renewed potential for the application of GDGT-paleothermometry in lakes.&#160;Geochimica et Cosmochimica Acta&#160;2011,&#160;75(20), 6225-6238.Roberts SJ, Monien P, Foster LC, Loftfield J, Hocking EP, Schnetger B, Pearson EJ, Juggins S, Fretwell P, Ireland L, Ochyra R, Haworth AR, Allen CS, Moreton SG, Davies SJ, Brumsack H-J, Bentley MJ, Hodgson DA.&#160;Past penguin colony responses to explosive volcanism on the Antarctic Peninsula.&#160;Nature Communications&#160;2017,&#160;8, 14914.