A lacustrine GDGT-temperature calibration from the Scandinavian Arctic to Antarctic: Renewed potential for the application of GDGT-paleothermometry in lakes Emma J. Pearson a,⇑ , Steve Juggins a , Helen M. Talbot b , Jan Weckstro ¨m c , Peter Rose ´n d , David B. Ryves e , Stephen J. Roberts f , Roland Schmidt g a School of Geography, Politics and Sociology, Newcastle University, Newcastle-upon-Tyne, NE1 7RU, UK b School of Civil Engineering and Geosciences, Newcastle University, Newcastle-upon-Tyne, NE1 7RU, UK c Department of Environmental Sciences, P.O. Box 65, University of Helsinki, Finland d Department of Ecology and Environmental Science, Umea ˚ University, SE-901 87 Umea ˚ , Sweden e Centre for Hydrological and Ecosystem Science, Department of Geography, Loughborough University, Loughborough LE11 3TU, UK f British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK g Institute of Limnology, Austrian Academy of Sciences, Mondsee, Austria Received 25 March 2011; accepted in revised form 26 July 2011; available online 2 August 2011 Abstract Quantitative climate reconstructions are fundamental to understand long-term trends in natural climate variability and to test climate models used to predict future climate change. Recent advances in molecular geochemistry have led to calibrations using glycerol dialkyl glycerol tetraethers (GDGTs), a group of temperature-sensitive membrane lipids found in Archaea and bacteria. GDGTs have been used to construct temperature indices for oceans (TEX 86 index) and soils (MBT/CBT index). The aim of this study is to examine GDGT-temperature relationships and assess the potential of constructing a GDGT-based pal- aeo-thermometer for lakes. We examine GDGT-temperature relationships using core top sediments from 90 lakes across a north–south transect from the Scandinavian Arctic to Antarctica including sites from Finland, Sweden, Siberia, the UK, Aus- tria, Turkey, Ethiopia, Uganda, Chile, South Georgia and the Antarctic Peninsula. We examine a suite of 15 GDGTs, includ- ing compounds used in the TEX 86 and MBT/CBT indices and reflecting the broad range of GDGT inputs to small lake systems. GDGTs are present in varying proportions in all lakes examined. The TEX 86 index is not applicable to our sites because of the large relative proportions of soil derived and methanogenic components. Similarly, the MBT/CBT index is also not appli- cable and predicts temperatures considerably lower than those measured. We examine relationships between individual GDGT compounds and temperature, pH, conductivity and water depth. Temperature accounts for a large and statistically independent fraction of variation in branched GDGT composition. We propose a GDGT-temperature regression model with high accuracy and precision (R 2 = 0.88; RMSE = 2.0 °C; RMSEP = 2.1 °C) for use in lakes based on a subset of branched GDGT compounds and highlight the potential of this new method for reconstructing past temperatures using lake sediments. Ó 2011 Elsevier Ltd. All rights reserved. 1. INTRODUCTION Lake sediments are useful archives of past environmen- tal and climate change. However, to date there is no robust method for directly reconstructing past temperatures using lake sediments since most methods rely on biological 0016-7037/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.gca.2011.07.042 ⇑ Corresponding author. Tel.: + 44 0 191 222 6757; fax: +44 0 191 222 5421. E-mail address: emma.pearson@ncl.ac.uk (E.J. Pearson). www.elsevier.com/locate/gca Available online at www.sciencedirect.com Geochimica et Cosmochimica Acta 75 (2011) 6225–6238