Abstract
A regional network of quantitative reconstructions of past climate variability is required to test climate models. In recent studies, temperature calibration models based on the relative abundances of sedimentary glycerol dialkyl glycerol tetraethers (GDGTs) have enabled past temperature reconstructions in both marine and terrestrial environments. Nevertheless, to date these methods have not been widely applied in high latitude environments due to poor performance of the GDGT–temperature calibrations at lower temperatures. To address this we studied 32 lakes from Antarctica, the sub-Antarctic Islands and Southern Chile to: 1) quantify their GDGT composition and investigate the environmental controls on GDGT composition; and 2) develop a GDGT–temperature calibration model for inferring past temperatures from Antarctic and sub-Antarctic lakes. GDGTs were found in all 32 lakes studied and in 31 lakes branched GDGTs (brGDGTs) were the dominant compounds. Statistical analyses of brGDGT composition in relation to temperature, pH, conductivity and water depth showed that the composition of brGDGTs is strongly correlated with mean summer air temperature (MSAT). This enabled the development of the first regional brGDGT–temperature calibration for use in Antarctic and sub-Antarctic lakes using four brGDGT compounds (GDGT-Ib, GDGT-II, GDGT-III and GDGT-IIIb). A key discovery was that GDGT-IIIb is of particular importance in cold lacustrine environments. The addition of this compound significantly improved the model's performance from r2=0.67, RMSEP-LOO (leave-one-out)=2.23 °C, RMSEP-H (h-block)=2.37 °C when applying the re-calibrated global GDGT–temperature calibration to our Antarctic dataset to r2=0.83, RMSEP-LOO=1.68 °C, RMSEP-H=1.65 °C for our new Antarctic calibration. This shows that Antarctic and sub-Antarctic, and possibly other high latitude, palaeotemperature reconstructions should be based on a regional GDGT–temperature calibration where specific compounds can be identified and included to improve model performance. Finally, downcore temperature reconstructions using the new Antarctic brGDGT–temperature calibration were tested in sub-Antarctic Fan Lake from South Georgia providing a proof of concept for the new calibration model in the Southern Hemisphere.
Highlights
Previous studies of past climates in high-latitude regions have used a range of biological proxies including changes in accumulation rates and species composition of pollen, diatoms, pigments and chironomids to give indirect qualitative or quantitative inferences about past environmental changes (e.g., Anderson et al., 2001; Verleyen et al, 2003; Hodgson et al, 2005; Rolland et al, 2009; Watcham et al, 2011; Strother et al, 2015)
We found that glycerol dialkyl glycerol tetraethers (GDGTs) were present in all 32 Antarctic, subAntarctic and Southern Chilean lakes and that branched GDGTs (brGDGTs) were dominant in 31 of the lakes studied
Statistical tests showed that summer temperature was the primary environmental control on the composition of brGDGTs in Antarctic lakes, and that the effect of mean summer air temperature (MSAT) was largely independent of other limnological variables
Summary
Previous studies of past climates in high-latitude regions have used a range of biological proxies including changes in accumulation rates and species composition of pollen, diatoms, pigments and chironomids to give indirect qualitative or quantitative inferences about past environmental changes (e.g., Anderson et al., 2001; Verleyen et al, 2003; Hodgson et al, 2005; Rolland et al, 2009; Watcham et al, 2011; Strother et al, 2015). Substantial improvement in our understanding of past atmospheric temperature at low altitudes without the complicating factors of changing ocean currents (which limit the application of marinebased palaeothermometry through redistributing heat e.g., Kim et al, 2012) and high altitude temperature effects (which apply to most ice core reconstructions e.g., Mulvaney et al, 2012). One such approach is the application of glycerol dialkyl glycerol tetraethers (GDGTs). In these few sites the GDGT–temperature relationship does not appear to be as strong as the global relationship, suggesting a need to expand upon and further investigate the environmental controls on GDGT composition in Antarctic lakes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
