Improving the brGDGT Paleotemperature Proxy: New Insights from High-Latitude Lake Sediments

Abstract:

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are an important tool for reconstructing paleotemperatures from lake sediments. Currently, most studies use a calibration developed from East African lake sediments (Russell et al., 2018, Organic Geochemistry). While this data set spans a wide and geologically relevant range of temperatures, the low seasonality associated with its lakes means that they may not be directly comparable to sites at higher latitudes. This is especially true for its cold end-members, which experience fundamentally different conditions than most cold lakes due to a lack of ice cover. Indeed, research suggested early on that brGDGT-derived temperatures in high latitude regions were biased towards the summer. However, detailed studies have since shown that brGDGT production in lakes is not limited to summer months. In addition, analytical advances have separated previously convoluted brGDGT isomers that have distinct correlations with environmental variables. These developments motivate the re-examination of the brGDGT temperature proxy in cold regions. Here, we add surface sediments from 43 lakes across Baffin Island (Nunavut), northern Quebec, and Iceland to existing data sets and use a combination of temperature loggers and meteorological stations to examine the effects of seasonality on brGDGT-derived temperatures. In addition, we develop modified brGDGT indices that not only improve calibrations against air temperature and lake water pH, but also enhance our understanding of the relationships between these compounds and environmental variables.