Refinement of the Branched GDGT Paleoenvironmental Proxy through Complementary Analytical Approaches

Abstract

Molecular fossils, known as biomarkers, are useful tools that allow us to make robust inferences about past climate through the geological record. Among these, glycerol dialkyl glycerol tetraethers (GDGTs) stand out as presenting sensitivity to environmental changes while being globally abundant in environments ranging from marine sediments to soils. The two main types of GDGTs, branched and isoprenoid, are generally considered to be sensitive to environmental parameters in specific settings. In marine sediments isoGDGTs respond to water temperature, while in terrestrial environments brGDGTs respond to temperature and pH. While the response of GDGTs to the environment has been empirically demonstrated, some uncertainties remain on the mechanism through which they capture the environment. This is particularly notable for brGDGTs, for which the source organisms are only partially understood. A better understanding on the production of these molecules can help us better understand the Earth's Climate System. The objective of this dissertation is to clarify and quantify the influence that environmental parameters have on the distribution of brGDGTs, particularly in freshwater environments. The results from this are then applied to a larger scale as the basis to generate a global brGDGT calibration for lakes. Finally, the unique response and distribution of all GDGTs observed in the previous chapter is used to generate a classification algorithm for both marine and terrestrial environments in the geological record. We hope that this work generates a better understanding of the biology and ecology of the GDGT source organisms, and how we can use this knowledge to reconstruct past environments.