Monday, October 02, 2017, 12:00PM - 1:00PM
Dept. of Earth and Planetary Sciences, Harvard University
SEEC room S228 (Sievers room)
Understanding the sources of prokaryotic tetraether membrane lipids in the environment: Controls on glycerol-dialkyl-glycerol-tetraethers (GDGTs) in lacustrine and oceanic sediments and implications for paleoclimate reconstructions
Tetraether membrane lipids (GDGTs) of Bacteria and Archaea have become a powerful tool in paleoceanography and paleolimnology, providing records of past variations in mean ocean- and lake surface temperatures, as well as atmospheric air temperatures, in strata as old as the Cretaceous. The application of GDGT-based proxies is, however, often complicated in settings in which the sedimentary lipid pool is contributed by multiple allochthonous (terrigenous) and autochthonous (aquatic) sources, as this may potentially confound the link between GDGT composition and climatic signals. In this seminar we will explore the diverse biological sources of branched (i.e., bacterial) and isoprenoidal (i.e., archaeal) GDGTs in freshwater lakes, using unpublished stable isotope- and molecular biological data from the water column of meromictic Lake Lugano (Switzerland), as well as a collection of lake sediments from the Alps. Recent culturing experiments further revealed that the archaeal GDGTs found in marine sediments may not as quantitatively reflect sea surface temperatures as previously assumed. Besides phylogenetic differences between archaeal populations, several temperature-independent factors have been proposed that influence the marine GDGT-based temperature proxy TEX86, including growth stage, nutrient concentration, oxygen saturation, and contribution from benthic and/or deep water archaea. Here we will further discuss the potential of compound specific stable isotope analysis for disentangling GDGT sources in oceanic settings.
Free and open to the public.