Novel hydrological and carbon cycle constraints from the isotopic composition of archaeal lipid biomarkers
Funded through the Emmy Noether Program of the Deutsche Forschungsgemeinschaft (DFG)
Reliable reconstructions of past climate depend on the accurate assessment of major parameters of the Earth’s climate system such as temperature, atmospheric CO2 concentrations (pCO2), and the variability of the hydrological cycle. Organic chemical fossils preserved in sediments, so-called lipid biomarkers, have played significant roles as indicators (so-called proxies) for these parameters. A distinct subgroup of biomarkers produced by archaea, isoprenoid ether lipids called GDGTs, is ubiquitous in aquatic sediments deposited over the last ~200 million years. While archaeal GDGTs are now widely studied as paleotemperature proxies, the isotopic systematics of archaeal GDGTs remain largely unexplored.
Our preliminary studies suggest great potential for the H and C isotopic composition of archaeal lipids to provide novel insights into past changes of the global hydrological and carbon cycles. We postulate that the hydrogen isotopic composition of a specific GDGT called crenarchaeol (Delta 2HCren) is primarily dependent on Delta 2H of ambient water of the archaeal habitat, suggesting a potential for Delta 2HCren to serve as a tracer for hydrological changes. Further, our work suggests that the carbon isotopic composition of crenarchaeol (Delta 13CCren) is dependent on ambient pCO2 of the surface ocean and may thus hold promise as a novel tool to reconstruct past atmospheric pCO2 levels (as both are directly connected in key ocean regions). We propose to verify the applicability of these novel proxies in both laboratory experiments (using archaeal cultures) and in the modern environment (using water column and surficial sediment samples). We then use these proxies to address long-standing and novel topics in Paleogene-Neogene paleoclimate research. Specifically, we will investigate the coupling of temperature and hydroclimate during the Quaternary as well as the relationship between temperature and pCO2, and thus climate sensitivity, during the late Paleogene and early Neogene.