Ground truthing molecular proxies through archaeal physiology

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Membrane lipids form the cellular envelope, and are preserved on million to billion-year timescales. Although lipids do not contain the same depth of taxonomic information as nucleic acids, their isotopic composition provides insight into a microbe’s lifestyle, including carbon source and fixation pathway. In specific cases, lipids can be developed into molecular proxies by parameterizing the organism’s response to environmental changes, such as temperature. Molecular proxies require a detailed understanding of the lipid lifecycle, from the physiology of the source organism(s) to preservation in marine sediments. My PhD work focused on understanding the integrated effects of archaeal physiology on a molecular proxy for ocean temperature known as TEX86. My more recent work explores the use of archaeal lipids as a record of the isotopic composition of dissolved inorganic carbon. Intriguingly, at low CO2 levels archaeal lipids may hold promise as a pCO2 paleobarometer, similar to the alkenone paleobarometer.