ORGANIC CHEMISTRY FOR PALEOCLIMATE

Lipids from specific organisms can be used to reconstruct sea surface temperatures (SSTs) from ancient paleoenviroments. Biomarker temperature proxies are dependent on the specificity of their organismal sources, as well as the stability – both net community and physiological – of the relation between the lipids and the temperature signal over time. The two organic molecular classes most often used to reconstruct SSTs are the long-chain alkenones of haptophyte algae (Uk'37 proxy) and the tetraether lipids of marine Crenarchaeota (TEX86 proxy). The alkenone record extends to the Cretaceous, but the fidelity between contemporary calibrations and ancient alkenones remains unknown. Similarly, GDGTS that constitute the TEX86 proxy have the potential to be affected by many diverse sources of Crenarchaeota, both in the modern ocean as well as in ancient systems. In both cases, obtaining quality temperature reconstructions depends on (1) the physiological mechanism governing the biomarker-temperature function; (2) the degree to which community structure influences lipid distributions; (3) the mechanisms that transfers these signals to marine sediments; (4) the extent to which the signals are modified via diagenesis, in-situ production, or sediment redistribution; and (5) the taxonomic, ecophysiological, and evolutionary development of the specific compounds themselves. Despite these challenges, major achievements in understanding past climate regimes have been achieved with both of these classes of biomarkers.