ARTHUR L. DAY MEDAL: ISOTOPE PATTERNS WITHIN BIOMARKERS

Stable isotope analyses of individual fossil molecules, or biomarkers, are central to studies of paleoclimate and carbon cycle dynamics on land and in ocean and aquatic environments over Earth’s history. While measurements of isotopes in whole molecules can now be achieved for picomolar quantities, a 100-times drop since its introduction 30 years ago, even more powerful analytical tools have expanded our access to isotope patterns that are present within organic and inorganic compounds. Significant isotope variability among atom positions within molecules has been long recognized but hard to measure. New methods using high-mass-accuracy and high-mass-resolution mass spectrometry open ways to interrogate biotic and abiotic influences on individual atoms within biomarker compounds. Such signatures are sensitive to processes within organisms, in their habitats over Earth’s history, and potentially in planetary environments. Such isotopologue studies have potential to enrich our understanding of biogeochemical signatures carried by the diverse inventory of organic compounds preserved in ancient sediments. Position-specific isotope signatures carried from glucose and other substrates into lipids that become biomarkers open the possibility of tracking internal “fingerprints” among individual atoms that distinguish otherwise structurally similar compounds from distinct biological sources or reveal the influence of climatic and environmental influences on growth conditions.