Biomarkers
Certain molecular components of organic matter are resistant to degradation and are preserved in sediments. These organic molecules, known as biomarkers, constitute “molecular fossils” providing information on life in the geological record. Molecular abundance and isotopic compositions (carbon 13/12 and deuterium/hydrogen) provide useful information on source organisms and their environmental conditions, offering contributions to the fields of paleobiology, paleoecology and paleoclimatology.
Compound-Specific Isotopic Analysis
Stable isotopes are established chemical tracers for many climatic and ecological applications. Isotopic compositions can be measured at the molecular level, enabling detailed, high-resolution reconstruction of specific aspects of biological organisms and their environments. Isotopic analysis of biomarkers, commonly referred to as compound-specific isotopic analysis, offers many new possibilities for geological and biological research.
Carbon Isotopes
The stable isotopes of carbon (carbon 13/12) have been used to estimate changes in photosynthesis pathway, atmospheric carbon dioxide and various fluxes within the carbon cycle. Compound-specific isotopic analysis enables separation of compounds from constituent sources enabling more secure paleoenvironmental interpretations than can be achieved through bulk organic carbon analyses alone.
Hydrogen Isotopes
Analytical advances have only recently enabled the measurement of deuterium/hydrogen (D/H) ratios in individual organic compounds opening up possibilities for many new applications. Hydrogen isotopic compositions and fractionations offer insights into biogeochemical processes and changes in the hydrological cycle.
Analytical Methods
Molecular level analyses use organic geochemical laboratory techniques. Individual compounds are extracted from complex organic mixtures in lacustrine sediments by solvent extraction and column chromatography. Extracts are then analyzed with gas chromatography and mass spectrometry to assess molecular identity and isotopic composition. These molecular level analyses reveal specific biological components in the geological record and resolve details of the biotic community and abiotic environment. Facilities housed in the Feakins lab are detailed here.
Isotopic Tracers in Modern Environments
Molecular and isotopic compositions provide chemical tracers with which to follow organic molecules from source to sedimentary deposit and thus valuable tools to monitor a wide range of highly-specific and high-resolution biotic and environmental signals. Measurements of biogeochemical processes in the modern environment have implications for ecology, biochemistry and hydrology as well as proxy development and calibration needed to develop high-resolution, quantitative tools for paleoecological and paleoclimatic reconstruction.
Paleoenvironmental Reconstructions
Molecular level analyses can improve our understanding of paleoclimatic and paleoecological change. We are particularly interested in reconstructing natural climate variability over the past millennia. The frequency and severity of past wet-dry cycles in water-stressed California and Nevada are of great interest as we consider current and future water resources and climate hazards.
Current Research Questions
- Hydrogen Isotopes as a Paleohydrology Proxy
- Calibration studies of Hydrogen Isotopes in Californian vegetation
- Lacustrine records of late Holocene climate history
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