David A. Zinniker
Gaylord Donnelley Environmental Fellow
Yale Institute for Biospheric Studies
Department of Geology and Geophysics
Yale University
David A. Zinniker
Gaylord Donnelley Environmental Fellow
Yale Institute for Biospheric Studies
Department of Geology and Geophysics
Yale University
My research is innovative primarily in the application of CSIA techniques to taxon-specific molecular fossils and the utilization of unique sedimentary archives where they are abundant. This work is aimed at deriving interpretable isotope records that provide insights into past climate and biotic responses to changing environmental conditions, including but not limited to pCO2 and seasonal variations in temperature, precipitation, and relative humidity. My current work focuses on plant and microbial markers in fossil packrat middens, peats, and coals. This includes modern transects and ancient records across North America.
The stable isotopic composition of taxon-specific higher plant biomarkers in ancient packrat middens: Novel proxies for seasonal climate in the southwest U.S.
Fossil packrat middens in the southwestern US contribute critical details to our understanding of past climate change and floral migrations across geography and elevation. They provide detailed snapshots of the flora found in a packrat's range and a survey of pollen from a larger region, allowing unambiguous inferences to be made about changes in seasonal climate.
Our work is an intense effort to extend midden analysis to include taxon-specific molecular fossils. Archived midden materials, representing a significant investment of scientific funding and research effort, provide an opportunity to study taxon-specific plant and microbial lipids in well-dated late Pleistocene and Holocene samples with restricted and well-defined biological inputs.
The study is divided into three parts: (1) a chemical survey of common Neotoma food plants, (2) a molecular and isotopic investigation of fecal pellets in modern middens across a range of ecosystems, and (3) a molecular and isotopic study of fossil fecal pellets in ancient midden sequences from southern Arizona.
Preliminary results demonstrate the feasibility of identifying taxon-specific biomarkers for Pinaceae, Cupressaceae, Cactaceae, Zygophyllaceae, and Agavaceae within complex mixtures. Compound specific isotope analysis of these biomarkers reveals the existence of robust environmental signals for conditions during plant growth. Taxon-specific isotope analysis delineates the Bolling Allerød, Younger Dryas, and Holocene Climatic Optimum periods and reflects significant changes in the strength of the North American Monsoon, the southern limit of westerly storm tracks, and seasonal and/or mean temperatures.
The sensitivity of this molecular archive to conditions during plant growth (soil moisture, precipitation, temperature, relative humidity) will make it a useful and non-redundant addition to climate records in the US southwest. Results will compliment paleobotanical studies and constrain interpretations of higher resolution climate archives lacking sensitivity to seasonal climate.
Climatic and physiological controls on the stable isotope composition of modern and ancient Cupressaceae
Unique and abundant secondary metabolites found in waxes and resins of the Callitroid, Cupressoid, and Taxodioid clades of the Cupressaceae family can be identified and quantified in complex mixtures of sedimentary organic compounds. This unusual feature makes it possible to study relatively simple (taxon-specific) isotope systems back in time across the broad array of environments in which these conifers are found. Work on these systems can potentially provide both robust paleoenvironmental proxies (i.e. for source water δD and growing season relative humidity) and quantitative probes into the ecophysiology of these plants in modern and ancient environments.
Our research focuses on three genera representing environmental end-members of Cupressaceae -- Juniperus, Thuja, and Chamaecyparis -- (1) across geographic and environmental gradients in the field, and (2) in specific Holocene and late Pleistocene environmental records. The latter research focuses on peat cores from New England and Oregon and fossil packrat middens from the southwestern United States. Modern transects highlight the sensitivity of Cupressaceae to climatic variables. These include both variables during growth (relative humidity, soil moisture, etc.) and variables affecting seasonal and diurnal growth rates (temperature, winter precipitation, insolation, microhabitat, etc.). Work on ancient records has demonstrated the sensitivity of these unique taxon-specific archives to both subtle and dramatic climate shifts during the Pleistocene and Holocene.
This work will result in an improved understanding of climatic and physiological controls on the stable isotopic composition of modern and ancient Cupressaceae -- and by extension, other arborescent gymnosperms and C3 plants -- providing a framework for understanding more complexly sourced organic inputs to sediments, coals, and petroleum prior to the advent of C4 plants. This research also has direct implications for stratigraphic stable isotope studies of gymnosperm markers across the last millenium, the Pleistocene, and important climatic events in the Mesozoic and Tertiary.
PAST WORK
The major focus of my PhD research at Stanford was deciphering the complexity of terpenoid molecular fossils found in sediments, coals, and petroleum. The work involved molecular modeling and laboratory simulation of diagenetic processes; the creation of authentic standards using organic synthesis techniques; enrichment of target compounds using HPLC, adduction and molecular sieve techniques; the identification of compounds using NMR; and the recognition and quantification of compounds using sensitive GC-MSMS, GC-MRM, and GC-MS techniques. I also studied a diversity of other molecular fossils (saturated and aromatic biomarkers, branched alkanes, diamondoids, organic acids, phenols, organic sulfur compounds, PAH, alkenones, sterols, etc.) and worked on projects involving detailed stratigraphic analysis of microfossils (foraminifera, diatoms, palynomorphs) and bulk geochemical parameters.
CV available upon request