QRC members lead and participate in a wide range of disciplinary and interdisciplinary research projects from the study of past earth climates and glaciations to shifts in the geographic distributions and evolution of vegetation and faunal communities, to the evolution and dispersals of the genus Homo and the increasing scales of human modification of earth environments through the Holocene. QRC provides a venue for meeting and collaborating with scholars across Quaternary disciplines. We are also fortunate to be able to provide seed funding and small grants for member research projects. We are especially happy to support grad student and junior scholar research activities, much of which leads to larger, external funding from agencies like the National Science Foundation.
Rainshadow Effect on Stable Isotopes of n-Alkanes across the Cascade Mountains of Washington, USA
Abstract: The Cascade Mountains, which run north-south through Oregon and Washington into British Columbia, are one of the dominant geographic features of the Pacific Northwest. This project seeks to examine the stable-isotopic orographic rainshadow effect produced by the Cascades by comparing the d2H (dD) and d13C of n-alkanes (a long-chain hydrocarbon found in the waxy cuticles of plant leaves) from living plants, leaf detritus, and soil organic matter in a transect across the Cascades of Washington state. The dD of a plant is dominantly dependent on the dD of local rainfall, while the d13C depends mainly on the species of the plant and the aridity of its environment; the dD and d13C of n-alkanes in the soil depend on the plants which have contributed leaf litter to that soil. Documenting how the Cascade rainshadow affects and/or controls hydrogen and carbon isotopic trends is critical to understanding the fate of atmospheric moisture when it passes through orogens, and how plants (and soils) react to those changes. Moreover, understanding how isotopic trends evolve across the Cascade rainshadow is a mandatory step towards documenting the topographic evolution of the Cascades through geologic time via isotopic proxies. Identifying the nature of the isotopic trends – for instance, where and how transitions in isotopic composition occur – will allow us to determine if the degree and trend of isotopic depletion is directly correlated to rainshadow intensity and, by extension, the Cascades’ topography. This will provide a dataset for researchers studying isotopic distillation both by plants and by atmosphere dynamics, and a modern comparator for studies of ancient isotopic trends in this and similar settings.
Paleoenvironmental constraints from paleosol-loess sequences: evaluating clumped (∆47) isotopic records in biogenic and pedogenic carbonate
Abstract: The goal of the proposed work is to advance understanding of how the geochemistry of biogenic and pedogenic (formed in soil) carbonates record surface environmental temperatures and soil water compositions relevant to the interpretation of proxy records in Quaternary loess-paleosol sequences and cultural layers. Reconstructing Quaternary paleoenvironments is important for a broad range of paleoclimate, geology, biology, anthropology and archaeology studies. To this end, the geochemistry of carbonate minerals formed at and near the Earth surface can provide quantitative environmental constraints including the δ18O values of water, δ13C-based information about vegetation, and most recently, estimates of Earth-surface temperatures from clumped isotope (∆47) thermometry. Early efforts to develop clumped isotope thermometry in modern-Holocene soils raise many questions about how to interpret not only ∆47 temperatures but also conventional δ18O and δ13C values in soil and loess carbonates. Specific issues include seasonal bias in carbonate growth and vital effects in biogenic carbonate. We must address these issues in order to understand and exploit these valuable archives of environmental information preserved in paleosols and cultural layers.
The project will benefit Quaternary research by refining and developing new methods for reconstructing terrestrial Quaternary climate change from loess-paleosol sequences and environmental context from cultural layers, and benefit the intellectual life of the QRC through enhanced international visibility and exchange, support of facilities and research that benefit QRC members, and training of future Quaternary scientists.
Abstract: The Cascade Mountains, which run north-south through Oregon and Washington into British Columbia, are one of the dominant geographic features of the Pacific Northwest. This project seeks to examine the stable-isotopic orographic rainshadow effect produced by the Cascades by comparing the d2H (dD) and d13C of n-alkanes (a long-chain hydrocarbon found in the waxy cuticles of plant leaves) from living plants, leaf detritus, and soil organic matter in a transect across the Cascades of Washington state. The dD of a plant is dominantly dependent on the dD of local rainfall, while the d13C depends mainly on the species of the plant and the aridity of its environment; the dD and d13C of n-alkanes in the soil depend on the plants which have contributed leaf litter to that soil. Documenting how the Cascade rainshadow affects and/or controls hydrogen and carbon isotopic trends is critical to understanding the fate of atmospheric moisture when it passes through orogens, and how plants (and soils) react to those changes. Moreover, understanding how isotopic trends evolve across the Cascade rainshadow is a mandatory step towards documenting the topographic evolution of the Cascades through geologic time via isotopic proxies. Identifying the nature of the isotopic trends – for instance, where and how transitions in isotopic composition occur – will allow us to determine if the degree and trend of isotopic depletion is directly correlated to rainshadow intensity and, by extension, the Cascades’ topography. This will provide a dataset for researchers studying isotopic distillation both by plants and by atmosphere dynamics, and a modern comparator for studies of ancient isotopic trends in this and similar settings.