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. Since the program’s launch in 2014, we have funded over 100 research projects.
Stable Isotopes in Leaf Wax n-Alkanes as a Record of Ambient Climate Through the Transition Into Soil Organic Matter
Abstract: The ratio of stable hydrogen isotopes (δ2H) in plant n-alkanes is linked to the isotopic composition of the precipitation they receive, which is tied to local geography and climate. Plant n-alkanes are retained through the transition into leaf litter and then into soils, which represent a long-term average of climate conditions recorded by the plant community. Ultimately plant n-alkanes are preserved in sedimentary rocks, allowing for them to be used as a paleoclimate proxy, providing insight into the local atmospheric δ2H at the time of deposition.
This project examines isotopic signals in plant leaf wax n-alkanes from across Washington State as a record of ambient climate conditions and their potential as a proxy for paleoclimate. The Cascade Mountains that run north-south through the Pacific Northwest create a strong rain shadow effect as precipitation from the Pacific Ocean is carried inward. The result is a stark difference in the climatic and growing conditions on the windward and leeward sides of the mountains. Western Washington is dominated by a moist temperate rainforest biome, while Eastern Washington consists of hotter, drier scrubland. Rainwater molecules containing heavier isotopes are rained out preferentially as clouds pass over the mountains, resulting in a ratio of relatively lighter isotopes on the east side and heavier on the west. As plants use atmospheric water as their primary source of hydrogen, this climatic and topographic marker is recorded in the hydrocarbon chains (n-alkanes) that make up their leaf waxes.
My goal is to assess the local trend of δ2H depletion across the Cascade Mountains’ orogenic gradient and to examine the pathway of this isotopic signature from plant tissue into soils. Duff plays an important role as the intermediate between plants and soil, but this pathway is largely understudied. This research serve to broaden our insight into the pattern of isotopic signals preserved from live plants into the soil and sedimentary rock record as well as into the climate of Washington State and its changes over time. With our results, we hope to refine isotopic methods of assessing paleoclimate through better understanding of modern biota and natural processes, including the poorly-studied pathway from live plant tissue to dead plant detritus to soil organic matter. Quantifying the isotopic fractionation that occurs in the transitional steps from precipitation to the rock record is crucial to expanding the potential of this method as a paleoclimate indicator.