This award uses funds, under the auspices of the Small Grants for Exploratory Research (SGER) program, to conduct an exploratory investigation of the oxygen isotopic composition of cellulose extracted from annual tree rings from long-lived trees that grow along western margin of North America. This exploratory investigation is intended to determine if there is a coherent oxygen isotope record of oxygen-18 change recorded in the cellulose of trees distributed on the western U.S. margin. Specifically, the researcher will measure oxygen isotopes on the cellulose extracted from the annual rings of four trees at different locations in California.
Initial oxygen isotopic work on Bristlecone Pine cellulose, that covers the past two centuries, have concluded that the oxygen-18 signal of cellulose extracted from annual Bristlecone Pine samples indicates there was a large (10 per mil) negative shift in the oxygen-18 of precipitation falling on the site at the end of the 19th century and the early 20th century. The timing of this oxygen isotopic shift corresponds with the end of the Little Ice Age, a period of lower atmospheric temperatures across much of the northern hemisphere.
The researcher suggests that the oxygen isotopic shift recorded in the cellulose is related to the climatic changes and suggests that this involved a shift in the source of atmospheric moisture. Yet, he and his colleagues modeled the physiologic and the environmental parameters that influence the fractionation of oxygen isotopes in the cellulose and found that a 10 per mil shift would not be explained by either a change in temperature or a change in humidity at the tree site. The researcher hypothesizes that the isotopic shift would appear to require that prior to the 20th century the primary source of moisture to the Bristlecone Pine site in the White Mountains of California was from subtropical latitudes whereas during the 20th century the primary source has been from higher northerly latitudes. It is this hypothesis, among others, that the research will address.
The research could have broad impact on the wider science community and catalyze new thinking in issues surrounding climate by offering a new perspective on old and knotty scientific problems. The activities fit well into the potentially transformative, high risk, and exploratory nature of the SGER program.
