This project tests the ability to reconstruct climate during Marine Isotope Stage 3 (MIS3) using sediments, pollen, and radioisotopic analysis of tree macrofossils recovered from a debris flow site in Oregon. Additionally, the researchers aim to explore the potential to use such logs that have measurable Carbon-14 to establish a floating chronological sequence to around 50,000 years.
The primary broader impacts involve extending radiocarbon dating back more than 12,000 years in fossil logs containing tree rings for climatic analyses. The research would be done in close collaboration with the Oregon Department of Transportation and its contractors, resulting in a strong interaction between the scientists and technical and engineering experts, although it was not clear how this would advance science and engineering in the next generation. Science results would become part of an outreach effort at the university and an Oregon state exposition. Graduate students from two universities (University of Arizona and California State University at Fresno) would be part of the research.
The warm Eemian interglacial period of the previous interglacial time, about 125,000 years ago, is similar to the current climate. It was followed by a long-term cooling that extended into the generally cold Marine Isotope Stage 3 (MIS 3, ca. 60 to 27 ka). Previous MIS 3 studies, largely from marine, ice core and lake records have informed us about the climate and climate variability of the period, but tree rings offer the potential for higher resolution reconstruction of the MIS 3 environments at annual or even finer time scales. The serendipitous discovery of wood estimated to be from this time period were discovered during the realignment of U.S. Highway 20 about halfway between Corvallis and Newport, OR. The trees had been buried by an ancient landslide and entombed in excellent condition until the highway project. A dozen large logs from trees that lived for hundreds of years were subsampled for tree-ring analysis. The studied subfossil logs indicate the potential of landslides as a source of well-preserved wood with high content of cellulose dated back into the Late Pleistocene prior to the Late Glacial Maximum. Additionally, organic and peaty sediments were sampled to identify plant and animal macrofossils and microfossils. The central goal of the study was to learn as much about environment and environmental variability from these materials as possible. Wood identification indicated that all trees are Douglas-fir, a species currently endemic to the region. A 297-year tree-ring "floating" chronology was developed from the trees by crossdating the patterns of large and small rings among the trees. Spectral analysis of the ring-width series shows evidence for an ENSO (that is, El Niño) influence on growth of the trees at this site >50,000 years ago, similar to that found in modern trees in the region. We also undertook isotopic studies to confirm the climatic effects and also embarked on a study of the radiocarbon content of these old wood samples. These studies were important to understanding the fluctuations in the radiocarbon record at this time. Broader Impacts: The chronologies developed in this study can be compared to other floating chronologies around this time in Chile and New Zealand and provide an inter-hemispheric and pan-Pacific perspective on environmental variability during MIS 3. Ultimately, these tree-ring chronologies might be used for high-precision radiocarbon analysis to help build the radiocarbon calibration curve. Additionally, the MIS 3 time period is generally cool, and this research allows comparisons with growth of modern Douglas-fir forests. Student training was important to improving STEM abilities for this project, and interactions with Oregon state agencies provided novel scientific analysis to their geologic interpretations. This interaction was of great benefit to the program.
