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.
TREE BOLES REVEALED IN PACIFIC NORTHWEST LANDSLIDE DEPOSITS PROVIDE TREE-RING RECORD FOR PERIOD PRIOR TO DEGLACIATION The discovery of multiple large tree boles in landslide deposits dated prior to the last full-glacial period provides a new source for paleoclimatic data from the Northwest coast of North America. Realignment of U.S. highway 20 between Corvallis OR across the Oregon Coast Range onto Newport OR uncovered significant organic deposits at depth that include the boles of large trees. Radiocarbon dates on subsurface organic material from the project area range from 17,850 ± 100 to infinite ages >50 thousand years old (radiocarbon dates B.P.). Five large trees were recovered from one of an eventual seven road-cuts with the largest individual bole >1.2 meters (48 inches) in diameter. The sedimentary deposits are interpreted as paleo-translational landslides involving the movement along slip planes of sediments of the Tyee Formation. Preservation of the wood material and associated macrofossils is excellent, indicating that the deposits were sealed from any oxygen during their deposition. The first recovered bole (identified as Western Red Cedar; Thuja plicata) shows excellent preservation of late-wood rings with the early wood showing a high percentage of ghost tracheids. Ring counts from a portion of this bole, a four inch block of outer rings, contained between 120 to 130 rings of annual growth with good sensitivity for climate reconstruction. Eleven additional trees were discovered in a deposit together partially upright and they have all been identified as Douglas-fir (Pseudotsuga menziesii). These trees are more whole and larger in diameter than the recovered Western Red Cedar tree. A total of 11 trees were eventually recovered from this deposit and have all been identified as Douglas-fir. The tree rings were measured and correlated between the different boles. There were a total of more than 300 individual rings that cross correlated. The wood was in very good conditions and in most cases included pith and sapwood. Anatomical examination indicates it is all Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), which currently grows along the Pacific coast from central British Columbia to central California. All specimens crossdated and overlapped into a 297-year tree-ring width chronology, with no missing rings and a few very narrow pointer-years. The tree-ring width pattern contains several 3-year periods of growth reduction and concentration of resin duct formation in the earlywood. The tree-ring width series are highly variable with first-order autocorrelation up to 0.8 and mean sensitivity of 0.23. We also studied the variation of the Oregon Douglas-fir series using stable isotope series (d13C and d18O) to confirm the environmental signals in the tree-ring record from this deposit at this time. The variation in the rings of the ancient trees suggest that the trees come from a moisture-stressed environment, similar to that reported for modern Douglas-fir from the Canadian Cordillera and interior ranges of U.S. Rocky Mountains. Interestingly, the spatial pattern of modern tree-ring widths is consistent with the western dipole of moisture anomaly driven by El Niño. Today, tree rings in the area tend to show slower growth during Niño phases of ENSO because the Northwest tends to dry, less precipitation thus producing thinner rings. When ENSO is in a La Niña phase the region tends to be wetter and thus the trees build thicker rings. This is the first evidence in western North America for the existence of the ENSOpattern this far back into the past. The recovery of this collection of buried mature trees has provided an unique window into past regional climate prior to Marine Isotope Stage 3 (MIS3
