Date of Graduation
Doctor of Philosophy in Geosciences (PhD)
Second Committee Member
Third Committee Member
ENSO, latewood, paleoclimate science, precipitation, reconstruction, variability
Earlywood (EW) and latewood (LW) ring-width chronologies have become an increasingly important proxy in paleoclimate reconstructions. These subannual variables can provide estimates of past hydroclimate variability for seasonal windows that total ring-widths cannot resolve. The strength of the relationship between EW and LW series may influence what type of paleoclimate information is embedded within the tree-ring series. High correlations (> 0.70) between EW and LW are recorded for much of the continent but the magnitude of correlation varies greatly across space and species boundaries. Using four LW chronologies from shortleaf pine, the North American conifer species displaying the lowest EW-LW correlation, a reconstruction of summer atmospheric moisture balance spanning the years 1685-2015 was produced for the central United States. A second reconstruction, based on ten EW and total-ring width chronologies from three other species, estimates May soil moisture for the same period. The relationship between reconstructions displays strong decadal swings in both instrumental and reconstructed data that could potentially improve forecasting skill of summer rainfall. The Atlantic Multidecadal Oscillation (AMO) appears to dictate the changing persistence in seasonal hydroclimate and the reconstructions suggest that this ocean-atmosphere forcing has been a stable feature of North American climate dynamics over the past 300 years. Finally, this dissertation investigates the temporal stability of El Niño-Southern Oscillation (ENSO) signals in the North American tree-ring network in relation to AMO phasing. Numerous reconstructions of ENSO have been produced relying on tree-ring chronologies from the American Southwest as predictors, however, the teleconnection between ENSO and local hydroclimate has varied in strength and spatial expression during the 20th and early 21st century. There is a significant loss of tree-ring records exhibiting significant correlations with ENSO during subperiods associated with the negative phase of the AMO. A new reconstruction, relying solely on a subset of chronologies with time-stable ENSO signals, was produced. When compared to the North American Drought Atlas for the past 350 years, similar expansions and retractions of ENSO influence from the core region of northern Mexico and the border states of the United States seen in the instrumental period/data are recorded.
Torbenson, Max Carl Arne, "Cool and Warm Season Climate Signals in Tree Rings from North America" (2019). Theses and Dissertations. 3225.