Abstract
Tree-ring records are invaluable sources of annually-resolved paleoclimate information that allow for the multi-centennial to multi-millennial contextualization of modern instrumental observations and trends. Within the Northern Hemispheric tree-ring record, substantial temporal and spatial limitations exist regarding the understanding of past temperature variability. In this body of work, I detail the refinement and application of the novel dendrochronological technique, blue intensity (BI), in order to develop a new network of tree-ring-based temperature proxy records across the mid-latitudes of North America. This dissertation, which heavily relies on the fundamental tree-ring principle of limiting factor, utilizes high-elevation tree-ring collections derived from Picea rubens and Picea engelmannii populations across the Appalachian, United States Rocky, and Sangre de Cristo Mountain ranges to examine the relationships between numerous tree-ring metrics (total ring-width, BI, and maximum latewood density) and climatic variables in temperature-limited montane environments. This body of work illustrates the first broad-scale application of BI methods as well as the first BI-based temperature reconstructions in North America below 45o latitude. In Chapter 1, I examine and demonstrate a strong, positive, and temporally stable relationship between late-growing season maximum air temperatures and the delta BI parameter using a P. rubens chronology from the southern Appalachian mountains of the eastern United States. In Chapter 2, I examine the application of using BI methods to create a composite latewood BI (LWB) P. engelmannii chronology from multiple sites across the Sangre de Cristo Mountains in northern New Mexico in order to develop a late-summer maximum temperature reconstruction for the southern Rocky Mountains that spans 1735-2015 CE. The reconstruction demonstrates fluctuating warm and cool periods during the latter portion of the Little Ice Age (ca. 1730-1850) and also documents substantial warming over the last decade, the trend of which appears to be anomalous within the context of the past ca. 280 years. In Chapter 3, I demonstrate the use of LWB to reconstruct current-year growing (warm) season maximum temperatures in the low-to-mid latitudes (30-50o N) of western North America. I detail the development of a new tree-ring network comprised of 26 LWB chronologies developed from living, high-elevation P. engelmannii sampled across the western United States. From this network, I develop 4 individual temperature reconstructions, which characterize regional temperature histories across western North America from northern Mexico to southern British Columbia over the past 4 centuries. Further, I compare these 4 temperature reconstructions to highlight the spatial patterns of regional temperature trends throughout time. This body of work and the subsequent reconstructions provide important updates and increased data point density to the tree ring temperature proxy network of the Northern Hemisphere. Additionally, I highlight the use of blue intensity methods at both low- and mid-latitude upper tree line locations to increase the presence of temperature-sensitive records at increasingly lower latitudes of the Northern Hemisphere. Finally, I conclude this dissertation with a brief synthesis detailing the current state of the global BI network and the anticipated future trajectory of BI methods within the paleoclimate community.