Towards Broad-Scale Temperature Reconstructions For Eastern North America Using Blue Light Intensity From Tree Rings

Summer temperatures across eastern North America (hereafter East) will soon reach a level consistently above any observation experienced during the instrumental period. Increasing temperatures will have negative impacts on natural (e.g., water, plant and animal communities) and human (e.g., health, infrastructure, economies) systems upon which the large and growing centres of human population across the region depend. Within the network of Northern Hemisphere tree-ring temperature proxy records, one of the most obvious geographic holes is the East, where few temperature-sensitive proxies exist. Here we present the first steps towards building a network of temperature-sensitive proxy records across the East using blue light intensity (BI) methods applied to the tree rings of multiple temperature sensitive tree species situated from North Carolina to Maine, USA. Our overall objective is to report on the most viable species for BI analysis across different regions of the East (e.g., Southeast US, Midwest US, Northeast US/Canadian Maritimes) by exploring temporal (e.g., since ca. 1900) and spatial relationships between instrumental temperatures and BI metrics. We found BI to be a strong predictor of March-October mean air temperature (R-2 = 0.61) across the Northeast US/eastern Canada, and Sep-Oct maximum air temperature (R-2 = 0.42) across the Southeast US. Of all species tested, Tsuga canadensis and Picea rubens contained the strongest BI temperature signal. Adding more BI sites from these and potentially other species, as well as inclusion of other temperature proxies (e.g., ring widths) will allow for the development of a skilful broad-scale and long-term temperature field reconstruction across the East.