TREE-RING EVIDENCE OF NORTH PACIFIC VOLCANICALLY FORCED COOLING AND DROUGHT IN MIDWESTERN NORTH AMERICA

The drought of summer 2012 highlights the importance of understanding the hydroclimate of the Midwest, which includes examining linkages between North Pacific and Midwest teleconnections. Two volcanically-forced events provide a natural experiment for investigating the Pacific/ North American Teleconnection, and the hydroclimatic relationship between these two regions. Evidence is seen for undocumented volcanic eruptions in 1698/9 and 1809/10 in tree rings and ice cores, however, the origins of the eruptions are uncertain. Temperature-sensitive trees in the North Pacific give insight into especially cold springs and summers, which can force, or at least coincide, with dry summers seen in precipitation-sensitive trees in the Midwest. Previous studies have utilized dendrochronological evidence including narrow rings, low density rings and frost rings to identify volcanic events, which can then be compared to acidity peaks in ice cores. Both the 1698/9 and the 1809/10 events show narrow tree-rings and low latewood density for several consecutive years, signs of volcanic activity. Both events also occur during solar minima, the Maunder Minimum (1645-1715) and the Dalton Minimum (1790-1830). Multiple chronologies of ring width data from mountain hemlock, western hemlock, Alaskan cedar and sitka spruce trees, and a limited number of density chronologies from the Gulf of Alaska, as well as white oak ring-widths series from Northeastern Ohio all show these possible events, suggesting the possibility that ocean and atmospheric circulation patterns link these two locations. Identifying the forcing of these events can potentially be used in historical studies that seek to explain environmental conditions during European settlement of the Midwest, as well as offer predictive power in anticipating drought.