Increasing Tephra Deposition in Northeastern North America Points to Atmospheric Circulation Changes at the Early Mid Holocene Transition

The number of cryptotephra (non‐visible volcanic ash) records from northeastern North America is unique in the continent. The resulting tephrostratigraphic framework includes ash deposits sourced from volcanic arcs across the Northern Hemisphere and is an exceptional resource for correlating and dating paleoenvironmental records. It also provides an opportunity to explore more novel questions regarding the controls on ultra‐distal tephra (volcanic ash >3,000 km from source) dispersal and deposition. Here, we examine temporal patterns in the tephrostratigraphy of northeastern North America to test the legitimacy of a previously noted change in ash deposition frequency at the Early Mid Holocene transition. We integrate five new cryptotephra records into the existing framework to improve its temporal and spatial extent and report further occurrences of widespread cryptotephra deposits including Mt. St. Helens We, Jala pumice, White River Ash east, Ruppert tephra, Mt. St. Helens Yn and Mazama Ash. Reexamination of the combined tephrostratigraphy using breakpoint analysis shows a significant increase in the frequency of ashfall after ca. 9,000 (7,860–9,650) cal yr BP (calendar years before C.E. 1950). We discuss this change in relation to volcanic and environmental controls of fine ash dispersal and preservation. We reject hypotheses relating to eruption frequency or depositional processes in favor of changing atmospheric transport patterns and tephra dispersal—possibly caused by the retreat of the Laurentide Ice Sheet. Our study is a novel example of how tephrostratigraphy can be used beyond traditional correlative and dating studies, in this case indicating large‐scale changes in atmospheric circulation through time. Microscopic volcanic ash beds can be traced across continents and in northeastern North America have been extensively studied to form a stratigraphic framework of ashfall spanning the last 16,000 years. In this study, we extend the spatial and temporal extent of this framework and use statistical breakpoint analysis to look for patterns in ashfall frequency through time. We find that there is a sustained increase in the frequency of ashfall around 9,000 years ago. This pattern is inconsistent with wider records of volcanism and depositional processes and can only be explained by changes in atmospheric circulation. Paleoenvironmental records also show evidence for atmospheric changes that were driven by the collapse of the North American ice sheets. Our findings show that distal records of ashfall are sensitive to long‐term atmospheric change and can provide new data for testing paleoclimate simulations. New records and statistical reanalysis reveal an increase in tephra deposition frequency over northeastern North America ca. 9,000 years agoThis increase likely reflects changing atmospheric circulation associated with the collapse of the Laurentide ice sheet New records and statistical reanalysis reveal an increase in tephra deposition frequency over northeastern North America ca. 9,000 years ago This increase likely reflects changing atmospheric circulation associated with the collapse of the Laurentide ice sheet