Collaborative Research: Resolving Uncertainty in Past Delta-14C Spikes from Tree Rings

This collaborative project will use field- and model-based experiments to evaluate how different species of tree from different locations on earth take up and store carbon. Cosmic radiation, including particles from the sun, poses a serious threat to satellites, space stations, and human space exploration. Direct observations of extreme cosmic particle events are limited to the last several decades but environmental archives like tree rings and ice cores suggest that rare events can be ~50 times more severe than those documented by the instrumental record. Tree rings are globally common and record past events through isotopic tracers, yet the precision of these records may be affected by both latitude and the way different species take up and store carbon from the atmosphere. Results of this study will create an upper limit on extreme solar events critical for safeguarding space-based infrastructure from harmful cosmic events. This award support early-career researchers, graduate and undergraduate students, and women PIs from ESPSCoR states. Understanding past variability in Solar energetic particle events (SEPs) is critical for space-weather forecasting and safeguarding modern infrastructure. A well-replicated history of spikes in 14C from tree rings would provide an upper limit on severe space-based hazards yielding improvements in forecasting and risk assessment. However, inferences about the timing and magnitude of past 14C production is hampered by uncertainties associated with the role of non-structural carbohydrates (NSC) in the age of carbon allocated to wood. This project uses three of the best-replicated 14C spikes (663 BCE, 774 CE, and 993 CE) as global pulse-labeling experiments to quantify physiological sources of uncertainty on Δ14C measurements from tree rings with the goal of improving estimates of the nature of past 14C production spikes. Using living trees at three sites, the team will determine the age of carbon allocated to wood across three tree life strategies: evergreen conifers, deciduous conifers and deciduous angiosperms. The team will then pair these modern field measurements with new time series of past extreme 14C production events from the same sites and the global dataset of annual tree ring Δ14C measurements, to determine impacts of tree physiology and geomagnetic latitude on estimates of timing, duration, magnitude, and solar phase using a Bayesian framework for modeling 14C production from tree rings. Resolving sources of uncertainty in Δ14C in tree rings will yield better estimates of the magnitude past SEPs and create an upper limit on extreme solar events critical for safeguarding space-based infrastructure from harmful cosmic events. The Solar-Terrestrial Research Program, Paleoclimate Program, and GEO directorate co-fund this project. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.