Reconstructing Annual Δ14C During Miyake Events Using Deciduous and Evergreen Trees

Abstract

Cosmic rays and solar energetic particles pose significant risks to satellites, space stations, and human space exploration. They also produce atmospheric radiocarbon (¹⁴C), which enters the carbon cycle and is recorded by paleoenvironmental proxies. Miyake events, rapid increases in atmospheric ¹⁴C, first identified in annual tree rings and later confirmed through ice core ¹⁰Be and ³⁶Cl isotopes, are thought to result from extreme solar activity, are seven events identified over the last 14,300 years. However, uncertainty in annual ¹⁴C measurements limits precise inferences about their timing and magnitude. This study examines uncertainties in ¹⁴C during two Miyake events (774 CE and 993 CE) across trees with differing uptake, storage, and allocation of carbon. We hypothesize that tree species physiology affects tree-ring Δ¹⁴C, with deciduous species recording lagged, attenuated tree-ring Δ¹⁴C relative to evergreen species. Using Δ¹⁴C data from pine and larch in Mongolia and a larger multi-species Northern Hemisphere data set, we employed a Bayesian framework to estimate the timing, duration, and magnitude of these two events. Our AMS results showed no differences in Δ¹⁴C between evergreen and deciduous species growing at similar sites during the 774 CE event. The 993 CE event was variable, but parameter estimates were consistent between species. Northern Hemisphere comparisons indicated that annual series of Δ¹⁴C from evergreen and deciduous conifers yielded relatively more precise modeled estimates of start date and duration relative to deciduous broadleaf species. Future studies should consider the role of species-specific carbon allocation strategies and storage dynamics in determining the radiocarbon response to Miyake events.