A conceptual and statistical framework for delineating the timing of a stratigraphic transition: Holocene-Anthropocene boundary as a case study

Abstract

The AWG (Anthropocene Working Group) proposed 1952 CE as the onset of the Anthropocene, marked by the detonation of the first hydrogen bomb, and designates Crawford Lake’s sediments in Canada as the potential stratotype. While the proposal for the Anthropocene as an epoch has been rejected by the SQS (Subcommision on Quaternary Stratigraphy), ongoing discussions regarding this debate remain unresolved. Here, we explore the possible biases and pitfalls of selecting the onset date from a singular site as the GSSP (Global boundary Stratotype Section and Point) for a chronostratigraphic boundary, using the potential Holocene-Anthropocene boundary as an example. We address the challenges of identifying changes in anthropogenic markers, along with the inherent measurement and age uncertainties, by employing a multilevel Bayesian change point analysis integrated with an errors-in-variables approach applied to proxy data. Our analysis utilizes plutonium isotopes (^(239+240)Pu), SCPs (spheroidal carbonaceous fly-ash particles), and radiocarbon (F¹⁴C) records from multiple locations established to evidence global anthropogenic imprints. Key findings include the identification of a population-level change point for ^(239+240)Pu at 1953 CE (1951.5–1954.5). While the standard practice for defining the onset date of a stratigraphic boundary typically involves selecting the date from the stratotype, our results suggest that 1953 CE should be the preferred date to define the onset of a potential Anthropocene Epoch. However, 1952 CE, which coincides with the first H-bomb test, cannot be statistically rejected as an alternative. Geographical clustering of SCPs data highlights regional variations in proxy signatures, while F¹⁴C results emphasize a lag of 5.5–9 years corresponding to carbon residence time. Our research contributes to discussions surrounding the delineation of a potential boundary between the Holocene and Anthropocene Epochs. Additionally, it provides methodological insights into identifying change points in multiple datasets and temporal lags in the environmental impacts of human activities.