36Cl Concentrations from Polar Ice Cores Set New Constraints on the Carrington Event

TL;DR

This study uses 36Cl and other radionuclide data from ice cores to evaluate the Carrington event of 1859 CE, finding no evidence of a significant associated solar energetic particle event.

Contribution

It provides the first high-resolution 36Cl ice core records around 1859 CE, setting new constraints on the magnitude of solar events linked to the Carrington event.

Findings

No significant 36Cl increase around 1859 CE in ice core records.

Rules out a large SEP event with fluence above 30 MeV associated with the Carrington event.

Suggests either a smaller or no Earth-bound SEP event occurred in 1859.

Abstract

The Carrington event of 1859 CE is considered as one of the largest geomagnetic storms of the observational era, and often used as a benchmark for a worst-case scenario. Yet, there exists no robust evidence of an associated solar energetic particle event of a significant magnitude, based on measurements of cosmogenic radionuclides 10Be and 14C from ice cores and tree rings, respectively. In this study, we present two 36Cl records from Greenland with 2-year and 4-year resolution from the EGRIP and NGRIP ice-core sites, together with semi-annual 10Be data from EGRIP, as well as annual 10Be and 36Cl concentrations from the Dome Summit Site, Law Dome, East Antarctica. We observe no significant 36Cl concentration increase around 1859 CE in the three records. This allows us to rule out an extreme solar energetic particle event hitting Earth associated with the Carrington event in terms of fluence above 30 MeV. Based on these ice core 36Cl measurements, we can suggest two scenarios: i) a soft SEP event with a maximum fluence above 30 MeV up to three times larger than any Space Age event or, ii) the possibility that there was no Earth-bound SEP event.