A radiocarbon spike at 14 300 cal yr BP in subfossil trees provides the impulse response function of the global carbon cycle during the Late Glacial

Abstract

We present new 14 C results measured on subfossil Scots Pines recovered in the eroded banks of the Drouzet watercourse in the Southern French Alps. About 400 new 14 C ages have been analysed on 15 trees sampled at annual resolution. The resulting Δ 14 C record exhibits an abrupt spike occurring in a single year at 14 300–14 299 cal yr BP and a century-long event between 14 and 13.9 cal kyr BP. In order to identify the causes of these events, we compare the Drouzet Δ 14 C record with simulations of Δ 14 C based on the 10 Be record in Greenland ice used as an input of a carbon cycle model. The correspondence with 10 Be anomalies allows us to propose the 14.3 cal kyr BP event as a solar energetic particle event. By contrast, the 14 cal kyr BP event lasted about a century and is most probably a common Maunder-type solar minimum linked to the modulation of galactic cosmic particles by the heliomagnetic field. We also discuss and speculate about the synchroneity and the possible causes of the 14 cal kyr BP event with the brief cold phase called Older Dryas, which separates the Bølling and Allerød millennium-long warm phases of the Late Glacial period. This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'.

A special issue preface: Radiocarbon in the Anthropocene

“…The final paper in the theme issue by Bard et al [ 9 ] reports annual-resolution 14 C measurements on tree rings from subfossil Scots Pines from the Southern French Alps in the context of past atmospheric 14 C variability spanning a 700-year interval during the Late Glacial period. The record reveals two prominent events that are attributed to solar activity, providing further linkages with Greenland ice core records and temporal context for interpretation of past climate variability.…”

Review of the August 1972 and March 1989 (Allen) Space Weather Events: Can We Learn Anything New From Them?

“…It has also recently been shown that extreme solar particle events may have occurred in the distant past (775 CE, 994 CE, 660 BCE, and 7176 BCE) using cosmogenic isotopes ( 10 Be, 36 Cl, and 14 C) detected in tree ring and ice core data (Brehm et al, 2022;Koldobskiy et al, 2023;Miyake et al, 2012Miyake et al, , 2019Usoskin et al, 2013). See also Bard et al (2023) for a possible event at 14,300-14,299 BP. These events have had peak fluxes that are one or two orders of magnitude higher than either the August 1972 or the March 1989 event (Koldobskiy et al, 2023).…”

Transient Offset in 14C After the Carrington Event Recorded by Polar Tree Rings

“…In addition to such long-term and large-scale phenomena, attention has recently been given to rapid and anomalous 14 C events discovered by Miyake et al (2012Miyake et al ( , 2013. The initial finding sparked considerable interest, leading to additional discoveries of rapid 14 C increases, all found through annually resolved tree-ring measurements (e.g., Bard et al, 2023;Brehm et al, 2022;Miyake et al, 2017Miyake et al, , 2021O'Hare et al, 2019;Paleari et al, 2022;Park et al, 2017;Terrasi et al, 2020). These events are short production increases in 14 C caused by extreme solar energetic particle (SEP) events (Cliver et al, 2022;Usoskin, 2023;Usoskin et al, 2013).…”