Cosmogenic Radionuclide Evidence for a Solar Particle Storm at 14,300 BP

Abstract

Solar Energetic Particle (SEP) events, resulting from intense solar eruptions, can trigger significant short-term increases in the production of cosmogenic radionuclides such as 10Be, 14C and 36Cl. This thesis investigates the potential occurrence of SEP events around 14,300 and 14,700 BP, prompted by pronounced excursions previously identified in 10Be and 14C records. To examine these intervals in greater detail, high-resolution 10Be and 36Cl measurements from the North Greenland Ice Core Project are analysed to evaluate whether these peaks reflect SEP event signatures. The record presented here reveals one of the largest 10Be and 36Cl production peaks identified to date at 14,300 BP, which is mirrored by a concurrent spike in modelled 14C production rates. This consistent signal strongly suggests a link to an extreme solar event. The observed concentration variations exhibit a distinct ~11-year periodicity, corresponding to the solar activity cycle. This places the event within a period of high solar activity, which aligns with modern observations that SEP events are most prevalent near solar maxima. The 36Cl/10Be ratio of the excursion indicates a hard energy spectrum, characterised by a particle flux dominated by high-energy SEPs. Fluence estimates demonstrate that this event was of an outstanding magnitude, far surpassing any observed during the instrumental era. In contrast, no conclusive spike was detected in the interval centring around 14,700 BP. Variability in the radionuclide record during this time is likely connected to climatic fluctuations, rather than solar phenomena.

Popular Abstract

Investigating Solar Storms from over 14,000 years ago
Solar storms occur when the Sun releases bursts of highly energetic particles, known as Solar Energetic Particles (SEPs), into space. Occasionally, these storms are strong enough that the SEPs reach Earth, where they interact with particles in our atmosphere and cause a sudden spike in the production of radioactive isotopes like beryllium-10 (10Be), carbon-14 (14C), and chlorine-36 (36Cl). These isotopes are eventually deposited on Earth, where they are stored in natural archives such as ice cores or tree rings. Because these archives are precisely dated, stretching back tens of thousands of years, they allow us to measure past levels of these isotopes and thereby reconstruct past solar activity. Understanding when and how often these events happened, and how powerful they were, is important as they pose serious risks to astronauts, satellites, and electrical systems on Earth.
This study investigates two possible ancient solar storms around 14,300 and 14,700 BP (‘Before Present’, where ‘Present’ refers to the year 1950 CE), as this time interval has not been researched before and we can see from lower-resolution isotope records that there seems to be a spike there. This was done by extracting 10Be and 36Cl from a Greenland ice core. Their respective concentrations were measured using highly sensitive instruments. From this data, a timeline was created showing how the levels of these isotopes varied over the researched timespan.
Before interpreting the records, it was important to check the record for potential climate influences, as changes in snowfall can affect isotope concentrations in ice cores: increased snowfall dilutes the signal, while less snowfall amplifies it. This means a concentration spike could reflect either a solar storm or simply reduced snowfall. This effect was evaluated by assessing whether there was a correlation between the isotope concentrations and past temperature data from the same ice core. In polar regions like Greenland, higher temperatures generally lead to increased snowfall. No link was found between concentrations and climate during the interval surrounding the 14,300 BP interval, while there was a clear connection around 14,700 BP. This means that climate effects have to be considered for the latter. After doing so, it was confirmed that a major solar storm occurred around 14,300 BP. According to the new data, this storm appears to have been exceptionally intense and marked by very high-energy SEPs. It was far more powerful than any event recorded since instrumental measurements on Earth began, and ranks among the strongest ever detected in ice records. Aside from solar storms, 10Be and 36Cl are normally produced in our atmosphere by particles from outside our solar system. The Sun’s magnetic field acts as a shield blocking these particles, so during high solar activity, fewer reach Earth, but during quiet solar periods, more get through and generate isotopes. The data shows the 14,300 BP solar storm happened during a time of high solar activity, which agrees with modern observations that solar storms usually occur during these active periods.
In contrast, no conclusive evidence was found for a similar event at 14,700 BP. This appears to be a time where climate had a large influence on 10Be and 36Cl concentrations. This means that the data from this time period is too difficult to interpret, which makes it hard to see any clear signs of a solar storm. If a solar storm did happen, its effects are hidden by the natural climate changes that were also happening then.

• author: Raas, Valérie Victoria Maria
• supervisor: Raimund Muscheler
• organization: Department of Geology
• course: GEOR02 20251
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Earth and Environmental Sciences
• keywords: cosmogenic radionuclides, ice core, solar energetic particles, solar storm
• publication/series: Dissertations in Geology at Lund University
• report number: 719
• language: English
• id: 9207662
• date added to LUP: 2025-07-31 11:27:57
• date last changed: 2025-07-31 11:27:57