Annual rings of trees reveal strong solar storms

This indicates that a very strong solar storm, a type sometimes called Proton event, when the Sun ejects large amounts of charged particles with high energy. The increase in carbon-14 during this year appears to be more than double that of the second strongest known event of this type, which occurred in 774.

Relatively short-lived isotopes such as carbon-14 are created when radiation from space hits atoms in the air and changes some of them. Radiation varies due to both sudden solar storms and slow variations in the Sun’s magnetic field that shield some radiation from space outside the Solar System.

In the past, four strong solar storms were identified by carbon-14 levels in wood, and verified by measurements of other isotopes found in drill cores in glacial ice from Greenland.

Analysis of the ice six years ago already showed the highest content of the beryllium-10 isotope since this time 14,000 years ago. With samples from ice, the timing resolution is poor and it is not possible to tell whether it is a solar storm or a slow event. A new study could determine that.

– This gives a better dating because they are measured in annual rings and in principle the exact age can be known. They were able to see that the level of carbon-14 in the atmosphere rose from one year to the next, says Raymond Muscheler, professor of Quaternary geology at Lund University, who was involved in the analysis of the glacial ice.

By comparing annual rings on trees that vary in thickness from year to year, a time series can be created that can be used for dating archaeological finds. This is called Dendrochronology. Conversely, sudden increases in carbon-14 content can also be used to determine age when wood finds cannot be fit into dendrochronology. But mapping variations in carbon-14 can also provide knowledge about radiation from space.

– It is important to understand what the sun can do. How strong are solar storms? How often can they occur? Risk analysis of such events is important for our society, says Raymond Muscheler.

Such solar storms can endanger high-tech infrastructure in space and on Earth.

These types of studies are also valuable in calibrating the carbon-14 method. When this is used for dating, you need to factor in variations due to both radiation from space and the carbon cycle on Earth.