Radiocarbon measurements on tree rings (969-1933 AD)

Accelerator mass spectrometer measurement results of C14 age in tree rings from 13 different dendrochronoligically dated trees from England and Switzerland spanning the last almost all of the last millenium.

The Sun provides almost all of the external forcing to the Earth system, so that its variability is of considerable interest for geoscience. Observational records of solar activity cover only the last about 400 yr. Beyond that, cosmogenic nuclides stored in tree rings (14C) or ice cores (10Be, 36Cl) are used as proxies for solar activity extending back by many thousands of years1-3. Major drawbacks of cosmogenic nuclide based solar reconstructions are the presence of weather-induced noise (10Be in ice cores) and/or low temporal resolution of long, precisely dated records (14C in tree rings). Here, we present a continuous, annually resolved 14C record from absolutely dated tree rings covering nearly all of the last millennium (969-1933 AD). The high resolution and high precision 14C record reveals the presence of the eleven-year solar Schwabe cycle over the past millennium. Statistical analysis of the Schwabe cycle shows a positive correlation of its amplitude with reconstructed solar modulation. The record further confirms the 993 AD solar energetic particle event and reveals two new candidate events (1052 AD and 1279 AD) indicating that strong solar events are probably more common than previously thought.