The 774–775 Carbon-14 Spike is an observed increase of 1.2% in the concentration of[carbon-14 isotope in tree rings dated to the years 774 or 775 CE, which is about 20 times as high as the normal background rate of variation. It was discovered during a study of Japanese cedar trees, with the year of occurrence determined through dendrochronology. A surge in a specific isotope of beryllium (10Be), detected in Antarctic ice cores, has also been associated with the 774–775 event.