Extremely large variations of atmospheric 14C concentration during the last glacial period

A long record of atmospheric C-14 concentration, from 45 to 11 thousand years ago (ka), was obtained from a stalagmite with thermal-ionization mass-spectrometric Th-230 and accelerator mass-spectrometric C-14 measurements. This record reveals highly elevated Delta C-14 between 45 and 33 ka, portions of which may correlate with peaks in cosmogenic Cl-36 and Be-10 isotopes observed in polar ice cores. Superimposed on this broad peak of Delta C-14 are several rapid excursions, the Largest of which occurs between 44.3 and 43.3 ka. Between 26 and 11 ka, atmospheric Delta C-14 decreased from similar to 700 to similar to 100 per mil, modulated by numerous minor excursions. Carbon cycle models suggest that the major features of this record cannot be produced with solar or terrestrial magnetic field modulation alone but also require substantial fluctuations in the carbon cycle.