Accelerator measurements of 10Be: The 11 year solar cycle from 1180-1800 A.D.

In order to investigate the extent to which 10Be concentrations in polar ice record solar activity on the level of individual Schwabe solar cycles, we have measured 10Be concentrations over the interval from 1180 to 1800 A.D. in an ice core from Greenland, using the accelerator mass spectrometer of the ETH Zurich. The data were analysed using the cyclogram method of time series analysis which showed that 10Be concentrations varied with a period which ranged between 9 and 11.4 y. Schwabe-type 10Be variations were visible even during the Maunder Minimum (1645–1715 A.D.), an interval of almost no visible sunspots. During this period 10Be concentrations varied with a periodicity which slowly increased from 9 to 11 y. 10Be concentrations were higher during the Maunder Minimum than during minima in the 11 y Schwabe cycle. This suggests the presence of residual solar modulation even during Schwabe solar cycle minima