Searching solar periodicities in the late glacial record of atmospheric radiocarbon

Accelerator mass spectrometry radiocarbon (AMS C-14) dating of the late glacial section of laminated sediments from Lake Gosciaz and Lake Perespilno, Poland, performed with time resolution of 20-30 years suggests quasi-periodic oscillations of Delta(14)C. The regularity of oscillations has been checked by the Maximum Entropy and Fast Fourier Transform methods (MEM and FFT), which revealed peaks at 200 and 230 yr. These periods are similar to those found in the high-precision Holocene Delta(14)C record, and attributed to the changing sun. The analytical assessment of the significance of the FFT and MEM peaks is problematic because of non-uniform spacing and various uncertainties in the input data. The significance of the peaks has therefore been studied by the Monte-Carlo method. Because the original data were approximated with a spline function, the amplitude of the MEM and FFT peaks depends on the stiffness of the spline, which is strongly related to the real uncertainty of C-14 ages. The Monte-Carlo experiments demonstrate that the significance levels of the MEM and FFT peaks also depend on the spline stiffness. Therefore, the existence of solar (14)Cvariations in the Late Glacial remains an open question.