On the common solar signal in different cosmogenic isotope data sets

In this article, we aim to determine frequency ranges and intervals of time in which the solar signal dominates in different cosmogenic isotope data. From a C-14-based reconstruction of cosmic ray intensity over the last millennia, we computed expected Be-10 variations in two Antarctic sites (Dom Fuji and South Pole) and two Greenland sites (Dye-3 and GISP-2) and compared them with the actually measured Be-10 abundance at the sites. By applying different methods of analysis, such as bivariate correlation, conventional FFT coherence, and wavelet coherence, we found the following: (1) The modeled series, on the basis of C-14 data, are in good agreement with the measured Be-10 data sets, on different timescales and at different locations, confirming the existence of a common solar signal in both isotope data. (2) The Be-10 data are driven by the solar signal on timescales from about 100 years up to 1000 years or even to multimillennial scales (at the longer scales, paleomagnetism plays an increasingly important role). (3) The local climate dominates the Be-10 data mostly on short (< 100 years) timescales, but the solar signal becomes important even at short scales during periods of Grand minima of solar activity. (4) There is an indication of a possible systematic uncertainty in the early Holocene, likely due to a not-perfectly-stable thermohaline circulation, which requires additional studies. We have shown that both C-14- and Be-10-based records are consistent with each other over a wide range of timescales and time intervals. They form a robust basis for quantitative reconstructions of solar activity variations in the past.