Isotopic record in a marine shallow-water core: imprint of solar centennial cycles in the past 2 millennia

The δ13C profile of Globigerinoides ruber, measured in the GT90/3 shallow-water Ionian sea core and dated with high precision, is presented and analyzed using the Singular Spectrum Analysis and the Wavelet Transform. This time series covers the period 200–1979 AD, with a resolution of 3.87 years. The δ13C of foraminifera depends on the photosynthetic activity of the symbiontic algae living on the shells, strictly related to the illumination of the sea-surface. Both spectral methods, besides an 11-years oscillation in phase with the Schwabe cycle of the solar activity, show the presence of a centennial cycle that is in phase with the amplitude modulation of the sunspot number series in the last 300 years. Moreover, another climatic record, the tree ring δ13C of a Japanese cedar covering the time interval 125–1952 AD, shows a similar centennial oscillation and therefore suggests that this climatic variation is global and in phase with the solar activity.