Persistence of the Gleissberg 88‐year solar cycle over the last ∼12,000 years: Evidence from cosmogenic isotopes

Among other longer‐than‐22‐year periods in Fourier spectra of various solar–terrestrial records, the 88‐year cycle is unique, because it can be directly linked to the cyclic activity of sunspot formation. Variations of amplitude as well as of period of the Schwabe 11‐year cycle of sunspot activity have actually been known for a long time and a ca. 80‐year cycle was detected in those variations. Manifestations of such secular periodic processes were reported in a broad variety of solar, solar–terrestrial, and terrestrial climatic phenomena. Confirmation of the existence of the Gleissberg cycle in long solar–terrestrial records as well as the question of its stability is of great significance for solar dynamo theories. For that perspective, we examined the longest detailed cosmogenic isotope record—INTCAL98 calibration record of atmospheric 14 C abundance. The most detailed precisely dated part of the record extends back to ∼11,854 years B.P. During this whole period, the Gleissberg cycle in 14 C concentration has a period of 87.8 years and an average amplitude of ∼1‰ (in Δ 14 C units). Spectral analysis indicates in frequency domain by sidebands of the combination tones at periods of ≈91.5 ± 0.1 and ≈84.6 ± 0.1 years that the amplitude of the Gleissberg cycle appears to be modulated by other long‐term quasiperiodic process of timescale ∼2000 years. This is confirmed directly in time domain by bandpass filtering and time–frequency analysis of the record. Also, there is additional evidence in the frequency domain for the modulation of the Gleissberg cycle by other millennial scale processes. Attempts have been made to explain 20th century global warming exclusively by the component of irradiance variation associated with the Gleissberg cycle. These attempts fail, because they require unacceptably great solar forcing and are incompatible with the paleoclimatic records.