c) The spectral power distribution of a 2000-yr window centered at 4,525 BP, showing the Gleissberg cycle (~ 88 yr) as the most dominant feature in this frequency range for the 3,500-6,500 BP period. It is also very unlikely that we will be able to determine if it played a significant role in the climate of the period.

The result is reproduced using a Be solar activity reconstruction. As the evidence indicates this periodicity is not currently relevant, we will not consider it further.

a) Solar sunspot number reconstruction from cosmogenic C isotopes. b) Wavelet analysis of the sunspot number reconstruction, with the Eddy periodicity indicated by a continuous line, and the Bray periodicity by a dashed line. a) Solar sunspot number reconstruction from cosmogenic C isotopes. Blue curve, inferred iceberg activity in the North Atlantic (inverted) from petrological tracers. Other researchers have found that applying the trapezoidal filter of Gleissberg separately to dates of solar cycle minima and maxima from sunspot records then merging them, one also obtains an ~ 80-year time domain periodicity (Peristykh & Damon, 2003).

Introduction In a recent review of Holocene climate variability (Part A, and Part B) it was shown that Milankovitch forcing was likely the primary driving force behind the general climate evolution from the Holocene Climatic Optimum to the Neoglacial period, for the past 12,000 years. The last three warm periods (orange bars) and 2 cold periods (blue bars) are indicated. E12 (11,250 BP) coincides with a particularly humid phase in northwestern and central Europe towards the end of the Preboreal oscillation (van der Plicht et al., 2004; Magny et al., 2007). This finding has been confirmed for tree-rings, which reflect changes in temperature or precipitation, in several regions of the planet. (2017) have constructed a tree-ring multi-proxy (54 series), extra-tropical Northern Hemisphere, warm season (MJJA), temperature record spanning 1,200 years (750-1988 AD). Arrows indicate the phase of the relationship where coherence 0.65. Band-pass filtered total solar irradiation (dotted red line) and tree-ring-derived climate data series in the range of periods 180–230 years for (a) Asia, and (b) Europe. Other studies link the 208-year de Vries cycle to climate change, including Central Asian ice-cores (Eichler et al., 2009), Asian (Duan et al., 2014) and South American (Novello et al., 2016) monsoon-record speleothems, Mesoamerican lake-sediment cores as drought proxies (Hodell et al., 2001), and Alpine glaciers (Nussbaumer et al., 2011).

Additionally, the ~ 2400-year Bray climate cycle (Part A), of solar origin (Part B and Part C), appears responsible for the main climatic subdivisions of the Holocene, and the climatic pessima that separate them, such as the Little Ice Age. E11 (10,300 BP) coincided with the first cold, humid event, of the Boreal phase (Björck et al., 2001; Magny et al., 2004b), while E9 (9,300 BP) matches the second Boreal event (Rasmussen et al., 2007; Magny et al., 2004b). The identification of the Eddy cycle lows, as well as the Bray cycle lows (figure 64), allows an examination of grand solar minima (GSM) distribution according to the two main solar cycles of the Holocene. The record shows high and stable coherence and consistent phasing with solar irradiance estimates at bi-centennial time scales (194-222-year periods), the ~ 208-year de Vries solar cycle frequency (figure 84; Anchukaitis et al., 2017). Bi-centennial solar influence on Northern Hemisphere summer temperatures from tree-rings. b) Wavelet coherence between the Northern Hemisphere mean MJJA temperature anomaly time series and solar forcing variability from Vieira and Solanki (2010), Astron. In-phase signals point directly to the right of the plot. The values in the brackets describe the variability in the band-pass filtered time series in relation to the corresponding unfiltered data series for the displayed time intervals. The climatic effect of the de Vries solar cycle is thus well established.

The ~ 208-year de Vries cycle has been detected in ice-cores for at least the past 50,000 years (Raspopov et al., 2008b).

Other periodicities however, like the 88-year Gleissberg cycle, have only been found for a few millennia.

W/S/M correspond to the Wolff, Spörer, and Maunder minima. a) Lomb-Scargle spectrogram on C solar activity reconstruction data grouped in 2000-yr windows, showing the distribution of spectral power for the 50-125 year range. This explains why the cycle cannot be detected in the sunspot record.

The 208-year de Vries solar cycle As previously described (see The 2400-year Bray Cycle), the de Vries solar cycle is strongly modulated by the Bray solar cycle.

The Eddy lows that correspond to this periodicity (orange bars) are numbered from most recent. Notice that the Bray periodicity is continuous over the entire Holocene, while the Eddy periodicity is very strong in the early Holocene and very weak in the mid-to-late Holocene. The Eddy lows that correspond to this periodicity (orange bars) are numbered from most recent. Yet the biggest group of researchers just call any periodicity between 50 and 150 years the Gleissberg cycle, often giving the name simultaneously to two different bands. Of interest to us here is only the ~ 88-year periodicity present in cosmogenic records that we can also call the Gleissberg cycle, if only to avoid further confusion.

Grand solar minima that correspond to these lows are indicated with boxes with their names. Joan Feynman, sister of the famous physicist, has studied the centennial solar cycle under the Gleissberg flag of convenience (Feynman & Ruzmaikin, 2014). The ~ 88-year Gleissberg cycle during the Holocene. The problem is that wavelet analysis shows that this periodicity was only apparent between 6,500 and 3,500 BP (figure 86).

Of the 25 GSM identified by Usoskin (2017) during the Holocene, only three are not located close to the lows of the Eddy or Bray cycles.

b) The spectral power distribution calculated for a 2000-yr window centered at 2,225 BP. Whether it is a real cycle subject to a very long modulation, or a temporal pseudo-periodicity that emerged from the unknown interactions that generate long term solar variability, cannot be determined.

Wavelet analysis shows the ~ 1000-year periodicity having a strong signal between 11,500 and 4,000 yr BP, and between 2,000 and 0 yr BP, but a very low signal between 4,000 and 2,000 yr BP (figure 79; Ma 2007; Kern et al., 2012). Several authors have noticed this solar forcing dominance during the early Holocene (figure 41; Debret et al., 2007; Simonneau et al., 2014). b) Holocene record of North Atlantic iceberg activity determined by the presence of drift-ice petrological tracers. When the amplitude of the 1000-year solar signal is adjusted by its wavelet power (figure 81), a high correlation between North Atlantic iceberg activity and the 980-year Eddy solar cycle corresponds to the periods when the 1000-year solar signal is high, while the correlation is low at periods of weak 1000-year solar signal, strengthening the relationship between climatic Bond events and solar activity, that has been acknowledged by multiple authors, starting with Gerald Bond himself (Bond et al., 2001). Black curve, a 1000-year frequency cycle representing solar activity for that periodicity, whose amplitude reflects the relative power (colored bar) of that frequency in a solar activity reconstruction wavelet analysis. Two of these GSM, at 10,165 and 5,275 years BP, also coincide with the Eddy cycle, as both cycles tend to coincide in phase when two Bray cycles (4,950 years), and five Eddy cycles (4,900 years) have passed. The name refers in some cases to a GSM cluster (cl.). As originally described, the Gleissberg cycle is unacceptable by modern scientific standards (and I would dare to say inexistent), and due to it the term Gleissberg cycle means different things to different authors.