The 11 - year averaging period minimizes the effect of variability due to the 10 — 12 year periodicity of solar irradiance as well as irregular El Niño / La Niña warming / cooling in the tropical Pacific Ocean. (journals.plos.org)
Over time the 60 year periodicity essentially zeroes out. (realclimate.org)
Amongst the well - known proxies that have revealed a millennial - scale climate variability during the Holocene, the ice - rafted debris (IRD) indices in the North Atlantic developed by Bond et al. (1997, 2001) present a cyclicity of 1470 ± 500 years, which matches the 1228 ± 327 - year periodicity evidenced in the Mar Menor, considering the respective uncertainties in the periodicities. (kaltesonne.de)