Please notice that this ice core is different with the previous two I analyzed: Crete and Dye3 This ice core has some information not explained by white noise. Unlike the previous two ice cores, which has no information significant than white noise. IMFs 3-6 have mean period: 14.86, 30.21, 60.82, and 182.68
The blue curve, i.e. sum of IMFs 3-6, seems have ~20 years cycle during 1800-present. Please see the next slide, the Fourier spectrum of IMFs 3-6.
It looks like there are one peak around 20-years. And also, there are some energy distribution around 50-year, too, if we use band-pass filter. I am sorry that I do not know how to test the statistics significance against the red background noise. My own method is based on EMD, which is quite complex.
Composite ice core (same as Chylek et al. 2011) I believe if we use some filters to remove the impacts of 20-year cycle, we could get this ~70-year cycle. As far as I can see, this can only exist in the composite time series, since this cycle is quite nonlinear (its spectrum is wide in any single core), the composite may give better represent.