Enlargement of figure 2 in order to highlight Milankovich cycles. All such
periods appear with a power about 100 times less than the 30 Myr's one.
A period (very strong: only 10 times less than the maximum power) at 20 Kyr
is present. Something like it (22 Kyr) has been found in GISP2 Lomb
periodogram as a medium-power spectral peak.
A low-power 23.8 Kyr peak is present and it could indicate the influence of
Precession is not so strong here.
Please note the vertical scale in figures 2 and 3.