622
Period g g g
[kyr] '? ! I
o
" I
.r:; II)
U Gl
:~":.;:
> "0
0 ·..:.:"U
c: 0
ro O \:
=Gl
::::!;Q.
,...;:
: 1
~ .~~
!; ",1:
~ i~
~ ~~
,
ct:>. ~ :
D :>
~
20
10
0
-10
iii' 20
~
0
Gl
"iii -20
u
en
u
'E
E
iii
Cl
0
....J
von Dobeneck and Schmieder
:! ~ N
~
I
:
I
I
o 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0 . 11 0.12 0.13 0.14 0.15 0.16
Frequency [1/kyr]
Fig. 13. Reference spectra (Blackman-Harris taper, WOSA: 3 segments) offundamental orbital frequencies and
their low-order (:;J) combinations based on astronomical time series (2500-0 ka; Berger and Loutre 1991). (Sub-)
Milankovitch periodicities (vertical dotted lines) are classified in groups (gray bars) of common order (index numbers) and origin (intermodulations (Int) and harmonics (Har)). Crosses depict 6dB bandwidths and 90 % confidence intervals. (a) A simple nonlinear transform of (b) the 65°N July insolation signal shows spectral characteristics in common with (b), (c) obliquity and (d) precession signal, even in the sub-Milankovitch 8- 18 kyrrange. Other
higher-order cycles of (a) coincide with (e) squared precession and (I) coupled obliquity and precession.