wAbstract
@Milankovitch -climate theory provides a fundamental framework
for the study of ancient climates. Although the identification
and quantification of orbital rhythms are commonplace in paleoclimate
research, criticisms have been advanced that dispute the importance
of an astronomical climate driver. If these criticisms are valid,
major revisions in our understanding of the climate system and
past climates are required. Resolution of this issue is hindered
by numerous factors that challenge accurate quantification of
orbital cyclicity in paleoclimate archives. In this study, we
delineate sources of noise that distort the primary orbital signal
in proxy climate records, and utilize this template in tandem
with advanced spectral methods to quantify Milankovitch-forced/paced
climate variability in a temperature proxy record from the Vostok
ice core (Vimeux and others, 2002). Our analysis indicates that
Vostok temperature variance is almost equally apportioned between
three components: the precession and obliquity periods (28),
a periodic g100,000h year cycle (41), and the background continuum
(31). A range of analyses accounting for various frequency bands
of interest, and potential bias introduced by the gsaw-toothh
shape of the glacial/interglacial cycle, establish that precession
and obliquity periods account for between 25 percent to 41 percent
of the variance in the 1/10 kyr - 1/100 kyr band, and between
39 percent to 66 percent of the variance in the 1/10 kyr - 1/64
kyr band. These results are approximately two to four times greater
than those published by Wunsch (2004) for the same Vostok time
series. In all cases, most of the remaining variance is accounted
for by the g100,000h year cycle, which is distinct from a background
continuum that resembles autoregressive gred noise.h Our analysis
highlights the importance of a comprehensive assessment of the
climate signals in geologic records, and underscores the significance
of orbital forcing/pacing as a primary agent of Pleistocene climate
change.x
Introduction
The pathway of the orbital signal
Signal analysis methods
The Vostok temperature record
Quantification of orbital signals in the Vostok temperature record
Influence of the glacial/interglacial gsaw-toothh
Discussion
Conclusions
Acknowledgments
References