Abstract
The main cycles of Earth's eccentricity as recorded in paleoclimate archives signify 2nd order terms, combining two g-frequencies associated with the precession of perihelia of the inner planets and Jupiter. However, many weaker cycles are present and may be documented as well. Here we report on a thus far unnoticed ~200-kyr cycle observed in rhythmically bedded marine marls and limestones of early Paleocene age in NE Spain and adjacent France. This cycle is expressed as alternating distinct and less distinct ~100-kyr CaCO3 maxima and associated magnetic susceptibility (MS) minima, which correspond to successive minima of the short ~100-kyr eccentricity cycle. The most plausible explanation is that this ~200-kyr cycle represents a weak but real cycle in eccentricity. Due to its weakness, this cycle is only expressed as alternatingly strong and weak ~100-kyr minima in eccentricity time series, a pattern that is identical to what we observe in the proxy records and outcrop. Its origin as eccentricity cycle is complex as it is composed of 4 to 6 individual components. A simplified solution solely based on the five leading g-frequencies reveals that most of these components originate from combinations of these 5 frequencies. However, they do not correspond to 2nd order terms, which underlie the principal short and long eccentricity cycles, but to much weaker higher order terms. Three of them have been identified as 4th order terms and two as 6th order terms, representing combinations of 2nd order terms, such as the first harmonic, 2(g2 – g5), of the 405-kyr cycle and related components. It is for the first time that the combined effect of such weak components has been identified in paleoclimatic records, which is only possible because they are not overwhelmed by much stronger 2nd order terms in this frequency band. Finally, the typical pattern that results from interference with the much stronger ~100-kyr cycle might be used as a template for testing the accuracy of astronomical solutions in the future.
Highlights
The astronomical theory of climate change starts from the notion that insolation received at the top of Earth's atmosphere varies in har mony with quasi-periodic changes in Earth's orbital and inclinational parameters, namely eccentricity with principal periods of ~100- and 405-kyr, axial inclination or obliquity with a dominant period of 41-kyr and climatic precession with main periods of 19- and 23-kyr
These cycles are primarily caused by gravitational perturbations by the pla nets and the Moon (e.g., Milankovitch, 1941) and the multitude of their components is connected with three fundamental frequencies, two of which are loosely connected with the planets, namely the g- and sfrequencies, which describe the precessional motions of their perihelia (g) and nodes (s), and astronomical precession, which is associated with the EarthMoon system (Laskar et al, 2004; Hinnov, 2000)
We argue that the cycle exemplifies a real but weak eccentricity component that is related to higher 4th and 6th order terms in eccentricity, which are much weaker than the 2nd terms that underlie the main cycles, such as the long 405-kyr and the short ~100-kyr eccentricity cycle
Summary
The astronomical theory of climate change starts from the notion that insolation received at the top of Earth's atmosphere varies in har mony with quasi-periodic changes in Earth's orbital and inclinational parameters, namely eccentricity with principal periods of ~100- and 405-kyr, axial inclination or obliquity with a dominant period of 41-kyr and climatic precession with main periods of 19- and 23-kyr These cycles are primarily caused by gravitational perturbations by the pla nets and the Moon (e.g., Milankovitch, 1941) and the multitude of their components is connected with three fundamental frequencies, two of which are loosely connected with the planets, namely the g- and sfrequencies, which describe the precessional motions of their perihelia (g) and nodes (s), and astronomical precession (with a frequency p termed the precession constant), which is associated with the EarthMoon system (Laskar et al, 2004; Hinnov, 2000). Cycles having a less familiar period close to ~200-
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