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Author Topic: Milankovitch cycles  (Read 2105 times)

johnm33

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Milankovitch cycles
« on: January 07, 2015, 11:06:12 PM »
I keep seeing references to Milankovitch cycles which completely accept the theory, so this is just to air my scepticism without derailing elsewhere. In this, http://www.binaryresearchinstitute.org/bri/research/papers/ComparisonPaper.pdf , I find the better fit of angular momentum distribution particularly persuasive. In this, http://www.binaryresearchinstitute.org/bri/research/findingit/gravprobeb-update.shtml once again data which doesn't fit the paradigm is presumed compromised. When i have time i'll take a look for a link to my preferred theory.

Laurent

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Re: Milankovitch cycles
« Reply #1 on: October 18, 2015, 11:01:15 AM »
A paper in PNAS about possible an other Milankovitch cycle of 9millions years.

http://www.pnas.org/content/112/41/12604.abstract


Significance

The Milankovitch cycles are orbitally paced variations in insolation that drove periodic climate changes on Earth at the scale of tens to hundreds of thousands years. Longer ‟grand orbital cycles” also exist, but their impacts on paleoclimate dynamics are not well documented for pre-Cenozoic times. Here we tackle this issue by analyzing the stable isotope fluctuations recorded by fossil cephalopods throughout the Jurassic–Early Cretaceous interval. We document a periodicity of ∼9 My in the carbon cycle, except from 190 to 180 Ma when disturbances occurred. This orbital forcing affected carbon transfers by modulating the hydrological processes and sea-level changes. In summary, this ∼9-My orbital cycle is an important metronome of the greenhouse climate dynamics.


Abstract

Eccentricity, obliquity, and precession are cyclic parameters of the Earth’s orbit whose climatic implications have been widely demonstrated on recent and short time intervals. Amplitude modulations of these parameters on million-year time scales induce ‟grand orbital cycles,” but the behavior and the paleoenvironmental consequences of these cycles remain debated for the Mesozoic owing to the chaotic diffusion of the solar system in the past. Here, we test for these cycles from the Jurassic to the Early Cretaceous by analyzing new stable isotope datasets reflecting fluctuations in the carbon cycle and seawater temperatures. Our results document a prominent cyclicity of ∼9 My in the carbon cycle paced by changes in the seasonal dynamics of hydrological processes and long-term sea level fluctuations. These paleoenvironmental changes are linked to a great eccentricity cycle consistent with astronomical solutions. The orbital forcing signal was mainly amplified by cumulative sequestration of organic matter in the boreal wetlands under greenhouse conditions. Finally, we show that the ∼9-My cycle faded during the Pliensbachian, which could either reflect major paleoenvironmental disturbances or a chaotic transition affecting this cycle.
« Last Edit: October 18, 2015, 11:06:30 AM by Laurent »