Evaluating alternatives to the Milankovitch theory

Evaluating alternatives to the Milankovitch theory

Author links open overlay panelStephen J.Puetza
AndreasProkophbGlennBorchardtc
https://doi.org/10.1016/j.jspi.2015.10.006
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Highlights

•Orbital tuning removes spectral power from non-Milankovitch frequencies.
•Orbital tuning inhibits testing of alternatives to the Milankovitch theory.
•Reporting bias occurs by publishing positive results while hiding negative results.
•Spectral analysis of orbitally tuned time-series involves circular reasoning.
•Choices about how to orbitally tune records also results in altered cyclicity.

Abstract

The physical process that causes cycles in Earth’s precession, obliquity, and eccentricity is well established, and researchers have detected and modeled the orbital cycles for millions of years into the past. The Milankovitch theory postulates that Earth’s orbital cycles contribute to similar periodicity in climatic variation — with the periods of the climatic cycles primarily ranging from 19,000 years to 1,200,000 years. Even while support for the Milankovitch Theory remains strong, opposition to the process of tuning sedimentary records to Milankovitch models has become increasingly vocal. Here, we discuss another negative aspect of orbital tuning that has been ignored to this point. Specifically, orbital tuning contributes to a type of negative analytical bias against research aimed at modifying the Milankovitch theory as well as bias against testing alternatives to the Milankovitch theory, such as the Universal cycle model, presented in this work.

https://doi.org/10.1016/j.jspi.2015.10.006

NASA's recently updated take:

https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/
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FEATURES | February 27, 2020
Milankovitch (Orbital) Cycles and Their Role in Earth's Climate
By Alan Buis,
NASA's Jet Propulsion Laboratory

Our lives literally revolve around cycles: series of events that are repeated regularly in the same order. There are hundreds of different types of cycles in our world and in the universe. Some are natural, such as the change of the seasons, annual animal migrations or the circadian rhythms that govern our sleep patterns. Others are human-produced, like growing and harvesting crops, musical rhythms or economic cycles.

Cycles also play key roles in Earth’s short-term weather and long-term climate. A century ago, Serbian scientist Milutin Milankovitch hypothesized the long-term, collective effects of changes in Earth’s position relative to the Sun are a strong driver of Earth’s long-term climate, and are responsible for triggering the beginning and end of glaciation periods (Ice Ages).

Specifically, he examined how variations in three types of Earth orbital movements affect how much solar radiation (known as insolation) reaches the top of Earth’s atmosphere as well as where the insolation reaches. These cyclical orbital movements, which became known as the Milankovitch cycles, cause variations of up to 25 percent in the amount of incoming insolation at Earth’s mid-latitudes (the areas of our planet located between about 30 and 60 degrees north and south of the equator).

The Milankovitch cycles include:

-The shape of Earth’s orbit, known as eccentricity;
-The angle Earth’s axis is tilted with respect to Earth’s orbital plane, known as obliquity; and
-The direction Earth’s axis of rotation is pointed, known as precession.

Let’s take a look at each (further reading on why Milankovitch cycles can't explain Earth's current warming here).

Eccentricity – Earth’s annual pilgrimage around the Sun isn’t perfectly circular, but it’s pretty close. Over time, the pull of gravity from our solar system’s two largest gas giant planets, Jupiter and Saturn, causes the shape of Earth’s orbit to vary from nearly circular to slightly elliptical. Eccentricity measures how much the shape of Earth’s orbit departs from a perfect circle. These variations affect the distance between Earth and the Sun.

Eccentricity is the reason why our seasons are slightly different lengths, with summers in the Northern Hemisphere currently about 4.5 days longer than winters, and springs about three days longer than autumns. As eccentricity decreases, the length of our seasons gradually evens out.

The difference in the distance between Earth’s closest approach to the Sun (known as perihelion), which occurs on or about January 3 each year, and its farthest departure from the Sun (known as aphelion) on or about July 4, is currently about 5.1 million kilometers (about 3.2 million miles), a variation of 3.4 percent. That means each January, about 6.8 percent more incoming solar radiation reaches Earth than it does each July.

When Earth’s orbit is at its most elliptic, about 23 percent more incoming solar radiation reaches Earth at our planet’s closest approach to the Sun each year than does at its farthest departure from the Sun. Currently, Earth’s eccentricity is near its least elliptic (most circular) and is very slowly decreasing, in a cycle that spans about 100,000 years.

The total change in global annual insolation due to the eccentricity cycle is very small. Because variations in Earth’s eccentricity are fairly small, they’re a relatively minor factor in annual seasonal climate variations.

obliquity with border
Credit: NASA/JPL-Caltech

Obliquity – The angle Earth’s axis of rotation is tilted as it travels around the Sun is known as obliquity. Obliquity is why Earth has seasons. Over the last million years, it has varied between 22.1 and 24.5 degrees perpendicular to Earth’s orbital plane. The greater Earth’s axial tilt angle, the more extreme our seasons are, as each hemisphere receives more solar radiation during its summer, when the hemisphere is tilted toward the Sun, and less during winter, when it is tilted away. Larger tilt angles favor periods of deglaciation (the melting and retreat of glaciers and ice sheets). These effects aren’t uniform globally -- higher latitudes receive a larger change in total solar radiation than areas closer to the equator.

Earth’s axis is currently tilted 23.4 degrees, or about half way between its extremes, and this angle is very slowly decreasing in a cycle that spans about 41,000 years. It was last at its maximum tilt about 10,700 years ago and will reach its minimum tilt about 9,800 years from now. As obliquity decreases, it gradually helps make our seasons milder, resulting in increasingly warmer winters, and cooler summers that gradually, over time, allow snow and ice at high latitudes to build up into large ice sheets. As ice cover increases, it reflects more of the Sun’s energy back into space, promoting even further cooling.

precession with border
Credit: NASA/JPL-Caltech

Precession – As Earth rotates, it wobbles slightly upon its axis, like a slightly off-center spinning toy top. This wobble is due to tidal forces caused by the gravitational influences of the Sun and Moon that cause Earth to bulge at the equator, affecting its rotation. The trend in the direction of this wobble relative to the fixed positions of stars is known as axial precession. The cycle of axial precession spans about 25,771.5 years.

Axial precession makes seasonal contrasts more extreme in one hemisphere and less extreme in the other. Currently perihelion occurs during winter in the Northern Hemisphere and in summer in the Southern Hemisphere. This makes Southern Hemisphere summers hotter and moderates Northern Hemisphere seasonal variations. But in about 13,000 years, axial precession will cause these conditions to flip, with the Northern Hemisphere seeing more extremes in solar radiation and the Southern Hemisphere experiencing more moderate seasonal variations.

Axial precession also gradually changes the timing of the seasons, causing them to begin earlier over time, and gradually changes which star Earth’s axis points to at the North Pole (the North Star). Today Earth’s North Stars are Polaris and Polaris Australis, but a couple of thousand years ago, they were Kochab and Pherkad.

There’s also apsidal precession. Not only does Earth’s axis wobble, but Earth’s entire orbital ellipse also wobbles irregularly, primarily due to its interactions with Jupiter and Saturn. The cycle of apsidal precession spans about 112,000 years. Apsidal precession changes the orientation of Earth’s orbit relative to the elliptical plane.

The combined effects of axial and apsidal precession result in an overall precession cycle spanning about 23,000 years on average.

A Climate Time Machine

The small changes set in motion by Milankovitch cycles operate separately and together to influence Earth’s climate over very long timespans, leading to larger changes in our climate over tens of thousands to hundreds of thousands of years. Milankovitch combined the cycles to create a comprehensive mathematical model for calculating differences in solar radiation at various Earth latitudes along with corresponding surface temperatures. The model is sort of like a climate time machine: it can be run backward and forward to examine past and future climate conditions.

Milankovitch assumed changes in radiation at some latitudes and in some seasons are more important than others to the growth and retreat of ice sheets. In addition, it was his belief that obliquity was the most important of the three cycles for climate, because it affects the amount of insolation in Earth’s northern high-latitude regions during summer (the relative role of precession versus obliquity is still a matter of scientific study).

He calculated that Ice Ages occur approximately every 41,000 years. Subsequent research confirms that they did occur at 41,000-year intervals between one and three million years ago. But about 800,000 years ago, the cycle of Ice Ages lengthened to 100,000 years, matching Earth’s eccentricity cycle. While various theories have been proposed to explain this transition, scientists do not yet have a clear answer.

Milankovitch’s work was supported by other researchers of his time, and he authored numerous publications on his hypothesis. But it wasn’t until about 10 years after his death in 1958 that the global science community began to take serious notice of his theory. In 1976, a study in the journal Science by Hays et al. using deep-sea sediment cores found that Milankovitch cycles correspond with periods of major climate change over the past 450,000 years, with Ice Ages occurring when Earth was undergoing different stages of orbital variation.

Several other projects and studies have also upheld the validity of Milankovitch’s work, including research using data from ice cores in Greenland and Antarctica that has provided strong evidence of Milankovitch cycles going back many hundreds of thousands of years. In addition, his work has been embraced by the National Research Council of the U.S. National Academy of Sciences.

Huge ice age methane blowout is ill omen for glacier retreat
Earth 1 June 2017

By Andy Coghlan
The massive craters were formed around 12,000 years ago, but are still seeping methane and other gases

The massive craters still seep methane

Andreia Plaza Faverola/CAGE

Call it the largest fart in Earth’s history. As the most recent ice age came to a close 12,000 years ago, retreating glaciers in the Barents Sea north of Norway triggered unprecedented blowouts of methane gas from massive dome-like features on the seabed.

Methane leaking from the permafrost today tends to be released very gradually or absorbed into vegetation or seawater. But evidence of the prehistoric blowouts, from dome structures on the seabed called pingos, suggests much larger and more rapid releases are possible.

With glaciers in Antarctica and Greenland retreating fast because of global warming, the big worry is that there could be pingos hiding underneath waiting to “go pop” in the same way, says Karin Andreassen at the Centre for Arctic Gas Hydrate, Environment and Climate at the Arctic University of Norway.

CERN and Mont Blanc: Explore particle physics and glaciers in Switzerland on a New Scientist Discovery Tour

Andreassen and her colleagues pieced together the story using detailed seismic and geologic data of the Barents seabed captured through high-resolution echo sounding from ships. They also looked at the composition of methane-containing gases still spewing up from the remains of 100 pingos.

Old methane

Analysis of the gas profiles revealed that the methane originated 30,000 years ago from hot zones of hydrocarbon-containing rock about a kilometre below the seabed. At that time, thick layers of ice over the seabed kept any methane that percolated upwards trapped in the uppermost layer of sediment down to depths of around 400 metres. Inside the sediment, the gas was converted into a solid ice-like mixture called a gas hydrate.

Then, 17,000 to 15,000 years ago, the ice sheet began to retreat rapidly, reducing the overhead pressure and causing hydrates to decompose. As they broke down, they released methane gas – the solid and stable gas hydrate layer became thinner and weaker. The pressure of the gas was strong enough to push up the seafloor to form pingo domes as much as a kilometre across.

By 12,000 years ago, the ice sheets had melted and the pingos were covered by an influx of warmer seawater from the Atlantic Ocean instead of ice. This made the hydrate layer so thin – just 30 metres – that the pingos could no longer withstand the pressure from below. The pingos burst, releasing the powerful greenhouse gas into the atmosphere, a process that probably took a few weeks per pingo.

The risks of something similar happening today are hard to predict, says Andreassen. The distribution of pingos on the seabed isn’t well charted elsewhere in the world. “We don’t have much seafloor data on pingo formation offshore of contemporary ice sheets like Antarctica and Greenland,” she says. But both regions are reckoned to be sitting on rich reserves of hydrocarbons.

Ice interplay

“Increased warming would increase the risk of releasing gas from gas hydrate pingos,” she says. But it would depend on the interplay of ice sheets, gas hydrates and permafrost in each area, as well as the capacity for gas to percolate upwards from much deeper hydrocarbon reserves. “It seems very unlikely that gas would be released from many areas simultaneously,” she says.

Other researchers are equally sanguine. “Unless a glacier happens to cap a deep thermogenic [hydrocarbon] source, the lack of any carbon would preclude the formation of massive shallow hydrates,” says Patrick Crill at Stockholm University in Sweden. “So I’m not too worried.”

Crill also points to previous research suggesting that over the past 800,000 years – including eight ice ages – atmospheric methane levels have varied between 350 and 700 parts per billion, much less than today’s 1900 parts per billion.

“There are spikes in the data, but they never exceed 700ppb, and to my mind, that represents all the inputs into the natural system prior to the Anthropocene,” he says.

In other words, the blowouts 12,000 years ago might have been large, but they appear to have had little impact on global methane levels at the time, which still fell well short of today’s levels.

Journal reference: Science, DOI: 10.1126/science.aal4500

Read more: https://www.newscientist.com/article/2133397-huge-ice-age-methane-blowout-is-ill-omen-for-glacier-retreat/#ixzz6LdORFUCz

Miles' Charge Field and the Sun cycles are primary:
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How Often Do Ice Ages Happen?

By Laura Geggel - Associate Editor March 25, 2017

The last ice age led to the rise of the woolly mammoth and the vast expansion of glaciers, but it's just one of many that have chilled Earth throughout the planet's 4.5-billion-year history.

So, how often do ice ages happen, and when is the next freeze expected to begin?

The answer to the first question depends on whether you're talking about big ice ages or the little ice ages that happen within those larger periods. Earth has undergone five big ice ages, some of which lasted for hundreds of millions of years. In fact, Earth is in a big ice age now, which explains why the planet has polar ice caps. [Photo Gallery: Antarctica's Pine Island Glacier Cracks]

Big ice ages account for about 25 percent of Earth's past billion years, said Michael Sandstrom, a doctoral student in paleoclimate at Columbia University in New York City.

The five major ice ages in the paleo record include the Huronian glaciation (2.4 billion to 2.1 billion years ago), the Cryogenian glaciation (720 million to 635 million years ago), the Andean-Saharan glaciation (450 million to 420 million years ago), the Late Paleozoic ice age (335 million to 260 million years ago) and the Quaternary glaciation (2.7 million years ago to present).

These large ice ages can have smaller ice ages (called glacials) and warmer periods (called interglacials) within them. During the beginning of the Quaternary glaciation, from about 2.7 million to 1 million years ago, these cold glacial periods occurred every 41,000 years. However, during the last 800,000 years, huge glacial sheets have appeared less frequently — about every 100,000 years, Sandstrom said.

This is how the 100,000-year cycle works: Ice sheets grow for about 90,000 years and then take about 10,000 years to collapse during warmer periods. Then, the process repeats itself.

Given that the last ice age ended about 11,700 years ago, isn't it time for Earth to get icy again?

"We should be heading into another ice age right now," Sandstrom told Live Science. But two factors related to Earth's orbit that influence the formation of glacials and interglacials are off. "That, coupled with the fact that we pump so much carbon dioxide into the atmosphere [means] we're probably not going to enter a glacial for at least 100,000 years," he said.

What causes a glacial?

A hypothesis put forth by the Serbian astronomer Milutin Milankovitch (also spelled Milanković) explains why Earth cycles in and out of glacials and interglacials.

As the planet circles the sun, three factors affect how much sunlight it gets: its tilt (which ranges from 24.5 degrees to 22.1 degrees on a 41,000-year cycle); its eccentricity (the changing shape of its orbit around the sun, which ranges from a near-circle to an oval-like shape); and its wobble (one full wobble, which looks like a slowly spinning top, happens every 19,000 to 23,000 years), according to Milankovitch.

In 1976, a landmark paper in the journal Science provided evidence that these three orbital parameters explained the planet's glacial cycles, Sandstrom said.

"Milankovitch's theory is that the orbital cycles have been predictable and very consistent throughout time," Sandstrom said. "If you are in an ice age, then you'll have more or less ice depending on these orbital cycles. But if the Earth is too warm, they basically won't do anything, at least in terms of growing ice." [Doomsday: 9 Real Ways Earth Could End]

One thing that can warm Earth is a gas such as carbon dioxide. Over the past 800,000 years, carbon dioxide levels have fluctuated between about 170 parts per million and 280 ppm (meaning that out of 1 million air molecules, 280 of them are carbon dioxide molecules). That's a difference of only about 100 ppm between glacials and interglacials, Sandstrom said.

But carbon dioxide levels are much higher today when compared with these past fluctuations. In May 2016, Antarctica carbon dioxide levels hit the high level of 400 ppm, according to Climate Central.

Earth has been warm before. For instance, it was much warmer during the dinosaur age. "[But] the scary thing is how much carbon dioxide we've put in [the atmosphere] in such a short period of time," Sandstrom said.

The warming effects of that carbon dioxide will have big consequences, he said, because even a small increase in Earth's average temperature can lead to drastic changes, he said. For instance, Earth was only about 9 degrees Fahrenheit (5 degrees Celsius) colder, on average, during the last ice age than it is today, Sandstrom said.

If global warming causes both Greenland's and Antarctica's ice sheets to melt, the oceans will rise about 196 feet (60 meters) higher than they are now, Sandstrom said.

What leads to big ice ages?

The factors that caused the long ice ages, such as the Quaternary glaciation, are less well-understood than those that led to glacials, Sandstrom noted. But one idea is that a massive drop in carbon dioxide levels can lead to lower temperatures, he said.

For instance, according to the uplift-weathering hypothesis, as plate tectonics pushed up mountain ranges, new rock became exposed. This unprotected rock was easily weathered and broken apart, and would fall into the oceans, taking carbon dioxide with it.

These rocks provided critical components that marine organisms used to build their calcium-carbonate shells. Over time, both the rocks and the shells took carbon dioxide out of the atmosphere, which, along with other forces, helped lower carbon dioxide levels in the atmosphere, Sandstrom said.

More at link:  https://www.livescience.com/58407-how-often-do-ice-ages-happen.html

https://en.wikipedia.org/wiki/Milankovitch_cycles



Past and future Milankovitch cycles via VSOP model
• Graphic shows variations in five orbital elements:
Axial tilt or obliquity (ε).
Eccentricity (e).
Longitude of perihelion ( sin(ϖ) ).
Precession index ( e sin(ϖ) )
• Precession index and obliquity control insolation at each latitude:
Daily-average insolation at top of atmosphere on summer solstice ({\displaystyle {\overline {Q}}^{\mathrm {day} }}{\displaystyle {\overline {Q}}^{\mathrm {day} }}) at 65° N
• Ocean sediment & Antarctic ice strata record ancient sea levels & temperatures:
Benthic forams (57 widespread locations)
Vostok ice core (Antarctica)
• Vertical gray line shows present (2000 A.D.)

Springerplus. 2015; 4: 285.
Published online 2015 Jun 20. doi: 10.1186/s40064-015-0942-6
PMCID: PMC4506281
PMID: 26203405

The Sun-Earth connect 3: lessons from the periodicities of deep time influencing sea-level change and marine extinctions in the geological record

Robert GV Baker
corresponding author and Peter G Flood
Author information Article notes Copyright and License information Disclaimer

Abstract

A number of papers since Rampino and Stothers published in Science 1984 have reported common periodicities in a wide range of climate, geomagnetic, tectonic and biological proxies, including marine extinctions. Single taper and multitaper spectral analysis of marine fluctuations between the Late Cretaceous and the Miocene replicates a number of the published harmonics. Whereas these common periodicities have been argued to have a galactic origin, this paper presents an alternative fractal model based on large scale fluctuations of the magnetic field of the Sun. The fluctuations follow a self-similar matrix of periodicities and the solutions of the differential equation allow for models to be constructed predicting extreme events for solar emissions. A comparison to major Phanerozoic extinction, climate and geomagnetic events, captured in the geological record, show a striking loop symmetry summarised in major 66 Ma irradiance and electromagnetic pulses from the Sun.

Keywords: Periodicity, Geological record, Solar model, Self-similarity

Introduction

The proposition that human emissions of greenhouse gases (GHGs), especially carbon dioxide, has and will continue to produce warming of the globe and accelerating sea-levels is the current paradigm. The claim is that anthropogenic input of GHGs is so large that we can assign the term “Anthropocene” Epoch for the present because it is dominated by human-induced effects. The predictions are accepted unequivocally with the end result being that climate change is the defining issue of today.

However, Anthropogenic Global Warming (AGW) should also be considered in the context of the geological record of climate change and its proxies, such as sea-level fluctuations, for it is now accepted that during the past two billion years the Earth’s climate has fluctuated between “Icehouse” (Cold) periods and “Greenhouse” (Hot) periods. For example, Miller et al. (2008) describe the largest global cooling event of the Cenozoic (33.8 and 33.5 Ma ago), where the Earth’s climate switched from warm, high CO2 conditions, to variable “Icehouse” climates where icesheets grew to be 25% larger than present. There was a corresponding ~67 m eustatic sea-level decrease and there was a 21% extinction of taxa in the geological record (Sepkoski 2002). Such fluctuations have been argued not to be random but periodic. Raup and Sepkoski (1984) analysed ~3,500 families of marine animals (vertebrate, invertebrate and protozoan) and concluded that there was significant periodicity in 12 extinction events with a 26 Ma mean interval. More recently, Rohde and Muller (2005) using Fourier Spectral Analysis (FSA), identified a strong periodicity of 62 ± 3 Ma in the cyclicity of marine diversity through the Phanerozoic, based on an analysis of Sepkoski (2002) compendium. Lieberman and Melott (2012), using the Paleobiology Data Base (PBDB), undertook spectral analysis of this data base, which also showed a strong spectral peak of 63 Ma. With such periodicities a recurring result in data analysis, further discussions have eventuated on the origin of this periodicity, focusing on the position or motion of the Sun moving through the Milky Way (Lieberman and Melott, 2012).

Smith and McGowan (2005) have contested the biological implications of this periodicity, arguing that the fossil record mirrors the rock outcrop area and that the cyclicity comes from sampling rather than biological signals. However, Omerbashich (2006) used Gauss-Vanicek spectral analysis of the Rohde and Muller (2005) data, removed all zero values and still found significant periodicities at 140.23 Ma and 91.30 Ma at 99%; and 110.3 Ma, 66.85 Ma and 32.12 Ma at 95% confidence levels. Melott (2008) undertook power spectrum analysis using Lomb-Scargle methods and found significant periodicities of 99.9% at 63.1 ± 6 Ma and 46 Ma and argued that the 62 Ma periodicity appears in two largely independently generated data sets with multiple methods of analysis (Table 1). This periodicity has been further re-analysed and examined by Lieberman and Melott (2012) using the PBDB, which again showed a strong peak of 63 Ma with the spectral peaks differing by only 1.6 Ma. They conclude that there is a strong signal within paleobiological data bases of 62 ± 3 Ma and 31 ± 1 Ma and a specific extinction metric of 27 ± 1 Ma, despite criticisms of individual data bases, analytical methods and problems of sampling from the fossil record.


Rampino and Stothers (1984) summarise the spectral peaks of five Phanerozoic time series (impact craters, tectonic episodes, carbonatite intrusions, kimberlite intrusions and geomagnetic reversals; Table 1). There were common periodicities of 12 Ma, 16 Ma, 20-23 Ma and 32-35 Ma. Further, Rampino & Stothers (1984) analysed the periodicity in Vail et al. (1977) Exxon sea-level data and found two periodicities in the spectrum of residuals of ~21 Ma and ~33 Ma. Likewise, analysis of major discontinuities of sea-floor spreading produced periodicities of 18 Ma, 23 Ma and 34 Ma. Active tectonism on the continents also correlates with episodes of lower sea-levels. They also analysed pulse phases of 18 principal Phanerozoic orogenic phases revealing spectral peak clusters of 20 Ma and 31 Ma to 33 Ma, 36 Ma, 44 Ma, 61 Ma, 81 Ma and 270 Ma. Geomagnetic reversals follow similar periodicities (Table 1). What could have produced the concurrence in these cycles? Rampino & Stothers (1984) conclude various external forcing mechanisms such as collisions with comets and asteroids as the likely cause with crater periodicities of 12 Ma, 16 Ma, 32 Ma and 260 Ma, but there still needs to be an underlying periodic mechanism to account for such correlations, such as, between orogenic events and biological extinctions. The key question remains in the understanding of the dynamics within the geological record: why do such a plethora of proxies produce such common periodicities?

Sea-level change in the Phanerozoic


Sea levels are the manifestation of the sum totals of climate change parameters including forcing and feedback factors. At present values of 460 ppm C02-equivalent, the Earth’s climate is tracking towards the upper stability limit of the Antarctic ice sheet which is defined at 500 ppm and 4°C warmer than present. The resulting melting would raise sea levels by 4-6 m (as was the case in the last Pleistocene interglacial 126,000 yr BP). Above this level of 500 ppm, the Earth would track from its current Icehouse conditions back to Greenhouse Earth conditions, such as, during the mid-Eocene 40 Ma ago with the consequences of substantial sea-level shifts and fundamental climate change.

Research during the past four decades has established certain relationships between sea level, ice volumes, temperature and carbon dioxide (Miller et al. 2005; Haq and Schutter 2008). The global or eustatic sea-level changes are principally controlled by two variables, namely, the volume of water in the oceans, and the volume of ocean basins. The Earth’s sea-level record for the past 540 Ma has been summarised by Hallam (1984) and Haq et al. (1987). The publication of the record by Vail et al. (1977) and Haq et al. (1987), including sea-level histories, which in industry circles is referred to as the Exxon Production Research (EPR) record, represents a major achievement in Earth Sciences (Figure 1). Most of periodicities observed in spectral analysis of sea levels and sea-floor spreading again show similar periodicities to Table 1 of between 18-23 Ma and 33-34 Ma (Rampino & Stothers, 1984) suggesting complex climatic-tectonic interdependence.

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Figure 1

The Exxon Sea-level Curve with E, H and W solar phase boundaries (see Figure 4). W-peaks are warm period maximums from the intense irradiance of an active Sun, where E-points and H-points are the beginning and end boundaries for the passive phases of the Sun. H-phases relate to glacial periods and lowstands in Phanerozoic sea levels, whereas W-phases relate to high sea surface temperatures and highstands in sea level.

Spectral analysis of sea-level fluctuations

Sea-level fluctuations can now be analysed by sophisticated spectral analysis using a recent detailed data from the Late Cretaceous to Miocene (108–9.7 Ma) (Kominz et al. 2008). Two methods of analysis will be used; firstly, a single taper Blackman (Harris) spectral analysis to discern longer cycles in the record and secondly, multitaper spectral analysis (Thomson, 1982) using five tapers (K = 5) and a bandwidth (BW = 4) to deconstruct any shorter cycles within the data set. Multitaper methods render power spectrum analysis using Lomb-Scargle single taper methods, such as in Melott (2008) as only, at best, first order approximations.

Spectral methods, such as, the Lomb-Scargle algorithms, over-emphasise data points at the centre and weakly weights extreme values. The Blackman tapers can apply 20% cosine weightings (or tapers) to address this problem and discards only 12.5% of available data variable constraints. This taper may be adequate in many cases but would not be appropriate for dispersive or unusually band-limited signals (Park et al. 1987). It can, however, analyse unevenly partitioned data: a common feature of climate and geological proxies. The Multitaper spectral method was developed by Thomson (1982) to overcome the trade-off between the resistance to spectral leakage and the variance of the spectral estimates from single taper algorithms. It discards very little data and weights the data relatively evenly with significance determined by an F-Ratio and therefore is quite sophisticated (Park et al. 1987). The data partitioning over time, however, must be evenly spaced.

The Blackman (Harris) algorithm was undertaken on the Kominz et al. (2008) evenly partitioned data set using Autosignal ‘Blackman-Harris 4’ (BH4) with a cosine taper, whilst the multitaper analysis (BW = 4 and K = 5) used Autosignal for ‘Fourier Multitaper Spectra’. The data samples are every 100 ka meaning that both methods were appropriate. The significant periodicities are listed in Table 2. The Blackman (Harris) BW4 algorithm produced significant periodicities at 143.55 Ma and 31.16 Ma at 99% and 17.07 Ma at 95%. The Multitaper analysis, where significant F-values (95%) must be coincident with spectral peaks (dB), yielded shorter periods of 724,482; 1,040,736; 2,059,639; and 4,886,962 yrs (Table 2). The increased number tapers deconstruct the longer periods from BW4 and are less useful to compare with the summary results in Table 1. The sea-level periodicities therefore share common signals of 16 ± 1 Ma and 34 ± 2 Ma and 140 Ma (half the 275 ± 10 Ma) with periodicities in marine diversity, tectonic episodes, intrusions and geomagnetic reversals. Sea-level change is therefore also part of this synchronicity.
Table 2

Spectral Analysis of the Kominz et al. 2008 data on sea-level fluctuations from 9.7 to 108Ma (at ** 99%; * 95% and 90% significance)
Blackman (Harris) BH4 Multitaper BW = 4 K= 5 Theoretical loop (L), loop & tail (LT) and loop & double tail (L2T) periods
Frequency Power Period (Ma) Frequency dB F-value Period (yr) Solar Harmonics R3 (fast) Solar Harmonics R5 (slow)
0.00698 133.35** 143.55 1.38030 50.11 8.996** 724,482 718,336 NA
L
0.03209 18.80** 31.16 1.43889 47.90 8.790* 694,978
0.05860 10.51* 17.07 0.96081 52.19 8.154* 1,040,786 1,077,504 1,029,971
L2T LT
1.82489 45.92 7.002* 547,977
0.48552 55.04 6.393* 2,059,639 2,155,008 2,060,000
L2T LT
0.63620 46.51 5.099* 1,571,830
3.25914 46.22 4.832* 306,829
0.20462 58.86 4.730* 4,886,962 4,310,016 4,944,000
L2T LT
3.45539 47.74 4.372 289,403
1.22590 51.23 4.306 815,729 NA 823,858 L
46.51 4.207 1,478,860 1.436,672 L 1,648,000 L
45.71 4.193 536,760 538,752 514,997
L2T LT

Spectral analysis of marine stratigraphic variability

The tectonic episodes follow the same periodicity as the other proxies. Recent research by Myers and Peters (2011) of stratigraphic variability in North America during the Phanerozoic using Multitaper Spectral Analysis confirms this with a strong periodicity of 56 ± 3 Ma. This is concurrent with the ~50 Ma periodicity in magmatic activity in the Sierra Nevada batholith. They argue that this timing is consistent with other oscillatory proxies and its tempo is statistically similar to known rhythms in a number of marine animal genera in the global fossil record. Meyers and Peters further demonstrate that there is a eustatic contribution where marine strata in North America exhibits 55 Ma oscillations.

What is the origin of this periodicity?

Extra-terrestrial sources have been suggested to explain the periodicity, where Raup & Sepkoski (1984) propose that the path of the Sun through the spiral arms of the Milky Way, affects the cosmic ray intensity reaching the Earth. Shaviv (2003) analysed 50 iron meteorites and deduced that there was a 143 Ma periodicity in the cosmic ray intensity, which is one of the frequencies of marine diversity and sea-level fluctuation in the spectral analyses. More recent hypotheses are summarised by Lieberman and Melott (2012) who look at possible origins from the motion of the Sun within The Milky Way with a 200 Ma approximate period from a wobble of the Sun in transit, coinciding with a vertical oscillation of 63 Ma. Whilst such explanations are possible, they are still not convincing, since they do not explain the appearance of equally justifiable and possibly related sub-harmonics in the spectral analysis. The key question remains: why do such a plethora of proxies produce such common periodicities?

Another major external source could be concurrent large-scale periodic fluctuations in the Sun’s magnetic field and irradiance affecting the Earth’s geomagnetic field and climate systems. Such extreme fluctuations could involve in-phase flipping between the latitudinal and longitudinal twisting in the Sun’s toroidal and meridinal magnetic fields. The flipping would depend on the Sun’s core rotational speed and whilst sunspot formation occurs latitudinally at present, other stars, such as, AB Doradus or EK Dranconis, have starspots forming along meridians of longitude and the poles are a convergence of sunspot formation (Figure 2). This flipping mechanism could ensure long term relative stability in irradiance output within a chaotic system of thermonuclear production (Baker 2014). Such flipping behaviour in the Sun’s dynamo in the core and the changing location of field-line emissions and solar flare production could synchronously affect ionization of the Earth’s atmosphere, impacting on global temperatures, particularly at the poles. Further, the Sun’s magnetic field switching through a cycle of situations could underpin the Earth’s geomagnetic field reversals, producing fundamental shifts in convective currents and plume locations in the mantle, and in the transitional phases, increasing the incidence and severity of UV radiation and galactic cosmic ray penetration to land and ocean surfaces. Such a source could explain the coincidence in periodicities, if they could be shown to follow the same long-term periodicities within a pulsating Sun.
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Figure 2

A computer simulation of the star AB Doradus where the starspots form along meridians of longitude and the polar zones are regions of sunspot and solar flare maximums. Does the Sun flip to such magnetic field structures during higher rotational phases and extremes of thermonuclear production, synchronously affecting the Earth’s geomagnetic field and atmospheric ionisation? (Source: Cameron A., Jardine M., Wood K.,University of St Andrews)

If the Sun’s magnetic field flipping coincides with the geomagnetic reversals on Earth, there is little geomagnetic field protection during the switching process of between 5000–10,000 yr and the Earth will concurrently receive high UV-B emissions and galactic cosmic ray incursions during these transitions between field flipping and rotation of the solar dynamo within thermonuclear production. The effect of UV-B radiation of phytoplankton production rates is significant (Larsen, 2005), so such saturation would have the ability to significantly disrupt marine food webs as well as terrestrial species. This would also be a time of high galactic cosmic ray incursions and atmospheric ionization. If there were concurrent changes to the Sun’s gravitational pull on the solar system, it would not be surprising that impact crater periodicities could be largely synchronous with geomagnetic reversals, sea-level fluctuations and marine extinctions (Table 1).

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4506281/

Earth’s rock record preserves evidence of numerous natural processes, from evolution and extinction to catastrophes and climate change, and sometimes even planetary configurations.

In a new study, a well-preserved sequence of Triassic lake sediments bearing evidence of cyclical patterns of climate change in the Newark Basin confirms the existence of a Milankovitch cycle — a periodic change in the shape of Earth’s orbit caused by, in this case, Earth’s gravitational interactions with Jupiter and Venus. The finding can be used to precisely date other events in the geological record, and inform climate and astronomical models.

Geologists previously suggested the patterns found in the Newark Basin, an ancient rift basin covering northern New Jersey, southeastern Pennsylvania and southern New York, could reflect the climatic effects of a predicted 405,000-year Milankovitch cycle, but the Newark Basin sediments were unable to be dated precisely enough to confirm the link.

Other Milankovitch cycles — a 23,000-year cycle related to the wobble of Earth’s axis, a 41,000-year cycle related to the tilt of the axis, and a 100,000-year cycle related to orbital eccentricity — are relatively well established based on glaciological and sedimentary records. Such astronomical cycles influence how much solar energy the planet receives and thus alters climate, for example by producing wet and dry periods, which leave their mark in the rock record.

Petrified Forest National Park Rock Cores Confirm Milankovitch cycleRocks from Arizona’s Petrified Forest National Park helped scientists identify signals of a hypothesized Milankovitch cycle, a regular variation in Earth’s orbit, that appears to have influenced the planet's climate as far back as the Triassic Period. Credit: Kevin Krajick/Lamont-Doherty Earth Observatory
In the study, published in Proceedings of the National Academy of Sciences, geologist Dennis Kent of Columbia University’s Lamont-Doherty Earth Observatory and Rutgers University and colleagues assigned dates to the Newark Basin rock record by correlating it with rocks cored from the Upper Triassic Chinle Formation in Petrified Forest National Park in Arizona. Uranium-lead dating of zircons found in volcanic ash layers produced precise ages for the Arizona rocks, which the team then correlated to the Newark Basin rocks by matching the pattern of Earth’s magnetic field reversals recorded in both places. The key is that “the Newark core has the [climatic] cycles. The Arizona core has the dates,” Kent says.

The researchers found that the dates of the climate cycles recorded in the Newark Basin rock record match the 405,000-year cycle predicted by astronomical models, providing the first empirical evidence for the cycle’s existence and stability over the last 215 million years.

“This is the first time we can actually confirm the theoretical description of the 405,000-year cycle,” says geologist Linda Hinnov of George Mason University, who was not involved in the study. “The astronomers have given us this model but we’ve never been able to establish that it’s actually accurate until now.”

However, a concern raised by Spencer Lucas, curator of paleontology at the New Mexico Museum of Natural History and Science, is that while the Newark record was deposited in an ancient lake, the Arizona sequence was deposited by a river, which makes it more likely to have gaps in the magnetic field history it records. “If you want a complete record of magnetic polarity, you have to have a complete pile of sediments. If you don’t have that, then you’re not going to get a complete record,” Lucas says.

Such gaps are to be expected and they are small compared to the overall length of time recorded in the section, which suggests that the overall pattern of magnetic field reversals is still likely to have been recorded accurately, says co-author Paul Olsen, a paleontologist at Columbia University’s Lamont-Doherty Earth Observatory. Also, the gaps do not affect the precision of the zircon dating, he adds.

Confirming the existence of the steady, regular astronomical cycle that has been operating in the same way for more than 200 million years provides astronomers reconstructing the history of the solar system with a predictable marker, much like the beat of a metronome, to calibrate their models.

Current astronomical models apply the laws of Newtonian dynamics and general relativity to reconstruct the solar system’s past configurations, but model predictions fail beyond about 50 million years. That’s because it is difficult to predict the motion of more than two moving bodies in space over very long periods of time. Astronomers are limited to computing the positions of the planets incrementally, and at each increment, errors accumulate.

“In addition, the physics of the solar system is chaotic,” Olsen says, meaning that modern astronomical models are highly sensitive to initial conditions, and therefore, the picture of planetary positions hundreds of millions of years ago can vary widely depending on the initial assumptions and conditions input to a model.

However, because astronomers know the configuration of Earth, Venus and Jupiter when the 405,000-year cycle is at its minimum and maximum, and because those events are evident in the rock record and have now been well-dated, astronomers have more solid data on which to base estimates of planetary configurations going back more than 200 million years.

The discovery represents a linchpin in a hypothesis that Olsen and his colleagues have been developing for decades called the “Geological Orrery,” after the 18th-century mechanical models of the solar system. It holds that climatic change recorded in the geologic record could be used to infer the former positions and motion of planets in the solar system going back hundreds of millions of years.

More at link: https://www.earthmagazine.org/article/geologic-evidence-confirms-existence-405000-year-milankovitch-cycle