Ice Age Glacials, Milankovitch, Orbital Mechanics, and A Place For Dust?

I think we are all aware of Milankovitch and his cycles as an explanation of the Ice Age Glacials.

It fits pretty well, and I think on the “big lumps” it is most likely correct. There are some odd bits around the edges that don’t quite fit, though. Room to tune, for sure.

So I was reading this (rather well done) site on one of those “issues”:

In particular, this link from that aggregator page:

That, while very readable, goes into painful detail about exactly what we know about timings and exactly where they “have issues”. A sample:

Drysdale et al 2009

Variations in the intensity of high-latitude Northern Hemisphere summer insolation, driven largely by precession of the equinoxes, are widely thought to control the timing of Late Pleistocene glacial terminations. However, recently it has been suggested that changes in Earth’s obliquity may be a more important mechanism. We present a new speleothem-based North Atlantic marine chronology that shows that the penultimate glacial termination (Termination II) commenced 141,000 ± 2,500 years before the present, too early to be explained by Northern Hemisphere summer insolation but consistent with changes in Earth’s obliquity. Our record reveals that Terminations I and II are separated by three obliquity cycles and that they started at near-identical obliquity phases.

Standard stuff by now, for readers who have made it this far.

But the Drysdale paper is interesting on two fronts – their dating method and their “one result in a row” matching a theory with evidence (I extracted more text from the paper in note 5 for interested readers). Let’s look at the dating method first.

Basically what they did was match up the deep ocean cores that record global ice volume (but have no independent dating) with accurately radiometrically-dated speleothems (cave depositions). How did they do the match up? It’s complicated but relies on the match between the δ18O in both records. The approach of providing absolute dating for existing deep ocean cores will give very interesting results if it proves itself.

The correspondence between Corchia δ18O and Iberian-margin sea-surface temperatures (SSTs) through T-II (Fig. 2) is remarkable. Although the mechanisms that force speleothem δ18O variations are complex, we believe that Corchia δ18O is driven largely by variations in rainfall amount in response to changes in regional SSTs. Previous studies from Corchia show that speleothem δ18O is sensitive to past changes in North Atlantic circulation at both orbital and millennial time scales, with δ18O increasing during colder (glacial or stadial) phases and the reverse occurring during warmer (inter- glacial or interstadial) phases.

You get the idea. Pretty much goes through it all. The implication being that the insolation pattern alone is not sufficient and creates inconsistencies and incompatibilities with actual events.

So I took a look, again, at some old familiar friends / graphs / and all. I’ve seen again, something seen a dozen times+ and had a new thought (in the context of the above page). Here’s that standard graph:

Vostok Petit Ice Core showing Ice Age Pattern

Vostok Petit Ice Core showing Ice Age Pattern

OK, look at it for a minute. Temperatures get colder and colder. CO2 levels drop to plant starvation levels below 200 PPM (gee… never hear much about how nature cuts the CO2 down to near nothing in a glacial, do we…) and we are all very comfortable with that story. Gets cold, CO2 gets sucked down. Then “magic happens” and it gets warm enough to melt the ice and let the CO2 free ( 800 years later ) and good times return to the planet.

While waiting, it is fun to take a dividers (“compass”) and set the points the width of the last interglacial at the -2 line. Just about when the “plunge” gets going really fast. Then move those dividers over to “now”. My thought on that is that the Younger Dryas was an impact event that chopped the overshoot peak off of our interglacial. But now we are just about the same width as before from that -2 C point. Not much longer to go… Now back to the main line:

And we all ignore the dust.

At most it gets a bare mention as cold times being dry and dusty times.

I’m going to add what may be a new wrinkle.

So the speculation at SOD was that it was obliquity (axial tilt of the planet) cycles that set the pattern (though using variably 3 or 5 of them, and sometimes needing a ‘kicker’ from the other changes such as eccentricity). I’m going to point at dust. Yes, it rises over time. The world oh so slowly desiccates and dies. It takes time to dehydrate the soil and kill everything. Then grind it to a fine dust.

Eventually we have giant sand and dust storms that must be way bigger than the present ones from the Sahara. Sand and dust from there blows out into the Atlantic and eventually reaches Florida and the Caribbean in significant quantity. Yet during our present regime, we are “low dust” in the icy poles. There had to be much wider desert areas and much more dust in the wind to load the poles with dust.

My hypothesis is simply that “the dust matters”. During low obliquity, there isn’t enough sunshine to matter much. At the start of the process, there isn’t enough desert and blowing dust to move enough dust to the ice sheets. Only after enough life has died and enough soil is sand and dust, and we’ve gotten rid of all that dust trapping plant life between mid-latitudes and poles, only after enough ocean has gone to be icy poles exposing ever more mud flats globally and THEY dry; only then can enough dust be delivered onto those mid latitude ice sheets to make a significant albedo difference. At that point, the very next obliquity event can finally start that ice sheet melting. That, then, starts the positive feed back.

When this happens just before the right Milankovitch configuration, it can run to completion as an interglacial warm (and wet and living) period. When not so timed, it’s a ‘squib’ melt and fails to run to completion (like at about 60 MYBP where on the lower graph there is a spike of dust, but then life takes over and dust drops again, but without enough sun at 65 N to make it stick, and the glaciers return…)

I would also note that the dust peaks are getting larger over time. Artifact? Or is it getting ever harder to break the grip of ice…

In Conclusion

So that’s the idea. That it is a ‘3 way’ of obliquity, dust cycles, and Milankovitch as the gating event post initiation. That, then, lets Milankovitch drivers show up at the observed delay, while also helping to explain some of the “squib” events and why sometimes the sun is enough, and sometimes not.

Think of a very brown dry world and how it would respond to an obliquity kick in insolation. Then think about a wet green world. Then think about a very dry white ice world. Ice and cold can withstand the added sun. Green and wet can withstand the added sun (even if only the tropical belt and a bit into the temperate zones). But once “life dies and dries”, it’s a brown dusty land with brown dusty ice. That can’t stand the heat of more sun in the modest lattitudes when obliquity puts the sun right overhead.

So kick it around. See if it has legs, or is stuck in a sand trap ;-)

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About E.M.Smith

A technical managerial sort interested in things from Stonehenge to computer science. My present "hot buttons' are the mythology of Climate Change and ancient metrology; but things change...
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9 Responses to Ice Age Glacials, Milankovitch, Orbital Mechanics, and A Place For Dust?

  1. Graeme No.3 says:

    A reverse Reid Bryson? Well, he predicted cooling coming soon.

    Still, I think you have something. It is interesting that they now push the start of the previous interglacial back about 10,000 years. (That helps reduce the 10,000 year problem – see Wiki).
    It brings it more in line with what the geologists have been saying for the last quarter of a century (Devil’s Hole etc.) but increases the gap between the Eemian and the Holocene, so if the Eemian lasted 10,500 (as was claimed) then it cooled down around 130,000 BP, just allowing the Holocene to start around 20,000BP, just possible with Milankovitch.

  2. Larry Ledwick says:

    Might also be influenced by both the magnitude of the orbital eccentricity of the earth and the seasonal relationship between northern hemisphere summer, winter and perihelion (just one more minor kick event to encourage or damp a shift in mode from ice to green world.)

    This cycles within cycles stuff gets complicated.

  3. Seems we might need therefore to burn things that produce soot, so that the albedo of the ice changes. We’ve been trying hard to avoid that, of course, and get clean power. Could be that without that coal burning 60 years ago we might have flipped to a cold spell then.

    Just when you thought that those lignite mines could be retired in favour of nuclear fission, LENR or fusion, it looks like it might be an idea to just mothball the mines rather than shut them definitively. Rather than burning it, though, it’s maybe better to grind it and disperse it in the polar winds. That way it will last us longer, and we may need to use it for quite a while as the probability of a flip gets higher.

    The nice thing is that we’ve probably got at least 20 years to decide whether it’s going to be necessary. That’s probably long enough for even the most avid mainstream climate scientist to realise it’s getting colder despite what the IPCC says.

  4. Alan Poirier says:

    Earth is teetering on the edge of an ice age. It really wouldn’t take much to push us over — a nasty meteor impact, a few really big volcanic eruptions (they tend to increase during low solar cycles for whatever reason) and we’d start getting really cold winters like we’ve had in the past few years. Start losing a day of summer and gain a day of winter and before you know it you’ve got glaciers nipping at our heels (metaphorically speaking). I worry less about global warming than I do about global cooling. Let average temperatures drop 1 C and you can’t really grow wheat north of latitude 52N. Nasty business that.

  5. p.g.sharrow says:

    Those Great Ice Mountains covered with dust are the only way they could be melted, As long as they are white not enough insolation could be adsorbed to reduce them with winter cold and snowfall additions.
    It has struck me that the prairie that sustained the Mega fauna was in fact tundra like coverings of the dying Ice Mountains. Most areas of permafrost appear to be ice/snow covered with dirt and sand. Deposited and frozen in layers and not an existing deposit frozen in place. As long as there was Melting ice below the dirt soil covering it would be well watered during the summer and fall. A prime grazing land as long as it lasted and it would get better and larger with each passing year, until the ice ran out and the deposit dried.
    In most cases ice builds from the top down and melts from the bottom up. The dirt/dust would tip the conditions in favor of melt down of the surface over buildup from winter weather. pg

  6. Terry Jay says:

    The Washington State Palouse is said to be wind-blown loess originating in the channeled scablands of the Columbia River. Author John McPhee discusses great land-locked basins in Wyoming that could only have been excavated by wind. There must be other examples.

    In a glacial age, tornado, thunderstorm and such must have been common given the proximity of northern cold and tropical warm. A dry thunderstorm can ignite wildland fire, so add soot to the list.

  7. DocMartyn says:

    I never ignore the dust. Change your plot to -Log10[Dust] to show the three orders of magnitude change in dust levels between the ice/melt ages. Note also that changes in dust happen before either temperature or CO2.
    Increased dust also increases mineralization of oceanic carbon, so high dust=low [Co2] and low dust=high [CO2]

  8. Wayne Job says:

    Hi EM, your take on the dust and it’s role in the end of ice ages would certainly enhance and accelerate the end of glaciation. My take on the Milankovitch cycles is they are more an observation rather than the cause. Miles Mathis has it would seem a predictable cause of glaciation and interglacials using planetary mechanics and our alignment to the galactic core, strange man but oddly in the genius genus I liken him to Da Vinci.

  9. E.M.Smith says:

    @Terry Jay:

    Much of the midwest was classically called “The Great American Desert” and has huge deposits of wind blown dust and dirt. The “Dust Bowl” was not a unique event and will happen again.

    United States

    The Loess Hills of Iowa owe their fertility to the prairie topsoils built by 10,000 years of post-glacial accumulation of organic-rich humus as a consequence of a persistent grassland biome. When the valuable A-horizon topsoil is eroded or degraded, the underlying loess soil is infertile, and requires the addition of fertilizer in order to support agriculture.

    The loess along the Mississippi River near Vicksburg, Mississippi, consist of three layers. The Peoria Loess, Sicily Island Loess, and Crowley’s Ridge Loess accumulated at different periods of time during the Pleistocene.

    Ancient soils, called paleosols, have developed in the top of the Sicily Island Loess and Crowley’s Ridge Loess. The lowermost loess, the Crowley’s Ridge Loess, accumulated during the late Illinoian Stage. The middle loess, Sicily Island Loess, accumulated during early Wisconsin Stage. The uppermost loess, the Peoria Loess, in which the modern soil has developed, accumulated during the late Wisconsin Stage. Animal remains include terrestrial gastropods and mastodons.

    Loess soil forms sharp hills close to the Mississippi River and Yazoo River in western Mississippi north and south of Vicksburg. These deposits are more than 30 m thick (comparable to those in Iowa) immediately above the river valleys, to which they are sub-parallel, and thin to trace thickness within 40 km to the east. Streams and gulleys are incised very deeply and sharply between the linear loess ridges, making topography very important in the conduct of military operations for the Vicksburg Campaign.

    The Palouse Hills of eastern Washington and northern Idaho is a fertile agricultural region based on loess deposits.

    Glacial loess from the Matanuska Glacier blown into Matanuska Valley created the fertile soil conditions that motivated the Matanuska Colony resettlement experiment in Alaska during the Great Depression.

    Crowley’s Ridge in Arkansas is a natural loess accumulation point.

    Then there are the sand dunes:

    Colorado, New Mexico and (west) Texas each have one well-known dune-based park. The best, and one of the most magical places in the whole Southwest, is White Sands National Monument in New Mexico – 275 acres of pure white gypsum dunes, almost completely lacking in vegetation, sat in a wide, flat valley beneath the San Andres mountains. In Colorado, Great Sand Dunes National Park and Preserve features the tallest dunes in America, up to 700 feet high, with a rather incongruous location at the edge of the Rocky Mountains at elevation 7,500 feet. In Texas, Monahan Sandhills State Park contains a smaller area of golden dunes, still quite impressive, beside I-20 west of Odessa. Camping and sand-based recreation are the attractions for most visitors. Another Texas dune field is along the Gulf Coast, where Padre Island National Seashore protects a barrier island 80 miles long.

    Then add in that a lot of the prairie is on top of ancient sand dunes…

    The Sandhills, often written Sand Hills, is a region of mixed-grass prairie on grass-stabilized sand dunes in north-central Nebraska, covering just over one quarter of the state.

    I think that, taken together, the quantity of sand, loess and more all over the American Heartland speaks to a very large amount of wind blown sand and dust.

    So we’ve got loess all over the place and up to 30 m thick. That was a lot of blowing dust…


    OK, so “WE all” was a rhetorical device. I’d figured somebody might have inspected it, but wanted to “draw closer” with “we”. Oh Well.

    Per “ocean carbon” by which I presume you mean “ocean CO2”: I have an interesting chart of relative solubility of CO2 with temperature. Cold ice water absorbs about 2 x what warm water does. That cold world even without plants will suck down CO2 heavily. It would be interesting to do a “mineralization in ocean ice water rain stripping” experiment…

    @Wayne Job:

    I’ve looked at some of his stuff. It’s interesting, but often, IMHO, for the way his “leaps” are often “errors” that are hidden (ignored?) in interesting ways. Yes, a “top reading” of his often very dense stuff looks like genius (and in truth it is often hard to tell genius from ‘crazy talk’) but then there are the glaring errors. For example:

    Tries to claim calculus is all wrong and based on a “cheat”. As evidence, he says:

    The current and historical method for differentiating is a mess. In Lagrange’s derivation of the virial1, we find him differentiating x2 with respect to t, to find 2xdx/dt. He then lets dx/dt equal v, so that dx2/dt is equal to 2xv. I found this astonishing, but then was more astonished to find that it is done all the time, to this day. No one calls Lagrange on this cheat because they want to use it themselves. It is the same reason the Democrats never called the Republicans for stealing elections with voting machines. The Democrats wanted their turn with the machines, and got it.

    We could continue this cheat of Lagrange to find that 2xv = 2×2/t, which would mean that the derivative of x2 with respect to t is 2×2/t.

    Did you spot the slight of hand? It’s here: “the derivative of x2 with respect to t is 2×2/t. ”

    Going one way, the transform is from dx/dt (change of distance over change of time) as velocity (a definition, really) and extending it, he substitutes x/t and not dx/dt. That total distance over total time is not even known in this problem. How far and for how long does our object move? Thus he either has direct nonsense equations, or simply has failed to explain why this particular transform is reasonable and what circumstances make it so.

    He then wanders ever more into the swamp of imagination and even recognizes this issue:

    You will say, “C’mon, we all know that dx/dt is a velocity. What are you talking about? Velocity is defined as dx/dt, for heaven’s sake!” Yes, in many situations, it is. I am not denying that dx/dt is a velocity, as long as it is used correctly. What I am denying is that dx/dt in this particular case is equivalent to the definitional notation of velocity. I am pointing out something fundamental and of great importance, and you better open your eyes to it. The notation of calculus has always been convoluted and sloppy, and this sloppiness had already reached epidemic proportions by the time of Lagrange. If you differentiate x2, finding 2xdx/dt, the dx/dt in that notation is not a velocity. The notation is telling us that we are finding the rate of change of x2 with respect to the given rate of change of time. Since the given rate of change of time is always 1, dx/dt must also be one.

    So once recognizing that we are dealing with velocity, he says (in essence) “this time is different!”… then makes another “wopper leap”. Just how is it that ‘delta time’ or “rate of change of time” or how much time changes during our observation of movement is “always 1”? To me it looks like a cross connect failure between the passage rate of time being a constant at non-relativistic speeds and observational duration which is very non-constant.

    Frankly, I find his highly energetic wanderings with announcements of great import a bit tedious. He could use a lot less ego and a lot more fact checking and simple careful error analysis. In short, while clearly someone who thinks fast and about a lot, his is not a ‘tidy mind’…

    has a lot more such error combing, and I’d rather not get into it here.

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