Guest Post by Dan Johnston
I have been following the proposed collision theory for the onset of the Younger Dryas for a number of years with considerable interest as it explains so much in a relatively straightforward fashion, if true. The academic response to the hypothesis has been, predictably, harsh and unforgiving with accusations flying back and forth as to procedures and interpretations. I did, however, enjoy one researcherās claim that he could not reproduce the results reported in one peer-reviewed paper on the evidence for an impact. The impact researchers countered with the valid observation that the scornful researcher did not bother to use the same time-consuming methods they employed to extract extremely small microtectite spherules and nanodiamonds from sediments.
Carl Saganās āExtraordinary claims require extraordinary evidenceā comes to mind with regard to the Younger Dryas claims but I have to admit, based on the global warming āconsensus,ā that this fundamental principle of science seems to have been trumped by politics and media attention in the past. I do remember the long struggle involved in getting the Alvarezās theory of a catastrophic asteroid impact causing the end of the Cretaceous and extinction of the dinosaurs accepted. No matter how much physical evidence was gathered from around the world, acceptance (a much stronger word to me than consensus) didnāt happen until the smoking gun of the Cretaceous impact was located at Chicxulub in the Yucatan. Once the crater had been found, resistance to the asteroid theory rapidly crumbled and it is generally accepted as fact by most scientists today, though there is still a small minority of ādeniers.ā
The Chicxulub impact was a relatively straightforward exercise in science compared to the extraordinary claims being made about the cause of the Younger Dryas. WUWT has been following the Younger Dryas debate closely for a number of years and I wonāt belabor the background information on its evolution except to say that resistance to the idea seems overwhelming despite repeated attempts to present more extensive, rigorous and compelling evidence. Just as with the end of the dinosaurs the extinction of mammoths and other North American megafauna requires an air-tight case and this will only happen when a crater or other irrefutable evidence of an impact is discovered and, preferably, dated.
When confronted with the fiery question of where evidence lies of an impact that only occurred some 12,800 years ago, barely time for a deep breath geologically, the Younger Dryas Impact proponents respond with an extremely weak mumbling about āair blasts,ā asteroid clusters and ice sheet impacts that left no evidence of a large chunk(s) of space debris hitting the Earth. They point out that the Tunguska Impact (called an impact even though it left no crater) was an air-blast at an altitude of 3-6 miles (5-10 km) above Siberia that yielded the equivalent of 3-30 megatons of TNT in explosive force. The skeptics counter with Meteor Crater in Arizona, a beautiful little 1,200 ft (4,000 m) diameter hole 570 ft (170 m) deep made by a meteorite a mere 54 yds (50 m) in diameter that released 10 megatons of energy upon impact. They reasonably expect that a piece or pieces of space debris able to spread ejecta over half of the northern hemisphere, cause a 1,300 year halt in global warming and lead to the extinction of numerous species that had survived for hundreds of thousands of years had to leave some evidence of its arrival behind. The YD proponents then countered with the fact that the northern half of North America was covered with ice sheets and an impact on a 1 to 2 mile thick layer of ice may have mitigated the expected formation of a crater.
An impact on an ice sheet does seem reasonable as the evidence from the ongoing investigation points at the impact occurring somewhere in north-central North America near what is now the Great Lakes. Unfortunately, there is no crater evident and the projected impact should have left some imprint on the earth, even if it was a cluster of meteorites or an airburst. Letās take the researchers at their word and look where the evidence points-the Great Lakes.
Water is capable of hiding almost everything beneath its waves but bathymetric maps showing the depths to lakebed of the Great Lakes can give us some idea of what lies beneath. A number of years ago, I looked at bathymetric maps of the Great Lakes because I was curious about alarmists reports of the five Great Lakes drying up due to global warming. I didnāt see any reason for alarm for the foreseeable future but did note what I considered an anomaly in the map for Lake Michigan in the central part of the southern lake. The map can be viewed at http://www.glerl.noaa.gov/data/bathy/ and is shown below.
Figure 1 Bathymetry of Lake Michigan (Great Lakes Environmental Research Laboratory)
The almost circular feature has a diameter of almost 40 miles (64.5 km) and the topography seems to indicate relatively steep slopes down to a central depression. A higher resolution view of the anomaly is shown in Figure 2 and comes from the Great Lakes Rescue Project at http://www.ngdc.noaa.gov/mgg/greatlakes/lakemich_cdrom/html/images.htm .
Figure 2 High Resolution Bathymetry of Southern Lake Michigan (GLRP)
I am not a geologist but this image definitely suggests the possibility of an impact crater, probably modulated by a considerable thickness of ice lying above the point of impact. A quick check of the assumed conditions at the proposed onset of the Younger Dryas (12900-12800 YBP) shows that at this time Lake Chicago existed as a melt lake with an outlet near Chicago and covered the southernmost tip of the current Lake Michigan. At this time, just north of Lake Chicago, the Michigan Lobe of the Wisconsin Glaciation was in rapid retreat. There is no reason to dismiss the likelihood that the edge of the ice sheet may have lain to the south of the Southern Chippewa Basin (SCB), the location of the anomalous terrain. After the onset of the Younger Dryas, the glacial front advanced for a millennium before the retreat resumed.
A check of the underlying geological explanation for the formation of the SCB is classical geological speculation with no real data. The belief is that easily eroded Devonian shale overlay a more resistant Silurian dolomite (the same or a similar formation to the one that forms Niagara Falls). The glacial front scooped out this almost circular feature by differentially eroding the shale while in doing so leaving behind steep escarpment walls into the basin and a shallow plateau just to the north. The story seems somewhat weak to me and, as far as I can tell, no samples of what lies beneath have ever been obtained from the SCB. I really feel it would be a wonderful idea to find out just what happened to form the SCB.
The Younger Dryas Impact proponents would be well-served by promoting an exploration of the SCB as a starting point while looking for other anomalies further north in the deeper Chippewa Basin and in other Great Lakes. If a smoking gun does exist for their theory, it probably lies under these waters.
As a footnote, an impact with the ice sheet and its catastrophic effects could explain the other primary explanation of the source for the Younger Dryas. An asteroid strike leaving one or more craters in the Great Lakes area could have resulted in a rush of fresh water flowing either north into the Arctic or out the St Lawrence Seaway and shutting down the North Atlantic conveyor transporting heat from the equator. Thus, the two theories would merge into a progressive explanation of the sudden cooling, its long duration and the deaths of the megafauna.
One of the main problems is that the isotope signature, ie d18O, dD AND deuterium excess, and accummulation rates of the Greenland ice cores during the Younger Dryas are identical to the Dansgaard Oescher events. http://en.wikipedia.org/wiki/Dansgaard%E2%80%93Oeschger_event
Therefore one should wonder why the Younger Dryas needed an impact and 25 similar events did not.
“Meteor Crater in Arizona, a beautiful little 1,200 ft (4,000 m) diameter hole 570 ft (170 m) deep….”
Methinks the 1200 ft should be meters, & the 4000 m should be feet….?
Offtopic.
I believe, everybody MUST read this:
http://www.welt.de/debatte/henryk-m-broder/article116332834/Eine-Behoerde-erklaert-die-Klimadebatte-fuer-beendet.html
German Ecology Ministry claims any “climate debate” as finished and publishes a list of persons who deny climate change.
According to the Ministry, these persons should not publish anything in official newspapers.
Did not expect such things were possible 70 years after Nazi Germany.
[Best to post this into the “Tips and Notes” thread.
Note: The new (just anointed (er, appointed) US Dept of Energy king (er, head) ALSO said equivalent statements in his coronation speech in front of his adoring audience of DOE serfs (er, employees) and lackeys. Mod]
“When confronted with the fiery question of where evidence lies of an impact that only occurred some 12,800 years ago, barely time for a deep breath geologically, the Younger Dryas Impact proponents respond with an extremely weak mumbling about āair blasts,ā asteroid clusters and ice sheet impacts that left no evidence of a large chunk(s) of space debris hitting the Earth.”
No, they do not respond with an extremely weak mumbling regarding to what happened, instead, they have this to say:
http://wattsupwiththat.com/2012/06/13/new-evidence-of-younger-dryas-extraterrestrial-impact/
Have you thought much about the profile? The South Chippewa Basin, although fairly circular, has very even slopes all the way to a central deepest point–not typical. The northern ‘basin’ is twice as deep and very precipitous outer sides even if it is not circular. Dunno.
I must say that “āExtraordinary claims require extraordinary evidenceā is drivel. What extraordinary evidence did Einstein’s claims need for support? One astronomical observation that may anyway not have been precise enough to do the job. What extraordinary evidence did Clerk-Maxwell’s field theory, or Planck’s quantum notion, need? Come to that, Newton’s claims about gravitation, the greatest advance in the history of physics, needed no new evidence to persuade people: it just cast a fresh and compelling light on heaps of old evidence.
A large stony meteorite, as opposed to the much rarer metallic sort, exploding in the atmosphere above 1-2 kms of ice, would leave no sign of impact, but there should be dust/ash/something in the ice core records.
“I must say that āāExtraordinary claims require extraordinary evidenceā is drivel. What extraordinary evidence did Einsteinās claims need for support? One astronomical observation that may anyway not have been precise enough to do the job. ”
This is utter nonsense. It’s not like Einstein came up with an outlandish idea, and as soon as the first confirmation came in, everybody took his good word for it ever since. – Of course Einstein has been put to the test in many, many experiments and observations and a hundred years on, it has been confirmed time and time again with very high precision. – Actually extraordinary claims DO require extraordinay evidence, which is precisely why Einstein is being put to the test up to this day. you have a distorted understanding of what is going on š
Have to say that the South Chippewa Basin looks like a pretty normal depression. Worthwhile someone having a dig, but I wouldn’t be holding my breath (I’d use SCUBA gear…).
On the more general point of asteroid/comet or not as the cause of the YD, our ancient texts/drawings/carvings might point towards the former. Ancient civilisations the world over, from China, India, the Middle East, Europe, Africa and the Americas, feature dragons as the bringers of disaster. Firebreathers with long, fiery tales coming from the sky. If you start from the premise that they weren’t real creatures, the best explanation for the ‘dragon’ featuring across the world is that they were meteors of some description. There’s some (though not compelling) evidence dating many of these civilisations to at least 10-12K years ago. I wouldn’t say that this means “Yes, an impact caused the YD”, but it seems to me more likely than not that some fireballs from the skies scared the bejesus out of our ancestors so much that the legend was depicted for millennia afterwards. Exactly when this event or these events occurred is another matter.
It certainly merits having an open mind to the impact hypothesis, rather than writing it off completely. We might not find The Crater, but the evidence is building.
70% of the Younger Dryas cooling occurred in less than a decade. The abrupt cooling is the reason for the extinction. The magnitude and rapidity of the cooling is unimaginable. The regions of the planet affected, cool from interglacial warm to glacial cold with 70% of the cooling occurring in less than a decade. There is for example 15C cooling on the Greenland Ice sheet during the 1300 interval of cooling. Britain had a year average temperature of 5C during this cold interval compared to its current average temperature of 13.5C.
There are cycles of abrupt cooling captured in the Greenland Ice sheet record. When the planet cools there is an increase in desertification and an increase in zonal winds. There is a 10 fold increase in dust from the Sahara desert that is deposited on the Greenland Ice sheet during these cyclic abrupt climate change cooling intervals. The increase in dust in the Greenland ice sheet cores is a signature of this special cyclic event.
The duration of the Younger Dryas abrupt cooling period is 1300 years. Extraterrestrial impacts are not capable of cooling the planet for 1300 years.
The cooling due to a comet or a meteoroid impact is similar to a large volcanic eruption. The duration of cooling for that type of forcing mechanism is less than a decade. Insolation at N65 was at maximum for the duration of the Younger Dryas abrupt cooling interval. A very power forcing mechanism is required to cause the cyclic abrupt cooling.
The analysis indicates the Younger Dryas burn marks have been heated to a temperature in excess of 2200 C at 18 different locations at different latitudes and longitudes on two different continents.
That would require 12 to 18 separate extraterrestrial objects. It is physically impossible for a single object to breakup and cause the observed pattern of burn marks due to the distribution of the burn marks on the planet.
The Younger Dryas researchers have not involved astrophysicists when they formulated the impact hypothesis to explain the burn marks. An astrophysicist would unequivocally rule out extraterrestrial objects as the cause of the burn marks. PBS had a special on the Younger Dryas Impact theory and interviewed an astrophysicist who made that statement. It is astonishing that the researchers did not include astrophysical analysis (orbital paths and so on) as part of their hypothesis analysis.
It is unlikely to the point of being close to physically impossible for there to be 12 to 18 separate naturally occurring extraterrestrial objects all of the goldilocks size to heat the planet to greater than 2200C at the locations, without leaving impacts marks, as based on the locations of the burn marks on the planetās surface, would require that multiple objects with different orbital paths have struck the earth.
Impacts on the earth of the objects of the goldilocks size are very, very, rare. Multiple independent source bodies all striking the earth within a few years, is not a viable explanation for the burn marks.
The Younger Dryas abrupt cooling was caused by an abrupt geomagnetic excursion. There are cycles of geomagnetic excursions. There is a geomagnetic excursion, the Gothenburg geomagnetic excursion that is dated to have occurred at the same time as the Younger Dryas. There are other geomagnetic excursions at other abrupt cooling periods. The special type of Dansgaard-Oeschger cycle cooling ā the very, very rapid extreme cooling that sometimes follows the D-O warming phase, is called a Heinrich event. Geomagnetic excursions have been found at the termination of past interglacial periods.
http://en.wikipedia.org/wiki/Younger_Dryas
http://www.sciencedirect.com/science/article/pii/003358947790031X
The Gothenburg Magnetic Excursion
http://sciences.blogs.liberation.fr/home/files/Courtillot07EPSL.pdf
http://www.vvkuz.ru/books/Kuznetsov_and_Kuznetsova.pdf
The Earth Palaeoclimate Response to Cosmic Rays Exposure During Geomagnetic Field Excursions
http://earthobservatory.nasa.gov/Newsroom/view.php?id=24476
Glacial Records Depict Ice Age Climate (William: abrupt cooling periods) In Synch Worldwide
Is the geodynamo process intrinsically unstable?
http://eprints.whiterose.ac.uk/416/
Most holes in the ground tend to end up as circular. Its the way of nature. Turn an hour-glass upside-down and see what happens. Subduction can and will do the same.
.
Another problem is when exactly did then the Younger Dryas start? There are two main ideas. 12.7 and 12.9 thousand kalendar years ago. There is some convincing evidence, duplicated in several independent counted records that it really was 12.7 If the impact was at 12,9 Ka then you’d have an synchronity problem to begin with.
@William Howard Astley
William, The Gothenburg geomagnetic flip was an artifac and has never been reproduced. You won’t find any contemporary publication referring to it. There has never been retractions or refutals, but It’s not there, anywhere. The rumor has it that the sediment core was broken and put together again the wrong way.
This guy (see link) put together a pretty comprehensive hypothesis on the same subject. He proposes multiple impacts and air-blasts from a broken up comet. I haven’t read the entire post yet, but what I have read so far seems pretty interesting.
http://cometstorm.wordpress.com/2011/04/27/a-different-kind-of-climate-catastrophe-2/
I have read that some are not convinced that the meteor strike at Yucatan was not responsible for the dinosaurs extinction primarily because of the lack of fossils found in the KT boundary. If it had wiped them out, shouldn’t there be a lot of fossils at that level? Just shows that what is settled may not be.
errr, *was* responsible – ack, need coffee,…
William Astley said:
“There are cycles of abrupt cooling captured in the Greenland Ice sheet record. When the planet cools there is an increase in desertification and an increase in zonal winds. There is a 10 fold increase in dust from the Sahara desert that is deposited on the Greenland Ice sheet during these cyclic abrupt climate change cooling intervals. The increase in dust in the Greenland ice sheet cores is a signature of this special cyclic event.”
Should that be an increase in meridional rather than zonal winds during a cooling phase ?
One would need more meridional winds to carry more dust from North Africa to Greenland.
If so, that would accord with my general hypothesis and that we are currently in a more meridional and slightly cooling regime than we were when the sun was more active.
Nastapoka Arc, Hudson Bay, could be also a serious candidate.
http://www.vukcevic.talktalk.net/NArc.htm
Distinct coincidence between magnetic and gravity anomalies indicates something extraordinary.
Impact was likely to be from a huge āironā meteorite, since slowly sinking into the crust, with sections of it reaching the Curie temperature of iron around 770 degrees C, judging by the decline in the magnetic intensity of the area.
leftturnandre says:
May 24, 2013 at 12:27 am
I agree with leftturnandre that the YD does not need to appeal to an atmospheric event, since other more plausible explanations exist. Several have been advanced here, such as the Dansgaard Oescher events as you propose. William Astley is no doubt correct that an impact cannot affect climate for a millenium. My own penny-worth theory is that the YD is just part of the “bipolar seesaw” of interhemispheric climate oscillation preceding the Holocene.
I have always felt that there is āno case to answerā with the Younger Dryas (YD). Glacial periods ā in contrast to interglacials such as (and especially) the Holocene, are characterised by rapid, even violent, climate temperature swings up and down, as William Astley again points out, in the context of which the YD is not very exceptional. (Glacial epochs are punctuated by “micro-interglacials” lasting less than a century.)
This view is reinforced even more by literature on the bipolar seesaw (reciprocal oscillation between north and south hemispheres) around the time of the YD and before, leading up to the Holocene. One of the most important such papers is Blunier et al 1997 who show that the YD was just the NH reacting to a warming southern ocean. It was proposed by Tzedakis et al 2012 that sharpened bipolar seesawing marked both the beginning and the end of interglacials. Thus in Blunier we see ā in fig. 2 ā first a warming in the southern ocean about 16 kYa, then the āAntarctic cold reversalā, a cooling oscillation in the SH, coinciding with sharp NH warming prior to the YD. Then a warming upswing in the SH ending the cold reversal coincides with the abrupt YD. It is noted by Barker et al 2009 that the seesaw is characterised by smooth sinusoidal oscillation in the SH but more abrupt changes in the NH, caused in the latter case by Atlantic meridional overturning circuation (AMOC) regime changes. Then at the Holocene inception both NH (abruptly) and the SH (smoothy) rise in temperature, but the SH again cools slightly in advance of the Holocene optimum.
One thing that is clear is how Jeremy Shakun, holder of the chair in climate fraud at Oregon SU, has shamelessly exploited the end-glacial bipolar seesaw to concoct a spurious proof of CO2 leading the temperature rise out of the last glacial. Southern ocean temperatures had been rising since 16 kYa and continued to rise during the YD, resulting in a small CO2 increase in anticipation of the Holocene, on the condition that you take the Holocene to begin after the YD. But CO2 was not driving the start of the Holocene, it was merely following the southern ocean established warming. (There is more ocean in the SH than NH.)
If we demand an atmospheric deus ex machina to explain every upward and downward wiggle of climate history we are falling into the trap of AGW believers, who are unable to accept any cause of temperature change other than atmospheric input by humans and are in denial of the existence of the worldās oceans.
Having been cursed with seeing a stony asteroid three times now by eye and in Earth’s atmosphere I think there are more important things to worry about than what caused the Younger Dryas. This one is >1.75 miles in diameter, mostly dark with some ruddy orange plasma and flickers. I call it “Itys” (Son of Tereus) for obvious reasons. YHBW.
Sorry – I forgot the links:
Blunier et al 1997
Tzedakis et al 2012
Barker et al 2009
There was also an Older Dryas event that started at 14,300 years ago where temperatures dropped by more than they did in the Younger event at 12,800 years ago.
The issue is the Greenland ice core scientists have never really been clear about the record. It’s all been about global warming scare for them, of which the Younger Dryas was just the one they focused on.
If an asteroid caused the event, then there were about 23 of them during the last ice age because that is how many rapid cooling events there were. More likely is that there are many periods of glacial advance from accumulation at central load points on the ice-sheets in the far north, interspersed with periods when the glaciers melted back just as rapidly. Even in the downturns of the Milankovitch Cycles, solar insolation at 65N was more than strong enough in the summer to melt the ice. The ice-sheets had no business getting down to Chicago and New York. The summer sun is too strong.
The megafauna were mostly mega-grass-herbivores (and then mega-carnivores that fed on them). When the ice age was ending, the extensive grassland habitat that covered most of North America because of low CO2 and low precipitation during the ice ages, was replaced with more C3 bushes and trees. There wasn’t enough grassland left for dozens of giant species.
And giant rivers from the melting ice which flowed south to the Gulf of Mexico would have cut them off into small regions where local extinction became more likely. An entire herd could be wiped out by simply trying to ford one of these rivers in the summer. A few mega species survived, most didn’t.
William Astley says:
May 24, 2013 at 2:17 am
I would be grateful for your comment on the following point quoted from Maslin et al 2001, concerning Dansgaard-Oeschger events with an apparent 1500 year period:
One cautionary note is that Wunsch has suggested a more radical explanation for the pervasive 1500-year cycle seen in both deep-sea and ice core, glacial and interglacial records. Wunsch suggests that the extremely narrow spectral lines (less than two bandwidths) that have been found at about 1500 years in many paleo-records may be due to aliasing. The 1500-year peak appears precisely at the period predicted for a simple alias of the seasonal cycle sampled inadequately (under the Nyquist criterion) at integer multiples of the common year. When Wunsch removes this peak from the Greenland ice core data and deep-sea spectral records, the climate variability appears as expected to be a continuum process in the millennial band. This work suggests that finding a cyclicity of 1500 years in a dataset may not represent the true periodicity of the
millennial-scale events. The Holocene Dansgaard-Oeschger events are quasi periodic, with different and possibly stochastic influences.
Note the author is not questioning the existence of the D-O events but calls them instead quasi-periodic, and suggests that the very regular 1500 year signal might be an aliasing artefact, not the real D-O events. The many posters here who regularly refer to the 1500 year periodic events needs to address this possibility.
I find this an interesting theory, off of Racine in Lake Michigan (directly west of that hole) there is an underwatwer structure locally known to fishermen as “the hills” three very distinct series of smooth rising/falling hills that rise and fall as you go several miles east into Lake Michigan directly towards that hole. Those hills are not as evident out of Kenosha (to the south) or Milwaukee (to the north). I just started fishing out there and was wondering what could carve out out those hills, Racine onhore is pretty flat, the Silurian rock of this area seems too hard to carve out like that. Perhaps those hills are some sort of remant of a collision, and there are other “hills” out there to find if one were to go more towards the middle of the lake then travel right towards that hole. Anyways something to ponder while trolling this summer, I metal detect the beaches of this area always on the lookout for fossils or ancient stuff including meteorites and have never found nor seen any evidence of a meteor collision.
Phlogiston et al,
I do believe that things are still quite a bit different. Maybe have a peek at this work in progress:
https://dl.dropboxusercontent.com/u/22026080/YD%20working%20paper.pdf
leftturnandre says:
May 24, 2013 at 5:52 am
Phlogiston et al,
I do believe that things are still quite a bit different. Maybe have a peek at this work in progress:
https://dl.dropboxusercontent.com/u/22026080/YD%20working%20paper.pdf
Whoa – that would put the cat among the pidgeons, if correct!
Where is the evidence for crater in the sediment stratigraphy?
http://deepblue.lib.umich.edu/bitstream/handle/2027.42/22932/0000498.pdf;jsessionid=2CD4117159AFA6B9E1CBD1645AFB99E0?sequence=1
Phlogiston,
scrutinize, try to shoot it down. That’s how science works isn’t it?
Don’t need a crater. Airbursts have already been observed. A meteor or comet “stream” will produce a multitude of airbursts, especially if it comes in at a shallow angle.
***
William Astley says:
May 24, 2013 at 2:17 am
***
Please stop the incessant magnetic cr*p.
regarding the KT boundary: “If it had wiped them out, shouldnāt there be a lot of fossils at that level? Just shows that what is settled may not be.”
Remember that fossilization requires some unique circumstances present, and that vast majority of organisms that have died on earth have left no fossils. Most importantly, a fossil needs almost instant sedimentation after death in order to be preserved from natural processes, which generally means shallow ocean bottoms or swampy areas (ie, the carboniferous period) A disaster as proposed at the KT boundary, which would have resulted in a mostly dead world, may not have produced the kind of conditions which would have led to fossils being quickly buried and preserved.
“The almost circular feature has a diameter of almost 40 miles (64.5 km) and the topography seems to indicate relatively steep slopes down to a central depression.”
Please. The key word there is “seems”. Just because there are a lot of contour lines does not mean that the slopes are steep. 150 m change in elevation over ~32 km radius? That does not equate to “relatively steep slopes”. That is equivalent to a 4 m rise (or fall) per kilometer (about 5 inches per 100 feet) would be imperceptible to a person walking over the terrain. Even the steepest slope is approximately 70 m over 10 km (7 m over a kilometer; 8 inches over 100 feet).
You admit to not being a geologist, but wish to throw out hundreds of years of geologic investigations in the Lake Michigan area as speculation and replace it with your own speculation which requires that an ice lobe be in place over the SCB at the time instead of Lake Chicago so that you can further speculate on a meteor strike. Speculation heaped on speculation while dismissing all geologic evidence as speculation?
If that is a crater, it is both not very deep and not round enough. Craters tend to be very circular, and if the central depression is visible I’d expect more traces of the outer ring. Maybe sediment covered most of it. However, studying Great Lakes sediment is an obvious exercise, and has been going on for some time.
The first sediment study which popped up in a search refers to C14 dates of 13,000 years ago — so one would expect to find some upset in these nearby sediment layers from a more recent impact.
http://deepblue.lib.umich.edu/bitstream/handle/2027.42/22932/0000498.pdf;jsessionid=E6FE4A66B8673CD8A0645A4DA42FB944?sequence=1
And a glance at these sediment sampling locations across the suggested crater shows that there is data which you can look at to see if these sediments hint at their being splattered around about recently.
http://mi.water.usgs.gov/pubs/WRIR/WRIR98-4039/images/fig3.jpg
http://mi.water.usgs.gov/pubs/WRIR/WRIR98-4039/WRIR98-4039TOC.php
Actually, if one wants to look for underwater craters, I suggest Lake Agassiz. It was a bigger target at the time, and maybe a crater got buried by its sediments. It’s a bit north of the center of the identified splash area, but there are few sample areas to the north so it’s possible that the impact is on the north side of the splash area.
@phlogiston:
The “1500 year” cycle is more likely a range of times with 1200 years at the lower band and 1800 years at the longer. It is an average duration, not a fixed period. The most likely causal agent is the lunar tidal cycle that runs a similar duration, matches the historical temperature cycles, and has more effect on ocean mixing (cold deep to surface) than does the wind. See:
The core of it is here:
http://www.pnas.org/content/97/8/3814.full
while I look at it a bit here:
http://chiefio.wordpress.com/2013/01/24/why-weather-has-a-60-year-lunar-beat/
http://chiefio.wordpress.com/2012/12/15/d-o-ride-my-see-saw-mr-bond/
http://chiefio.wordpress.com/2013/01/04/lunar-cycles-more-than-one/
Per the topic of the Y.D.:
The history of Encke matters… it arrived sometime around 20 kya? then proceeded to break up and give periodic meteor storms for generations (decreasing over time as the debris gets consumed). Tunguska Event was likely from one SMALL left over fragment. The orbit of the earth moves into / out of the center of that debris field on a very long cycle (we are presently nearer the edge, so lower level of impacts than in the past). It is a large debris field from a major break up, so arguments of the form “It is unlikely for many to arrive at once” are broken on the face of it due to this existence proof.
http://chiefio.wordpress.com/2011/11/03/lunar-resonance-and-taurid-storms/
http://chiefio.wordpress.com/2011/11/14/meteor-showers/
It think it is likely essential to address Comet Encke and the breakup history of it, along with known cyclical patterns from our drift into and out of that debris field along with the development of that debris field over time, to have any hope of explaining the last 20,000 years patterns. It was a major change in our “context”…
The “1500” year pattern persists over much much longer time scales, so is much more likely tied to a fundamental property of the solar system. (Be it solar dynamics or orbital dynamics – it’s something outside our surface dynamics that are less stable…) IMHO the best candidate is an orbital resonance based “coincidence” of planetary positions with lunar / tidal ocean stirring; and with a “maybe” of a modulation of solar state / sunspot levels (as either coincident event with no climate impact; or a small potential of coincident event with climate impact). Orbital resonance keeps all those things happening in the same interlocked cycles, so “causality” can not be attributed based on showing frequency of coincident occurrence.
For example: IFF the lunar ocean “stirring” is the cause of cyclical 1500-1800 year cooling / warming cycles (as it looks to me) and is held in phase with planetary orbital positions (via orbital resonance) and those same planetary positions modulate sun spot levels: All three will have very high correlation. But it would be seriously wrong to say either “The planets cycles cause the cold” or “The solar sunspot cycle causes the cold”. It’s the lunar tidal stirring the oceans; the other two are non-causal, just coordinated via orbital resonance.
BTW, the lunar orbital tidal effects account for the known cold events other than the Younger Dryas… which further argues for the Younger Dryas to be “special” and suggests unusual causality such as an impact event.
I tend to waste time reading wild-eyed semi-science, just because you come across some interesting data spliced into the refutable theories. Besides reading the semi-science of various climate scientists, I’ve read the semi-science involving lots of ideas regarding the demise of Mammoths. One work was by a guy who I think was named Graham Kendall, but all my links to his paper have failed.
One thing he stated I always wanted to run by a more qualified geologist, (if only to see eyes roll.)
It was the idea that it had to get cold very fast, for the mammoth flesh to not rot in the middle, where food would ordinarily be decomposing and bloating in a dead beast’s guts, (especially a mammoth’s, because they were so large.) He had interesting ideas about a flash-freezing calamity in the north which we can’t imagine, because we have never seen the likes of it.
He also stated the mud beneath the permafrost is not strata in layers, but rather a sort of churned up muck, holding frozen leaves and twigs that are well preserved, and that oil workers run into such well-preserved evidence of a milder, lusher arctic while drilling. Any oil workers care to comment?
I really enjoyed the fellow’s ideas, even if they were science fiction. One thing he stated was that all the frozen mammoths were found clustered in higher places, as if they had struggled up hill through a calamity.
Anyone know what happened to Graham Kendall’s paper?
Two things. 1 – The KT boundary extinction may have something to do with extraterrestrial impact(s) but, by no means, is it the only driver. Megafaunal decline (dino’s) had been ongoing for several million years prior to the impact(s), as were marine vertebrates and invertebrates. Ocean chemistry at the times indicate significant word-wide changes in overall chemistry that started long before the impacts(s). Large volcanic eruptions (Daccan Traps for one) in addition to elevated rates of seafloor spreading (mid-oceanic ridge eruptions) had a role and, with the exception of the impact(s), were long term environmental changes well under way prior to the boundary extinction. Contrary to popular opinion, the K/T extinction event did not happen by one event (impact) no matter how “romantic” the idea.
2 – There has never been any evidence uncovered that Lake Michigan is underlined by an impact crater although the idea that many of the large structural basins (such as the Michigan Basin) in the North American craton may have had a large impact genesis has been a topic of geological discussion. These “genesis” type impacts would be extremely old (Precambrian > 500 MYBP) and not as recent as the late Pleistocene . That would be an “exceptional claim” type of issue. Pleistocene glaciation created and significantly modified many extremely large land forms,the Michigan Basin is one.
The clues are there. It is a matter of correctly interpreting them. Several decades ago I used to fly over Mellville Island, located in the Canadian Arctic. What appeared to me to be an impact crater on the Sabine peninsula of Mellville Island turns out to be a rather large collapsed salt dome.
You can see the crater using Google Earth at these coordinates: 76.628378N 109.044778W. On radar it appears to have a central rebound rise in the middle of the crater.
Caleb,
There was a very interesting article on mammoths, which I keep losing for some reason. It seems the Wayback Machine changes over time [?!]. I had a much more detailed article bookmarked, but now it is gone.
Here is an abbreviated version of that much longer article, which asks some interesting questions.
One question: what is “muck”? It appears to be some sort of mud, thousands of feet deep in places. At the bottom of the muck is evidence of mammoths, and grasslands, and many other Ice Age mammals. It appears that the mammoths, which numbered in the tens of millions, all disappeared at the same time. When mammoths roamed, the climate in Alaska was much warmer than now.
What caused that mass extinction [which also affected other mammals at the same time]? Some of the mammoths had fresh vegetation in their teeth when they were flash frozen, and their stomach contents were fresh. How did that happen, without putrefication? Many of the mammoths showed signs of being smashed from above, with their legs splayed and broken. Where did the muck suddenly come from? It appears at the same geological time [just prior to the Holocene] over large geographical areas, from Alaska to Siberia and parts of China. A large blob of “muck”, at extremely low temperatures, seems to have descended across vast areas at the same time. How else to explain numerous instantly frozen mammoth carcasses?
The source of the article seems a little wacky, but the questions raised have not been satisfactorily answered, IMHO.
@dbstealey:
One proposal is that the same impact into the ice sheet that caused the Y.D. also kicked up a load of frozen “ejecta” and sent a tidal wave of frozen mixed with mud / slush over the pole to land on top of the Siberian Mammoths. It explains all those odd things in the muck, the ‘flash freeze’, and more. (The only part that bothers me about it still is the question of how to get that much stuff moved in a tidal wave of muck – clay mud and ice – and not heat it enough to melt fully…)
If the strike hit ice, then where would the ejecta originate?
eco-geek says: “…I think there are more important things to worry about than what caused the Younger Dryas….”
Yes. It’s the sun, sagacious.
@Jean Parisot:
As I understand it (which is ‘not well’ – since it’s not my theory and I’m only ‘channeling’ someone else on it š the impact causes a significant vaporization / jet of hot crap downward. This large gas pocket (think minor nuclear explosive force) puts lots of pressure / force on the surrounding ice sheet as the shock wave fractures it. Then the whole mass gets moving from that impact overpressure event. “Steam explosion under ice” writ large… very large…
In reply to:
leftturnandre says:
May 24, 2013 at 3:19 am
@William Howard Astley
William, The Gothenburg geomagnetic flip was an artifac and has never been reproduced. You wonāt find any contemporary publication referring to it. There has never been retractions or refutals, but Itās not there, anywhere.
William:
See the contemporary reference below to the Gothenburg geomagnetic anomaly.
There is evidence of a very large increase in C14 that correlates with the Younger Dryas cooling event. There are papers that assert a reduction in ocean circulation cannot result in an increase in C14 of the magnitude observed.
I believe is other evidence to support the existence of the Gothenburg geomagnetic excursion.
The discovery of cyclic and rapid changes to the geomagnetic field is recent. What is missing is a mechanism that explains what causes the geomagnetic excursions. One hypothesis proposed is that growth or change of the ice sheets causes results in a change to the earthās rotational speed which in turn causes the geomagnetic excursion.
There is a question in terms of ice sheet growth what is the dog and what is the tail. If there is an external forcing function that can cause an abrupt change in the geomagnetic field then the geomagnetic excursion causes the cooling and the ice sheet growth. In the last 10 years there has been the discovery of archeomagentic jerks (spacing roughly 400 years) at which time the geomagnetic field orientation changes abruptly by 10 to 15 degrees. Planetary temperature changes correlate with these changes. The acheomagnetic jerks are captured in fired pottery. The French have thousands upon thousands of pieces of pottery that they have examined.
A geomagnetic excursion is capable (assuming Svensmarkās mechanism is real) of cooling the planet for 1300 years. As noted above a meteoroid or comet impact is not. There still needs to a physical explanation for the 18, plus 2200C burn marks.
http://link.springer.com/article/10.1134%2FS0001433812080063#page-1
The Gothenburg geomagnetic excursion as a chronological marker for the AllerĆød interstadial in the Central Russian Upland
http://cio.eldoc.ub.rug.nl/FILES/root/2000/QuatIntRenssen/2000QuatIntRenssen.pdf
Estimates for the increase in Delta 14C at the start of the YD all demonstrate a strong and rapid rise: 40-70%/% within 300 years (Goslar et al., 1995), 30-60% in 70 years (BjoK rck et al., 1996), 50} 80&in 200 years (Hughen et al., 1998) and 70& in 200 years (Hajdas et al., 1998). This change is apparently the largest increase of atmospheric 14C known from late glacial and Holocene records (Goslar et al., 1995). Hajdas et al. (1998) used this sharp increase of atmospheric 14C at the onset of the YD as a tool for time correlation between sites.
http://www.sciencedaily.com/releases/2012/10/121016084936.htm
http://www.mendeley.com/research/paleoclimatic-context-geomagnetic-dipole-lows-excursions-brunhes-clue-orbital-influence-geodynamo/
@Jean Parisot:
It just occurred to me that we may be using ‘ejecta’ in two different ways. I’m using it to mean “anything ejected – mud, ice, whatever” where I think you might be meaning “solid non-ice matter like clay, rock, dirt”.
Picture a 1 mile wide space rock hitting a 1 mile thick ice sheet. It is coming in at 24,000 mph. That means that the front edge goes from top of ice sheet to touching bedrock in 1/24,000 of an hour. 1/400 th of a minute. 1/6 of a second. It creates a massive explosion as all that energy is liberated in factional second time scale in a ‘solid on solid’ impact. That vaporizes everything (including the rock of the space rock) and makes a giant steam pocket (of intense pressure as everything is still in the same space as the original solids, just very very hot now…)
That is when things can physically start to move as ‘ejecta’. From that 1 mile “spot” of nuclear bomb type pressures and temperatures. Any actual solids will be from significantly outside that “spot”, as that spot is more like plasma / explosive-mid-detonation than solid…
The “thesis” (as I understand it) is that such an impact happened, and the “scouring” marks on the rock level is seen in some areas; but the base rock layers don’t have a ‘crater’ as that 1 mile ‘crater’ event was in the ice (which then made the superheated steam / gasses that scoured the flat rock layer and picked up and tossed more of the surviving soil / ice layers around it)
This would be a lot better as an animation…
@William Howard Astley
Thanks for the Gotheburg flip reference I’ll send that to Prof Langereis, ..
http://www.geo.uu.nl/~forth/people/Corl/corl.htm
…who told me about the failed duplication hunt for the Gothenborg flip. Strange that the thousands of papers about the late glacial oscilllations don’t mention it, whilst routinely researching the magnetic susceptability.
The 14C spike at the beginning of the YD is another artifact caused by a counting error in the grey scale record in the Cariaco basin, which is evident in the INTCAL04 calibration table. However, due to multiple problems in chronology, that record was removed in INTCAL09 with as consequence that this spike also disappeared:
Just plot the delta14C values for INTCAL04 and INTCAL09
http://www.radiocarbon.org/IntCal04.htm
http://www.radiocarbon.org/IntCal09.htm
But of course it will linger on for decades in the Younger Dryas studies.
RE: dbstealey says:
May 24, 2013 at 9:24 am
That’s it!!! Thanks a million!
I had forgotten what good reading it makes. Even if it is balderdash, it is good balderdash, with much more interesting stuff than one lone Yamal larch tree, used to create a world-wide hockey stick.
Now what I have to do is find a chat-room where geologists hang out, and ask a lot of questions about arctic muck, and where it came from.
Either that, or I’ll write an article and submit it here. (I’ve always wanted to be a muckraker.) I’d soon hear from WUWT readers, and learn where I was in error.
From the mammoths to the Vikings, the arctic holds all sorts of mysteries. I wish the politicians would just buzz off, and leave scientists alone to uncover the wonders all around us.
Clearly the only possibility is a non condensing greenhouse gas sucking meteorite because the models can only reproduce such rapid cooling by removing these gasses from the atmosphere.
Caleb,
I would be interested in reading more about “muck”, if you’re thinking about writing an article. It is a mystery. What is it? Where did it come from? Outer space? Did it rain down at ā3ĀŗK, and freeze everything it covered?
Muck is apparently very widespread on the planet, and forms a deep layer. The Russians drilled through thousands of feet of featureless muck, until they found evidence of prairie-like grasslands underneath.
This event occurred not all that long ago [during the Pliocene, IIRC]. Tens of millions of mammoths, maybe many more, became extinct overnight. What happened?
The climate apparently changed drastically; hippos and rhinos had roamed Alaska and Siberia, in what was a very temperate climate. Now they’re gone, all of them. It’s a mystery, and very interesting.
There are a number of “prairie pothole” lakes that are quite round and have central islands. There can be other explanations, but if on Mars, the first assumption would be craters. There is a large circular feature on the Minnesota/Wisconsin border roughly between Eau Clare and La Crossethat is reminiscent of a buried and excavated crater, which doesn’t mean that it -is- and certainly would be much older than the Younger Dryas. Just like the arc on Hudson’s Bay and another in the Maritimes, it is interesting.
EM Smith, I am considering the ejecta, especially the plant matter and silica, that was formed under pressure into the unique micro-spheres that are a signature of a cosmic event. Does that process happen in a secondary steam blast? A that be duplicated in the lab?
And can that … (Typing on a tablet is trying)
Any cosmic impact of such consequence as to alter global climate drastically will leave an unmistakable crater, no guessing games needed. Micro-sperules rain constantly on the planet. This subject is a corner of geology known as “impact studies” and the would-be climatologists should leave such questions to those who know the subject of cosmic impacts.
dbstealey says:May 24, 2013 at 9:24 am
I remember a ‘Frozen Mammoth’ article in Nat’l Geographic. Could have been in the 50s or early 60s issues. The meat was allegedly flash frozen, and still ‘fresh’, as eaten by a stranded expedition.
@ Matt says:
May 24, 2013 at 2:03 am
āI must say that āāExtraordinary claims require extraordinary evidenceā is drivel. What extraordinary evidence did Einsteinās claims need for support? One astronomical observation that may anyway not have been precise enough to do the job. ā
This is utter nonsense.
***Sagan’s requirement thus stated is obviously a highly subject demand. What is “extraordinary?” It is better to formulate it: “More fundamental conjectures require more fundamental proofs.”
I have a corroborating bit of evidence supporting a southern Lake Michigan proposed impact site. There are some associated ejecta or fragment impact features with this proposed primary impact location that have no other generally accepted explanation at this time: Carolina Bays — See generally: http://en.wikipedia.org/wiki/Carolina_Bay
Carolina Bays are elliptical depressions that appear anomalously across the Southeastern inland sedimentary landscapes from Alabama to Virginia and predominating in — you guessed it , the Carolinas and the long axes of these features show consistent trends and converge — on southern Lake Michigan.
See here: http://abob.libs.uga.edu/bobk/cbfig5.gif (you can overlay the image on Google Earth to see the extended long axis trend lines at the proposed site in southern Lake Michigan).
Some of the “prairie potholes” in the Midwest have similar features to the Carolina bays. A substantial body of these also have a long axis convergence trend on southern Lake Michigan.
http://cosmictusk.com/wp-content/uploads/Midwest-bays-long-axis-1024×690.jpg
http://cosmictusk.com/perigee-zero-carolina-bays-in-the-midwest/
The nature of these Carolina Bay sites could not have been from solid meteorite impacts as the typical impact characteristcs of those objects at such as site are entirely absent in Carolina Bays. They have fit however some ideas about possibly low velocity prograde orbit cometary fragment impacts. See here: http://abob.libs.uga.edu/bobk/cbayint.html
But if they fit data and concepts about low velocity cometary ice impacts — then they could ALSO very easily fit a theory of secondary ice eject impacts caused by surviving ice thrown clear from a primary impact site on a massive ice sheet.
Food for thought.
G.R. Mead
@Steve Keohane
Flash frozen mammoths is just a rural legend. In the last decades, several mammoth mummies have been found after the legend was created, ie the Jarkov Mammoth, the Fishhook mammoth, the Yukagir mammoth, Luba the baby mammoth. All highly googleable. The common factor with all of them is water, marshes, swamps, bogs, they probably drowned and became naturally mummified due to peat acids.
Dude, don’t quit your day job.
Proelior you left out the following (forgive me for using Wikipedia as a “cringe” scientific source)
Theories of origin Carolina Bays
More than a dozen bays are shown in this photo in southeastern North Carolina. Several are cleared and drained for farming.Theories of the origin of the Carolina bays fall into two major categories: that these features were created by forces within the Earth, or that they were gouged by an astronomical event or set of events.
Geomorphology
Various geomorphological theories have been proposed to account for the bays, including action of sea currents when the area was under the ocean or the upwelling of ground water at a later time. One major theory within the earth sciences academic community is that a combination of processes created the shapes and orientations of these ancient landforms, including climate change, the formation of siliciclastic karst by solution of subsurface material during glacial sealevel lowstands and later modification of these depressions by periodic eolian and lacustrine processes.
Various proposals that they were either directly or indirectly created by a meteorite shower or exploding comet are disputed by many scientists for an apparent lack of extraterrestrial material, absence of shocked quartz and “bedrock” deformation associated with larger bays, and extremely low ratio of depth to diameter of the larger bays. More information on these theories can be found at: Carolina Bays.
Quaternary geologists and geomorphologists argue that the peculiar features of Carolina bays can be readily explained by known terrestrial processes and repeated modification by eolian and lacustrine processes of them over the past 70,000 to 100,000 years. [2]. Also, quaternary geologists and geomorphologists believe to have found a correspondence in time between when the active modification of the rims of Carolina bays most commonly occurred and when adjacent sand dunes were active during the Wisconsin glaciation between 15,000 and 40,000 years and 70,000 to 80,000 years BP [3]. In addition, quaternary geologists and geomorphologists have repeatedly found that the orientations of the Carolina bays are consistent with the wind patterns which existed during the Wisconsin glaciation as reconstructed from Pleistocene parabolic dunes, a time when the shape of the Carolina bays was being modified [4].
Impact event
The cometary impact theory of the origin of the bays was popular among earth scientists of the 1930s and 40s. It said that they were the result of a low density comet exploding above or impacting with the Laurentide ice sheet about 12,900 years ago.[1]
New hypotheses arose again in the 1980s and 1990s, spurred on by various attention to impacts such as the Tunguska event, CretaceousāPaleogene extinction event and a theorized link to the unsolved scientific mystery of the Younger Dryas event. Impact geologists determined the depressions are too shallow to be impact features. Reports of magnetic anomalies turned out not to show consistency across the sites. There were no meteorite fragments or impact crater geologic structures. None of the necessary evidence for an impact was found. The conclusion was to reject the impact theory at the Carolina bays.[2
http://en.wikipedia.org/wiki/Carolina_Bay
phlogiston says:
May 24, 2013 at 5:35 am
Note the author is not questioning the existence of the D-O events but calls them instead quasi-periodic, and suggests that the very regular 1500 year signal might be an aliasing artefact, not the real D-O events. The many posters here who regularly refer to the 1500 year periodic events needs to address this possibility.
Yes, there is no 1500-yr cycle. That value is likely to be an artifact of averaging: http://www.leif.org/EOS/Obrochta2012.pdf “Our new results suggest that the ā1500-year cycleā may be a transient phenomenon whose origin could be due, for example, to ice sheet boundary conditions for the interval in which it is observed. We therefore question whether it is necessary to invoke such exotic explanations as heterodyne frequencies or combination tones to explain a phenomenon of such ļ¬eeting occurrence that is potentially an artifact of arithmetic averaging.”
Thank you, I have found the extinction of the North American mammals very interesting. I was taught that they were hunted into extinction. I found this strange since there are still elephants in Africa. There must have been much easier prey than a Mammoth or Sabre Tooth. Really.
My theory for the hole in Lake Michigan, the rise to the north served as a small glacier dam or fall. The depression is the same as you would find in a stream or river that flows over a similar embankment. There is always a deep spot. The geology of the area is a major factor of which I know nothing.
My theory on the extinction; large herbivorous mammals were hit by repeated catastrophic flooding on new grasslands (on floodplains) as the glaciers retreated. One of many possible factors. It’s a 12,000 year old mystery. I found the comments very informative.
Love this topic, Thanks
The Carolina bays are now thought to be caused by peat fires. Not to be associated with the Younger Dryas.
http://www.sciencedirect.com/science/article/pii/S0033589411001438
“As a footnote, an impact with the ice sheet and its catastrophic effects could explain the other primary explanation of the source for the Younger Dryas. An asteroid strike leaving one or more craters in the Great Lakes area could have resulted in a rush of fresh water flowing either north into the Arctic or out the St Lawrence Seaway and shutting down the North Atlantic conveyor transporting heat from the equator. Thus, the two theories would merge into a progressive explanation of the sudden cooling, its long duration and the deaths of the megafauna.”
While this can only be the very remote possibility of this scenario supporting the observed ocean circulation change in the North Atlantic. A major problem lies here where an impact big enough to bring down a massive ice sheet would not just melt it and flow down near it’s impact. There would be massive evaporation of the ice sheets which would be thrown miles into the atmosphere all around.Hence, the moisture from the ice would not just flow down into the North Atlantic ocean, but dispersed all over the northern hemisphere.
This wouldn’t cause enough ice melt to be concentrated in just one area of the the North Atlantic for disrupting the conveyor. A rapid natural warm up and melting without an impact would be a much better alternative for this trigger. The flow of melting ice would have flowed in rivers converging into bottlenecks flowing towards the North Atlantic Ocean. A small asteroid strike would keep most of the water from the melt in similar place, but wouldn’t have enough energy to melt most of the ice to have such an ocean conveyor effect..
E.M.Smith says:
May 24, 2013 at 9:02 am
Thanks for the Charles Keeling paper – a less known but much more significant contribution to climate knowledge than his famous CO2 volcano measurements. Yes lunar tidal stirring sounds very plausible as a climate forcing mechanism, I have argued many times that vertical ocean mixing alone is a sufficient and strong cause of climate cooling – due to the obvious fact of sharp thermal stratification. However for this forcing to be strong, and the cooling episodes to follow the 1500-1800 cycle directly, is only one possibility; the other is weak nonlinear forcing, which would cause a much more complex, less predictable temporal pattern. The oceans have their own internal dynamics. Periodic nonlinear forcings can be weak as well as strong.
I was unaware of the comet Encke debris field. There is some scary stuff out there. I dont exclude an impact at the YD, but I feel the ocean is a more plausible factor for millenial scale climate shifts. Do you have any thoughts about the inter-hemispheric bipolar seesaw? Its also a real climate factor, one of many that AGW scientists have sought to misinterpret as CO2 forcing. It is one of a crowded room of proposed YD causative factors, but its the one my money would be on.
Judging from the locations found of the evidence, there is little likelihood of the impact being in the Great Lakes unless prevailing winds during that period were the reverse of what they are today. Most of the debris would form a pattern much like the pattern of tuff left from a volcanic eruption.
One must also explore the possibility that over thousands of years, air bursts built up a lot of this material in glacial ice. When the glaciers melted, a lot of this was left with the other loess from the glaciers and was blown around with the wind. We could well have a layer of these spherules that were simply accumulated over time in the ice, deposited when the ice melted, and blown with the wind.
Also, think for a moment how much of these would have accumulated in Lake Bonneville and Lake Lahontan sediments over time and then blown around with the wind once those lakes dried up. Also, I would be willing to bet there were some serious fires in the Great Basin once those lakes dried up and the trees/grasses supported by all that water died. In fact, not having that great source of evaporation in the Great Basin likely created a massive change in climate. Most of Northern Nevada was a huge lake. Most of the peaks would have been covered with ice. These lakes and the ice would have accumulated debris from air bursts over time.
Do we know that the age of all of this debris is the same? We know it was DEPOSITED at about the same time, but we don’t know that it was CREATED at the same time.
I think a good test would be something like this:
Check the for the population of spherules going back to the glaciation before the Eemian Interglacial. Now check the populations of them over time. Do we see reduced populations of shperules during a glacial period, a layer of high density of these, and then a generally higher population of them during the interglacial than during glacial periods? I would expect to find that during glacial periods, spherules formed from air bursts would get accumulated in ice. As the ice melts, we have a large population of them that gets spread around and deposited from wind blown glacial loess and then we see the usual deposition rate. Then as we go into a glacial period, the deposition rate would reduce as more of them are trapped in ice again.
100.000 years of ice would get pretty dusty/dirty. A lot of those spherules would make it to the bottom of the glacier but would still be covered with ice until the glaciers melt. As they melt, there are no plants to keep the loess in place so it blows around as it dries out.
http://www.climatestudies.unibe.ch/students/theses/msc/45.pdf
So maybe “Younger Dryas” events are normal coming out of ice ages but I am guessing they can vary wildly. If a glacial lake dam bursts very suddenly, it can certainly have a different impact than if it bursts gradually. By that I mean, where a breakout occurs and the nature of the location probably has a lot to do with how quickly a lake empties. If water overtops an area of rock and gradually cuts down into it, that is probably different from a huge wall of ice suddenly giving way at once. The conditions of each interglacial is somewhat random.
The pre-Younger Dryas development of Lake Michigan, and in particular the “South Chippewa Basin” feature in the south end of it, is reasonably well-known.
This basin, put forward here as a possible crater, tied to the onset of the YD, was one of the early features of the proto-Great Lakes to emerge, as the south edge of the continental icesheet began to recede at the end of the last Ice Age.
This depression, now forming the south end of Lake Michigan, is clearly shown by standard geology to have existed for more than 1,000 years before the Younger Dryas.
See Lake Chicago, and in particular the Stages of development of the Great Lakes graphic.
The hole was already there.
@ Matt:
“This is utter nonsense. Itās not like Einstein came up with an outlandish idea, and as soon as the first confirmation came in, everybody took his good word for it ever since.”
Nor did I claim that that’s what happened. Einstein did what Newton did – provided a new way of looking at heaps of old – and therefore not extraordinary – data. Lots of people were converted to his view pretty quickly, and celebrated their relief that Eddington’s data showed no flaw in Einstein’s picture. I’m right and you are wrong: there was no extraordinary data necessary for Einstein’s new ideas to triumph. Nor for Clerk Maxwell’s nor Planck’s nor Newton’s.
Naturally because these have all been routine parts of Physics pretty much since their discoveries, you can argue if you wish that now they are tested each time any experiment is done, but so what? All the canon of theory is tested the whole time. You are so wrong that I suspect you have a reading comprehension deficit.
crosspatch says:
May 25, 2013 at 3:40 pm
…
So maybe āYounger Dryasā events are normal coming out of ice ages but I am guessing they can vary wildly…
If bipolar seesawing characterised the run-up to the latest transition to (the Holocene) interglacial then its not too far-fetched to imagine that it might also characterise the prelude to other interglacials. Maybe its an unstable excursion that pushes the system into a different attractor across a phase-space saddle.
I apologize for the intrusion in the conversion but would like any thoughts on underwater explosions as opposed to air burst events and impacts. Would there be any remaining chemical or geologic signature if a large underwater methyl hydrate explosion occurred 13,000 years ago in the Gulf of Mexico or in Lake Michigan?
HI JudyW,
There are features on the ocean floor that clearly represent events that may then have various causes. Some resemble subsidence, and the suggestion/interpretation has been, that these could be due to hydrate outgassing/destabilization.
Release of gasses from hydrate-formations (and collateral/attendant melting of ice) may not be “explosive” in nature, but such events could cause slides, and otherwise generate tsunamis. They might affect the atmosphere, at least briefly. They do/can leave marks on the ocean floor. Dating these features, and tying them to other events in the geologic past, is of course a separate large challenge.
Ocean bathymetry can be obtained. Articles in this general topical area do exist. A Naval Academy instructor is the author of a “MicroDEM” GIS software, with a heavy emphasis on maritime GIS applications, and bathymetry. Other applications, and data are available (NOAA, NASA).
The general idea is not bad. As usual, the devil is in the details. There is some scientific & public policy “concern” with (roughtly) the possibility you allude to, though mainly in terms of contemporary hazards. The general area you are looking at is a bit dominated/skewed by those hoping to use it in pursuit of Climate Change goals, which can muddiy the waters at bit, for straight science-questions.
Ted
As posted recently in WUWT, Santa Barbara’s Emeritus Professor J.P. Kennett’s report of his YDB (“Younger Dryas Boundary”) Research Group seems definitive: Since globally dispersed micro-spherules only form at temperatures exceeding 2,200 degrees Celsius, while nucleo-chemical analysis precludes any lightning-strike, super-volcano, or other terrestrial processes, trans-continental “strewn-fields” of impact-fused/striated nodules can only have resulted from a major series of air-bursts or relatively small-scale chains of cometary/meteorite impacts.
As the contemporaneous “black mat” above Clovis Culture and extinct large-mammal species’ fossil-beds attests, this rain of exo-solar debris –likely originating in disruption of the solar system’s far-distant, spherical Oort Cloud– likely caused continent-wide wildfires whose atmospheric dust and smoke radically reduced plant cover and subsequent re-growth, starving large Mesolithic herbivores and predators alike.
Despite the well-defined Cretaceous/Tertiary (K/T) Boundary, wholesale destruction of late saurian species remained problematic pending Luis and Walter Alvarez’s discovery of Chicxulub’s submerged crater in the Yucatan. Even so, given events such as the Tunguska air-burst of 1908, a Younger Dryas crater in Lake Michigan or elsewhere would only confirm the obvious: That an anomalous 1,500-year “cold shock” radically cooled Earth’s atmosphere in months, coincident with catastrophic global extinctions affecting human socio-cultural milieus.
Certain chronologies indicate that, for whatever reason, Planet Earth risks major geophysical trauma approximately every 3,600 years. Setting exo-planetary Younger Dryas impacts at BC 12,400 – 12,800 readily conforms to this conjecture.
The impact hypothesis leaves unexplained the Oldest Dryas (18-15 Ka) & Older Dryas (~14,050-13,900 BP, but not well constrained) cold snaps. Same goes for stadials in previous deglaciations.
Good information Ted. Thanks for the response and references to pursue.
Judy, there is evidence for methane hydrate destabilization at the Amazon river fan in the period preceeding the Younger Dryas.
http://www.geog.ucl.ac.uk/about-the-department/people/academics/mark-maslin/Maslin%202009%20Amazon.pdf
See table 1 page 136, the mass transport deposit event in the eastern fan at 13,500 or 14,500 years ago, but obviously very tentative.
What an excellent paper and study leftturnandre! It does appear in the Amazon fan study that the outgassing associated with landslides and avulsion events happened when sea levels were falling. Most were prior to the onset of the Younger Dryas. These releases potentially could contribute to restarting the current interglacial period but I will rule out my explosion hypothesis . Thanks for the enlightenment.
I wonder what sort of extinction event would be required to remove the dinosaurs of Climate Change from the historical record?
A new ice age with all the windymills frozen solid?
@leftturnandre May 25, 2013 at 12:31 am:
“The Carolina bays are now thought to be caused by peat fires. Not to be associated with the Younger Dryas.”
andre – There is NO consensus whatsoever on the cause of the CBs. NO single explanation has been able to explain them. ALL explantions are inadequate, even though the aeolian people CLAIM they have the answer. However that explanation has been ruled out several times over the last 60+ years. With no single explanation being adequate, several attempts have been made using sequential causes. None of those is adequate, either, not yet.
Saying that peat bogs “are now thought to” be the cause is useless. ALL the explanations are “thought to” explain the CBs. The problem is that none of the purported “thought to”s survive a reality check.
As to the dating, you are correct that the OSL and C14 dating have put the CBs at an earlier time than the YDB. At this time I am TRYING (amd not getting very far) to assess where the samples came from in the CB sites. The choice of sample points is important, because the quartz sand overlaying the bays is laid in one layer (without strata), a layer sometimes 10 meters thick. And samples from inside the bays give different readings from outside and from the rims. The very little info I’ve gleane from papers says that Clovis artifacts were found in the “subsoil” under the sand, some of them on the rims and some not. Clovis dates from 13.5-12.8 kya. This conflicts with the OSL dating on the sand of ~45 kya and others at ~130 kya: A 13kya relic should not be under 130 kya sand. I suspect that I am misreading the papers and their meanings somehow, but my search for further information is being hampered by firewalls and my limited retiree budget.
Steve Garcia
@Phlogiston:
If you look at this graph:
http://theinconvenientskeptic.com/wp-content/uploads/2010/11/LI-Holocene.png
that I reference here:
http://chiefio.wordpress.com/2012/12/29/annoying-lead-time-graph/
You will notice that the Antarctic doesn’t have a big “dip” like Greenland during the Dryas events. It has a ‘go flat’ at most (and that only in the most recent, the early one just keeps climbing…)
So first “take away” is just that the Dryas events are much more hemispheric (at most) than global. (And likely even limited to the end of the Gulf Stream heat delivery…)
The second “take away” is that it was during a time of strongly increasing insolation, but prior to full stability levels.
Third “take away” is that we’ve been in a 9000 year very slow cooling and with rapidly dropping insolation. We’re now in a place where when an ice / snow field starts to form, it will be a very positive feedback into a frozen Popsicle land and there just isn’t enough sunshine to stop / reverse it. Last time we were at these insolation levels we were in a glacial period prior to the Elder Dryas. And nothing prevents us from once again achieving stability in such a glacial state…
One “good thing” is that our present seasonal cycle has us warming in the northern hemisphere while the southern cools:
http://chiefio.wordpress.com/2013/02/11/interesting-change-of-season-length/
So look at this graph referenced in that article:
http://individual.utoronto.ca/kalendis/solar/Season_Lengths_30K.png
and you can see that there’s excellent reasons for shifts of Arctic vs Antarctic ice levels as the season lengths move in opposition with orbital changes. There is a fundamental “polar season seasaw”. (There are also more weather shift related oscillations between the two poles).
So, IMHO, there’s nothing at all unexpected about having shifts of more or less ice at one pole, with the opposite happening at the other pole. It is absolutely to be expected and normal.
Now look back at about the 10ky BP to 12 ky BP cycle point. That’s when N.H. summers were more strongly cyclical and nearing a very much shorter end of the range. About 5 days shorter than now. That can explain being cold, but not a “sudden” return to cold (as it takes about 10,000 years to go from one extreme to the other).
Is there some other cyclicality that could act faster, on the order of 1,000 years seen in the Y.D. duration? Only the lunar cycles, near as I can see. Yet they don’t line up with the Y.D. event (the only cold excursion where they do not…) and that, then, argues for some extraordinary out of cycle event; like a big rock fall into ice disrupting the ocean flow / cycles.
It looks like there is a tendency for the times when the thermohaline circulation slows for heat to ‘stack up’ in the southern ocean / tropics. That gives a very cold Arctic / EU and a very nice Australia / Middle Americas. So what causes the quasi periodic circulation slowing? Nobody knows… but it looks like part of the answer is lunar / tidal cycles, part might be a solar / UV component (or it might be a confounder simply in sync due to orbital resonance but with no causitive power), and part might be a natural oscillation time period of oceans. But when it happens, the Arctic gets damn cold, and the Antarctic warms a bit. (Whereas right now we are getting the opposite. Arctic is low on ice and Antarctic is growing well. Then again, N.H. summers and insolation have been getting longer for a few hundred years… due to those orbital changes).
Hope all that helps…
@Jean Parisot:
It’s not “just steam”. It’s a nuke like event moderated by a mile thick layer of ice that turns to steam… but with a large meteor core that still can make lots of interesting micro-spheres… and some amount of “crap” in and under the ice that also can make interesting bits.
What the ice does mostly is not prevent all aspects of a “crater in the dirt”, but just most of it and turn a lot of the rest into more “scour and eject” rather than “crater and eject”. You still get a large layer of a lot of stuff picked up and ejected with great violence and energy.
Somebody must have a simulation of this online somewhere…
@crosspatch:
We have two stable modes and a metastable transition mode. The two stable modes are “Glacial frozen” and “interglacial”. During a glacial frozen we get periodic (about 1500 to 1800 year) attempts to warm that show up as “spikes” of warmth, but rapidly fail back to frozen cold. During interglacials we get sporadic (about 1500 year) attempts at cold excursions, but they can’t “latch up” into cold frozen. Only during the transition is it unstable enough to ‘latch up’ either way. So we can, during those times, get Y.D. type events.
http://chiefio.wordpress.com/2012/12/15/d-o-ride-my-see-saw-mr-bond/
references:
http://www.pik-potsdam.de/~stefan/Publications/Nature/rapid.pdf
and further down:
IMHO, they pretty much nailed it. The 1500 ish year cycle is always there, but the ocean system is only sensitive to it in some modes (especially when glacials are happening).
At the transition point out of glacials, we are still relatively unstable and modest push in either direction can result in large responses ( I.e. “Dryas” like events ought to be common both at exit and entry to glacial conditions… so as we exit the high insolation at 65 N of the interglacial regime happening now we ought to be ever more unstable to excursions…)
@E.M.Smith
You contend that the Younger Dryas was restricted to the northern hemisphere and likely only to the “the end of the Gulf Stream heat delivery”
I agree with the formr but not with the latter. Evidence for the Younger Dryas has been found in the Cariaco basin, Venezuela, Santa Barbara basin California (ODP site 893) and several speleothems like the Hulu cave China, Klamath mountains Oregon (see: http://www.geo.oregonstate.edu/files/geo/Vaccoetal_-2005-QR.pdf)
However indeed several palynologic and other paleo biologic records do not show signs of cooling and that is simply because the Younger Dryas was not a cold event but a dry event.
That’s explained here in this work in progress paper (I linked to that before)
https://dl.dropboxusercontent.com/u/22026080/YD%20working%20paper.pdf
Andre
In reply to:
lsvalgaard says:
May 24, 2013 at 3:02 pm
phlogiston says:
May 24, 2013 at 5:35 am
Note the author is not questioning the existence of the D-O events but calls them instead quasi-periodic, and suggests that the very regular 1500 year signal might be an aliasing artefact, not the real D-O events. The many posters here who regularly refer to the 1500 year periodic events needs to address this possibility.
lsvalgaard says:
Yes, there is no 1500-yr cycle. That value is likely to be an artifact of averaging: http://www.leif.org/EOS/Obrochta2012.pdf āOur new results suggest that the ā1500-year cycleā may be a transient phenomenon whose origin could be due, for example, to ice sheet boundary conditions for the interval in which it is observed.
Your comment is in correct. The paper you quote is garbage as ignores observations that unequivocally proves that the D-O cycles are caused by solar magnetic cycle changes. (The key point is explaining the polar see-saw. The authors of the garbage paper ignore the polar see-saw. The polar see-saw is an observational fact and must be explained. Svensmarkās mechanism explains both the D-O cycle and the polar see-saw. There is no alternative mechanism provided.)
First point, an observation not a theory.
The Dansgaard-Oeschger warming and cooling ācycleā occurs with an interval of 950 years, 1350 years, and 2000 years. That is a fact not a theory.
Greenland ice temperature, last 11,000 years determined from ice core analysis, Richard Alleyās paper.
http://www.climate4you.com/images/GISP2%20TemperatureSince10700%20BP%20with%20CO2%20from%20EPICA%20DomeC.gif
The authors provide no mechanism of āice sheet boundary conditionsā that could cause what is observed. The warming and cooling could also be due to a fairy with a magic wand. The point is the authors must provide some high level mechanism by which āice sheet boundary conditionsā can cause the cyclic warming and cooling in both hemispheres on two different ice sheets and what would cyclic change āice sheet boundary conditionsā. They do not explain the mechanism as there is no mechanism by which āice boundary conditionsā can change cyclically for some unexplained reason and even if āice boundary conditionsā did change cyclically there is no explanation as to how the cyclic ice boundary conditions could cause the Greenland Ice sheet and the Antarctic ice sheet to simultaneously change temperatures (Polar see-saw) (William: No explanation of even what ice parameters could possibly change to cause what is observed. The paper does provide a strawman mechanism as how ‘ice boundary conditions’ could cause ‘cyclic’ warming and cooling as there is no possible mechanism.)
The true purpose of the paper you quote is a hand waving attempt to hide the fact that the D-O ācycleā and the Heinrich ācycleā is caused by solar magnetic cycle changes. i.e. The garbage paper is a ‘warmist’ paper that is written for the climate war.
Svensmarkās analysis that shows the polar see saw (Antarctic ice warms when Greenland Ice sheet cools) is simultaneous which proves that solar magnetic cycle changes drive the D-O cycle, as cloud modulation by the sun affects both hemispheres simultaneously.
There is no other mechanism that can affect the Greenland and Antarctic ice sheets simultaneously. Cloud modulation can. That proves that D-O cycle is caused by solar magnetic cycle changes.
The affect is different for Antarctic ice sheet as the albedo of the Antarctic ice sheet is higher than clouds so the net effect of an increase of cloud cover is a slight warming of the Antarctic sheet.
If it is fact that solar magnetic cycle changes are causing what is observed then the question of what is the solar ācycleā.
āHowever, neither the last glacial nor Holocene HSG records exhibit statistically significant 1500-year periodicity. Therefore these records were referred to as either āquasi-periodicā (Bond et al., 1997) or ācyclicā (in a geologic sense, implying repetition, not periodicity) (Bond et al., 2001). The mean pacing of 1470 +/- 523 years was derived by interval counting (the elapsed time between cycle midpoints) and was the combined result of a composite record covering the last glaciation with V23-81 (1536 +/- 563 years) and the Holocene with V29-191 (1374 +/- 502 years) (Bond et al., 1997). Bond et al. (1999) later revised the V23-81 result to 1469 +/- 514 years and presented results for the last glacial interval of DSDP Site 609 (1476 +/- 585 years).
If the Site 609 HSG variability is indeed solar in origin, a more parsimonious explanation is that it is directly related to the observed variability in the inferred forcings, the w1000- and w2000-year periods that are present in both Holocene atmospheric 14C production and ice core 10Be flux (Fig. S4).ā
http://arxiv.org/abs/physics/0612145v1
The Antarctic climate anomaly and galactic cosmic rays
Borehole temperatures in the ice sheets spanning the past 6000 years show Antarctica repeatedly warming when Greenland cooled, and vice versa (Fig. 1) [13, 14]. North-south oscillations of greater amplitude associated with Dansgaard-Oeschger events are evident in oxygenisotope data from the Wurm-Wisconsin glaciation[15]. The phenomenon has been called the polar see-saw[15, 16], but that implies a north-south symmetry that is absent. Greenland is better coupled to global temperatures than Antarctica is, and the fulcrum of the temperature swings is near the Antarctic Circle. A more apt term for the effect is the Antarctic climate anomaly.
Attempts to account for it have included the hypothesis of a south-flowing warm ocean current crossing the Equator[17] with a built-in time lag supposedly intended to match paleoclimatic data. That there is no significant delay in the Antarctic climate anomaly is already apparent at the high-frequency end of Fig. (1). While mechanisms involving ocean currents might help to intensify or reverse the effects of climate changes, they are too slow to explain the almost instantaneous operation of the Antarctic climate anomaly.
Figure (2a) also shows that the polar warming effect of clouds is not symmetrical, being most pronounced beyond 75ā¦S. In the Arctic it does no more than offset the cooling effect, despite the fact that the Arctic is much cloudier than the Antarctic (Fig. (2b)). The main reason for the difference seems to be the exceptionally high albedo of Antarctica in the absence of clouds.
I find it surreal, absurd, and inconceivable that solar cycle 24 is the start of either the cooling phase of a D-O cycle or more likely a Heinrich and there are no discussions of the solar anomalies.
Based on the paleo record, the planet will cool.
William Astley says:
May 27, 2013 at 1:14 am
In reply to:
lsvalgaard says:
May 24, 2013 at 3:02 pm
phlogiston says:
May 24, 2013 at 5:35 am
Attempts to account for it have included the hypothesis of a south-flowing warm ocean current crossing the Equator[17] with a built-in time lag supposedly intended to match paleoclimatic data.
The term for this across-equator heat transport is “heat piracy”. At present this is taking place from the South to the North Atlantic in the form of the Carribean current (“pirates of the Carribean!”). Heat piracy is considered to be an important part of oceanic dynamics of bio-polar seesaw – or the “Antarctic anomaly” as you prefer to call it.
You mention a lot of important facts and observations, such as about the Antarctic anomaly and the anomalous Antarctic albedo. However a general comment I have about many of the posts here is that I feel they are inappropriately atmosphere-centric. This is part of the fallacy of CAGW that the ocean is ignored (except – comically – when atmospheric global warming stops so it has to become deep ocean warming – safely out of reach of any meaningful observational data – but I digress..). In CAGW every 20th century temperature wiggle has a “dark satanic mills” mythical anthropogenic explanation – early century warming was from increasing CO2 input – but then in the 50’s we started emitting soot particles which cooled us down, until in the 70s USA and Europe cleaned up their act, emitting “pure” CO2 again so we started warming, but then along came the Chinese and Indians with soot particles again so the cooling levelled off.
Here at WUWT the CAGW bluff has been called, but all the YD explanations are again atmospheric. I think this is wrong, and believe there is truth in the phrase “weather comes from the atmosphere, climate from the ocean”. There is as I have described a well established science of how oceanic oscillations in deep water transport can account for climate fluctuations on century and millenial scales, as well as the Antarctic anomaly. Take for instance this paper by Seidov and Maslin 2001 which provides a plausible model on how heat piracy and the north Atlantic deep water (NADW) circulation account for the bi-polar seesaw and even the D-O and Heinrich events.
On the scale of events such as the YD, “instantaneous” can mean plus or minus a century or three.
E.M.Smith says:
May 26, 2013 at 11:26 pm
The first graph you show is helpful, it broadly concurs with figure 2 in Blunier et al 1997.Between 17000 and 15000 Ya the Antarctic sharply warms while Greenland cools slightly. Then between about 14500 and 13000 Ya Greenland becomes abruptly warmer, although the warming is all at the start in a sharp increase followed by a cooling trend. During this period – after a delay of about 1000 years, the Antarctic cools slightly. You refer to this as a “levelling off”, although this phase is generally referred to as the “Antarctic cooling reversal”. Then comes the YD, a cold interlude in Greenland, during which, again after a delay, the Antarctic resumes warming. So there is a seesaw of sorts, although it is quite messy and inprecise, depending – as you say – on your sources. Of course seesawing with delay is consistent with it being from ocean current cycles, rather than atmospheric causation.
It is interesting to speculate that one thing characterising an interglacial is a suspension of bipolar seesawing, and more synchrony between the poles. Then as Tzedakis asserts, the seesaw returns after the interglacial at (or shortly after) glacial inception. Another interesting observation in this Tzedakis paper is that “glacial inception always takes place when obliquity is decreasing and never after the obliquity minimum”. Is it possible that decreasing obliquity somehow throws a wobble into oceanic circulation or exerts some resonant effect on it?
Your point about insolation is important, clearly rising insolation kick-started the interglacial, and since then the decreasing insolation in creases the “potential” for us to drop back to glacial. You also show evidence that the bipolar seesaw is occuring again now – perhaps this is a precursor of the much more violent seesaw which characterises a full resumption of glacial conditions, as per Tzedakis, but its existence now shows that the (oceanic) processes leading to the termination of the Holocene interglacial are already well underway.
BTW I do not exclude a YD bolide impact of some kind, the evidence does suggest this. But as others have pointed out e.g. crosspatch, a YD type excursion seems typical of the start of several, maybe all interglacials, not just the latest one.
@leftturnandre:
Um, I’m not saying it is limited I’m saying it is likely that the Younger Dryas as an impact was most likely strongest and the worst effects were limited to the N. Hemisphere and would have been strongest at the end of the Gulf Stream. Yes, there ought to be effects showing up elsewhere on the planet, but no, I’d not expect them to be as strong (and I’m guessing they would be much much less strong.)
So not “restricted” so much as “90% / 10% or even 80% / 20% split” on the energy distribution.
@Phlogiston:
I called it “leveling off” as the line segment goes to about zero slope. It’s a spike / drop, then a ‘go flat’ for a bit (“leveling off”) then resumes warming. Not some great pronouncement, just saying ‘slope goes to near zero average’ in non-technical terms. And yes, it absolutely happens after a local “peak and drop”; even if a small one.
I’m pretty much settling in on “Ocean Cycles” as the dominant feature of climate; but with the “add on” that some (many?) of those “cycles” and “oscillations” can be driven by a lunar metronome. We’ve got a giant tidal metronome beating on our oceans. It wanders higher and lower as the orbit shifts, and in a cycle that exactly matches the duration of observed cold excursions (D.O. / Bond events) modulo one, the Y.D., where there is a likely large impact “issue”. The 60ish year cycle repeats when 3 lunar cycles of about 18 to 19 years each puts the moon right over the same ocean as the first one, about 60 years prior, and in the same position. (In the intervening 2 cycles it’s over a different ocean, so different tides…) On a 1500 (actually a 1200 / 1800 range with a 1500 average) year span, a different lunar movement repeats so a longer cycle of increasing / decreasing tides. (Metonic vs Saros vs…)
Then, on the 25,000 to 41,000 to 120,000 year scale, the Earth vs Sun position and angles change. As that (Milankovich) cycle progresses, we reach a ‘less stable’ point where those lunar cycles can overpower the N. Pole warming, and we get big oscillations. That “entry to the glacial” bi-polar seesaw ‘returning’…
We are now on the cusp in terms of solar warming 65 N. We’ve poised to go back into the ‘less table’ from not enough sunshine on the N. Pole (though the added summer days in the N.H. will likely keep us out of a glacial for the next few hundred years). BUT, the lunar cycles are syncing up to have several all change at the same time from “warmer” to “colder”. Will it be enough to overcome the added days in summer? Nobody knows.
What’s very clear is that we’re approaching or on the cusp of the next ice age glacial; nothing can stop it, and we have no ability to predict the onset precisely (as it is based on several poorly characterized moving parts). We almost dropped into it during the Little Ice Age, and have a “few hundred years” before that cycle repeats (likely much colder next time…).
My best guess is about 300 years. Then it’s a coin toss for “back to the glacial”. If we make it through that, at about 4000 A.D. we are simply too little insolation up north and the next lunar cool cycle hits. Then it’s all over and we’re in a glacial, if not already…
As I said: That is a GUESS. But one based on a reasonable understanding of the most likely actual mechanisms.
Oh, and as we move to ever lower average insolation, we get ever less stable / warm weather. So the next few hundred years ought to see a return of unstable weather prone to strong excursions…
@Phlogiston
You said:
Between 17000 and 15000 Ya the Antarctic sharply warms while Greenland cools slightly. Then between about 14500 and 13000 Ya Greenland becomes abruptly warmer, although the warming is all at the start in a sharp increase followed by a cooling trend.
The period of 17.5 ka to 14.5 ka is dubbed the mystery interval (Denton et al 2006) because of mixed signals. Was the northern hemisphere delayed in cooling or?
Nope. It’s all a matter of isotope misinterpretation.
http://www.sciencedirect.com/science/article/pii/S0277379106001521
Check also Hubberten et al 2004 (fig 6 page 1339)
http://epic.awi.de/9052/1/Hub2004a.pdf
See that the warming starts at 15,000 radiocarbon years ago but notice that this calibrates to 18000 years ago using the intcal09 calibration table ( http://www.radiocarbon.org/IntCal09%20files/intcal09.14c )
So the Northern hemisphere wasn’t seesawing at all. It’s all about misinterpretation of the isotope signal.
Ref
Denton G.H., Broecker, W.S. and Alley, R.B., 2006: The mystery interval 17.5 to 14.5 kyrs ago, PAGES news, 2: 14-16.
Blame the Sun !
From the collective memory of humanity the Sodom and Gomorrah event is a description of Clovis mishappening. (more recently Asterix people fear of a falling sky š
This kind of event is recursive because the Sun is not only stable as it is also unstable. It will happen again in a short time scale.
The Sun produces and accumulates a tiny fraction of heavy elements. This is a 100% true sentence : the probability of an heavy atom creation is very low but not null and because they accumulate we must decide their fate: They are not reported at the Sun’s surface. Do they sink because they are heavier? NO, because the atom is bathed in a plasma of protons and electrons that is denser than the ionized heavy atoms (it is void between the nucleus and its own electronic cloud). They are clamped together under the surface of the Sun and forming a shell, obstructing the radiation, that periodically surface as sunspots. They go up and release energy and then go down again and accumulate near the equator due to the centrifugal force.
From time to time the belt of matter can not cope anymore with the radiation pressure and we had a YD type event. This is also the origin of the planets of the solar system (that’s why almost all of the angular momentum of SS is way out of the Sun; it is impossible to make a sucessful simulation of the Solar System originated from a collapsing cloud of matter).
This is the first time that this view is written in English language ( in Portuguese at outramargem-alf.blogspot.com under the tag Sol ).