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 researcher’s 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 Sagan’s “Extraordinary claims require extraordinary evidence” comes to mind with regard to the Younger Dryas claims but I have to admit, based on the global warming “consensus,” 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 Alvarez’s 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) didn’t 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 “deniers.”
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 won’t 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 “air blasts,” 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. Let’s 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 didn’t 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.
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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 “air blasts,” 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 ““Extraordinary claims require extraordinary evidence” 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 ““Extraordinary claims require extraordinary evidence” 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. ”
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 🙂
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 planet’s 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 – 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.
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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 ‘iron’ 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 “no case to answer” with the Younger Dryas (YD). Glacial periods – 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 – in fig. 2 – first a warming in the southern ocean about 16 kYa, then the “Antarctic cold reversal”, 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 world’s 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