Younger Dryas - likely the result of meteor impact

[jim mcnamara]

Origin and provenance of spherules and magnetic grains at the Younger Dryas boundary
Yingzhe Wu, Mukul Sharma, Malcolm A. LeCompte, Mark N. Demitroff, and Joshua D. Landis
PNAS 2013 ; published ahead of print September 5, 2013, doi:10.1073/pnas.1304059110
From the pnas.org overview:

Significance
This study ties the spherules recovered in Pennsylvania and New Jersey to an impact in Quebec about 12,900 y ago at the onset of Younger Dryas. Our discovery resulted from an exhaustive search that examined the question of whether there is any evidence of extraterrestrial platinum group metals present in the bulk sediments, magnetic grains, and spherules recovered from the Younger Dryas boundary (YDB). We find that the spherules are likely quenched silicate melts produced following the impact at the YDB. The source of spherule osmium, however, is likely terrestrial and not meteorite derived.

The takeaway is that a large meteor impact in Quebec showered a very large area in Northeastern North America with hot debris. The debris is at the exact boundary of the onset of the Younger Dryas. If this impact did not entirely cause the Younger Dryas cooling, it certainly is the most likely major player in the event. (My interpretation).

Mukul Sharma, one of the researchers, said as much in an article earlier:
http://www.theregister.co.uk/2013/0...d_for_triggering_younger_dryas_climate_shift/

 

[Greg Bernhardt]

Interesting, thanks for sharing Jim!

 

[betzalel]

It is astonishing how long it takes to solve holistic scientific problems. The analysis goes off into left field or runs in circles.

There is no formal summary of all of the data and the competing theories related to the problem. Anomalies and paradoxes are ignored (There must be a physical explanation for everything that has happened and will happen.) Theories are not compared to each other. The people writing and reviewing the papers show obvious bias. The system rewards unending paper writing rather than problem solving.

1) Impact as the cause of the burn marks is Extraordinarily Unlike as it Requires Multiple Separate Impacts

An astrophysicist researcher commented on a PBS program that discussed the Younger Dryas comet/meteoroid theory that it is impossible for a single comet or a single meteoroid impact to cause the observed burn marks on two different continents at multi latitudes (nine locations). The observed pattern of nine locations with burn marks on two different continents at multiple latitudes would require multiple impacts from separate comets and/or meteoroids (eight or nine, almost no probability of one object causing multiple burn marks).

(Think of the necessary orbital trajectory of the objects and try to image what trajectory would be required to create the observed pattern of nine locations where there were burn marks.)

The astrophysicist then noted based on the probability of a single impact it is virtually impossible for there to be multiple impacts (eight or nine) in such a short time period.

He also noted that the probability is further reduced as the requirement is for the burn marks with no impact crater which requires special conditions.

2) The Younger Dryas Abrupt Cooling Period Lasted for 1200 years

An impact to the Earth will cool the Earth for a few years, similar to what is observed again and again for a single major eruption. The planet resists forcing changes rather than amplifies forcing changes by an increase or decrease in clouds in the tropics. The cooling due to a major impact will last less than a decade.

3) There are cycles of abrupt climate in the paleo record which have a periodicity of 1470 years which are called Dansgaard-Oeschger cycles and Heinrich cycles. The Heinrich cycles require a very, very strong forcing function, as they are capable of terminating an interglacial period. The Younger Dryas abrupt cooling event is a Heinrich event. What causes the Heinrich events (cycles) and the Dansgaard-Oeschger cycles that happens again and again and again. It is not impacts.

4) There is the largest change in C14 in the Holocene at the Younger Dryas. A massive change in C14 requires either a massive change to the geomagnetic field or a very, very long abrupt change to the sun.

http://www.falw.vu/~renh/pdf/Renssen-etal-QI-2000.pdfhttp://sheridan.geog.kent.edu/geog41066/7-Overpeck.pdf

ABRUPT CHANGE IN EARTH’S CLIMATE SYSTEM Jonathan T. Overpeck and Julia E. Cole

….Abrupt shifts between warm and cold states punctuate the interval between 20 to 75 ka) in the Greenland isotope record, with shifts of 5–15C occurring in decades or less (Figure 1). These alternations were identified in some of the earliest ice core isotopic studies [e.g., (22)] and were replicated and more precisely dated by subsequent work (23). Further analysis of diverse records has distinguished two types of millennial events (13). Dansgaard/Oeschger (D/O) events are alternations between warm (interstadial) and cold (stadial) states that recur approximately every 1500 years, although this rhythm is variable. Heinrich events are intervals of extreme cold contemporaneous with intervals of ice-rafted detritus in the northern North Atlantic (24–26); these recur irregularly on the order of ca. 10,000 years apart and are typically followed by the warmest D/O interstadials.

Both Heinrich and D/O events exhibit clear global impacts. These patterns have been summarized in several studies [e.g., (26, 34)]. Although the pattern of influence appears to differ between these types of anomaly, a clear interpretation of these differences, particularly in terms of distinguishing physical mechanisms, has not been developed. As Hemming (26) notes, different global patterns of impact may simply reflect proxy-specific or site-specific limitations such as sensitivity and response time. In general, however, a cold North Atlantic corresponds with a colder, drier Europe, weaker Asian summer monsoon, saltier northwestern tropical Pacific, drier northern South America, colder/wetter western North America, cooler eastern subtropical Pacific, and warmer South Atlantic and Antarctic. Table 1 summarizes the main impacts of a cold North Atlantic (stadial) on key regions and systems. …..

The 8200-year Climate Eventhttp://www.geo.arizona.edu/palynology/geos462/8200yrevent.htmlhttp://www.esd.ornl.gov/projects/qen/transit.html

Sudden climate transitions during the Quaternary

According to the marine records, the Eemian interglacial (betzalel: Eemain is the name of the last interglacial period) ended with a rapid cooling event about 110,000 years ago (e.g., Imbrie et al., 1984; Martinson et al., 1987), which also shows up in ice cores and pollen records from across Eurasia. From a relatively high resolution core in the North Atlantic. Adkins et al. (1997) suggested that the final cooling event took less than 400 years, and it might have been much more rapid.

The event at 8200 BP is the most striking sudden cooling event during the Holocene, giving widespread cool, dry conditions lasting perhaps 200 years before a rapid return to climates warmer and generally moister than the present. This event is clearly detectable in the Greenland ice cores, where the cooling seems to have been about half-way as severe as the Younger Dryas-to-Holocene difference (Alley et al., 1997; Mayewski et al., 1997). No detailed assessment of the speed of change involved seems to have been made within the literature (though it should be possible to make such assessments from the ice core record), but the short duration of these events at least suggests changes that took only a few decades or less to occur.

The Younger Dryas cold event at about 12,900-11,500 years ago seems to have had the general features of a Heinrich Event, and may in fact be regarded as the most recent of these (Severinghaus et al. 1998). The sudden onset and ending of the Younger Dryas has been studied in particular detail in the ice core and sediment records on land and in the sea (e.g., Bjoerck et al., 1996), and it might be representative of other Heinrich events.

 

[Evo]

IIRC, the younger dryas /meteor event was disproved, we had threads about it.

 

[betzalel]

IIRC, the younger dryas /meteor event was disproved, we had threads about it.

Hello,
The problem of what causes cyclic abrupt climate change and the glacial/interglacial cycle has not been solved. There is the unsolved scientific problem and there is a problem/issue that unsolved scientific problems are not solved.

The analysis and solution of what caused the Younger Dryas is directly connected to the analysis of what causes the glacial/interglacial cycle. Both analyses are going in circles. The 2013 published, Impact Paper is an example to support the assertion the analysis does not converge on solving the scientific problem. There are basic fundamental problem solving techniques that are used in private industry to solve complex holistic problems that are not used in pure science.

The analysis is not converging on finding the physical cause of abrupt cyclic climate change. The issue is not a lack of data. There are piles and piles of observations to solve the problem of what cause cyclic abrupt climate change and what causes the glacial/interglacial cycle. The physical solution to the problem is not included with the list of hypotheses/theories that is being evaluated.

There are three urban legend forcing functions:

1) The assertion that changes in summer insolation at 65N being the cause of the glacial/interglacial cycle is an urban legend. The Younger Dryas abrupt climate change is an example of cyclic abrupt climate change. It occurred during a period when summer insolation at 65N was at maximum. There are other examples in the paleo record of exactly the same phenomenon as the Younger Dryas. There are seven fundamental problems with the orbital changes in solar insolation at 65N which support the assertion that it is an urban legend. This disproved theory is included in every paleo climate textbook.

2) The assertion that an interruption to the North Atlantic drift current as being a possible cause for cyclic abrupt climate change is an urban legend. This disproved theory is included in every paleo climate textbook and every paper that discusses the Younger Dryas event.

http://www.atmos.washington.edu/~david/Gulf.pdf

Is the Gulf Stream responsible for Europe’s mild winters?

By R. SEAGER, D. S. BATTISTI, J. YIN, N. GORDON, N. NAIK, A. C. CLEMENTand M. A. CANE

...In conclusion, while OHT warms winters on both sides of the North Atlantic Ocean by a few degC, the much larger temperature difference across the ocean, and that between the maritime areas of north-western Europe and western North America, are explained by the interaction between the atmospheric circulation and seasonal storage and release of heat by the ocean. Stationary waves greatly strengthen the temperature contrast across the North Atlantic and are themselves heavily influenced by the net effect of orography. In contrast, transport of heat by the ocean has a minor influence on the wintertime zonal asymmetries of temperature. Even in the zonal mean, OHT has a small effect compared to those of seasonal heat storage and release by the ocean and atmospheric heat transport. In retrospect these conclusions may seem obvious, but we are unaware of any published explanation of why winters in western Europe are mild that does not invoke poleward heat transport by the ocean as an important influence that augments its maritime climate.

http://www.americanscientist.org/issues/id.999,y.0,no.,content.true,page.1,css.print/issue.aspx

The Source of Europe's Mild Climate
The notion that the Gulf Stream is responsible for keeping Europe anomalously warm turns out to be a myth

3) Comet/asteroid impact.

It is a fact that abrupt climate change is cyclic. The Heinrich events and the lesser Dansgaard-Oeschger cyclic warming and cooling occur along the same 1470 year series which supports the assertion that they both have the same cause. Impacts are not cyclical. Regardless an impact will cause the planet to cool for less than a decade, not 1200 years.http://www.pik-potsdam.de/~stefan/Publications/Journals/rahmstorf_grl_2003.pdf

Timing of abrupt climate change: A precise clock by Stefan Rahmstorf

Many paleoclimatic data reveal an approx. 1,500 year cyclicity of unknown origin. A crucial question is how stable and regular this cycle is. An analysis of the GISP2 ice core record from Greenland reveals that abrupt climate events appear to be paced by a 1,470-year cycle with a period that is probably stable to within a few percent; with 95% confidence the period is maintained to better than 12% over at least 23 cycles. This highly precise clock points to an origin outside the Earth system; oscillatory modes within the Earth system can be expected to be far more irregular in period.

The burn marks are a clue to what causes abrupt geomagnetic excursions. What caused the high temperature burn marks? It is not an impact. There needs to be a physical explanation for the burn marks.

There is an abrupt change to the geomagnetic field (which causes the largest increase in C14 in Holocene record) that correlates with the Younger Dryas abrupt cooling event.

The paleo record shows the geomagnetic field tilt is cyclically abruptly changing by 10 to 15 degrees. The north pole drift velocity increased, in the mid 1990s from the 15 km/yr to 55 km/yr. The geomagnetic field intensity drop also in the mid 1990's has increased from the 5%/century to 5%/decade.

There is a current paradox that requires a physical cause. The geomagnetic field is currently dropping ten times faster than possible for a change in the liquid core. A magnetic excursion will cause the planet to cool for 1200 years. An impact will cause the planet to cool for less than decade, not 1200 years.This is a link to the 2013 paper.

http://www.pnas.org/content/110/32/12917.full.pdf

Large Pt anomaly in the Greenland ice core points to a cataclysm at the onset of Younger Dryas

The Younger Dryas (YD), a millennium-long cooling period amid postglacial warming well documented in the Greenland ice cores (e.g., refs. 1, 2), is thought to result from an abrupt change in atmospheric and oceanic circulation (3) (betzalel, the hypothesis that a complete stoppage of the Gulf stream could cause what is observed is an urban legend). Whether such a change was caused by a catastrophic event or it is an integral, although still poorly understood, feature of the deglaciation process remains unclear (4). The impact hypothesis (11), once declared dead (12, 13), recently gained new support from the discovery of siliceous scoria-like objects (SLOs) with global distribution, which provide strong evidence for processing at high temperatures and pressures consistent with a cosmic impact (14).

 

[NileQueen]

betzalel, What burn marks are you talking about?

 

[Evo]

Here are the opposing hypotheses.

According to one hypothesis, a cometary airburst triggered massive wildfires, which caused the climate to cool. Many scientists have rejected this hypothesis, citing lack of sufficient evidence, in favor of others. The most widely accepted one says that during the deglaciation process, fresh water from the proglacial lake Agassiz discharged into the Arctic Ocean, altering ocean currents.

However, Petaev's team says that geomorphological and chronological data do not support this. They claim that evidence for another hypothesis, that the eruption of the Laacher See volcano caused a volcanic winter in the northern hemisphere, is also lacking.

Now, the researchers claim to have uncovered evidence of a cosmic impact at the Younger Dryas boundary. When examining samples from Greenland Ice Sheet Project 2 (GISP2), they found that platinum concentration increased by about 100 times approximately 12,900 years ago.

Platinum/iridium and platinum/aluminum ratios were very high, indicating that the platinum probably did not have a terrestrial source. While most volcanic rocks have high Pt/Ir ratios, their Pt/Al ratios are low. Mantle rocks have low levels of aluminum, but their Pt/Ir ratios are much lower than that measured in the ice core.

Read more at: http://phys.org/news/2013-08-evidence-cosmic-impact-younger-dryas.html#jCp

An international team of scientists led by researchers at the University of Hawaii at Manoa have found no evidence supporting an extraterrestrial impact event at the onset of the Younger Dryas ~13000 years ago.

This cooling period is generally considered to be the result of the complex global climate system, possibly spurred on by a reduction or slowdown of the thermohaline circulation in North America. This paradigm was challenged two years ago by a group of researchers that reported finding high iridium concentrations in terrestrial sediments dated during this time period, which led them to theorise that an impact event was instead the instigator of this climate shift.

A team led by François Paquay, a Doctoral graduate student in the Department of Geology and Geophysics at the University of Hawaii at Manoa (UHM) decided to also investigate this theory, to add more evidence to what they considered a conceptually appealing theory. However, not only were they unable to replicate the results found by the other researchers, but additional lines of evidence failed to support an impact theory for the onset of the Younger Dryas. Their results will be published in the December 7th early online edition of the prestigious journal the Proceedings of the National Academy of Sciences.

Read more at: http://phys.org/news/2009-12-absence-evidence-meteorite-impact-event.html#jCp

 

[NileQueen]

Evo, there are many more papers in favor of the Firestone et al. 2007 impact hypothesis.

Regarding citation #2, read Lecompte et al 2012 for why at least one other researcher (Todd Surovell) could not find the evidence: improper methodology.

LeCompte, M. A., Goodyear, A. C., Demitroff, M. N., Batchelor, D., Vogel, E. K., Mooney, C., ... & Seidel, A. W. (2012). Independent evaluation of conflicting microspherule results from different investigations of the Younger Dryas impact hypothesis. Proceedings of the National Academy of Sciences, 109(44), E2960-E2969.

Betzalel, these are not "burn marks". They are referred to by Haynes 2008 as "black mats" although some sites are not black.

The Gothenburg Magnetic excursion (Nils Axel Morner) has been debated, as apparently it could not be reproduced. It may be valid, but I am not sure
the excursion and fire are linked. How do you explain the Pt spike in the ice cores (Petaev et al 2013) with your hypothesis of an electrical/geomagnetic phenomenon at YDB?

 

[Evo]

Evo, there are many more papers in favor of the Firestone et al. 2007 impact hypothesis.

Yes, but there are many others that show evidence to the contrary. I admit I do not know who/what to believe. I do trust your judgement on these issues, so if you are convinced of the Firestone impact hypothesis, I will re-read the other studies with more scrutiny.

Greenland ice cores also show ammonium (NH4+) increases during the Tunguska event and the Younger Dryas (http://geology.gsapubs.org/content/38/4/383.short?rss=1&ssource=mfr#F1). While biomass burning is implicated for the Younger Dryas increase (e.g., http://geology.gsapubs.org/content/38/4/383.short?rss=1&ssource=mfr#ref-10), the amount of burning during the Tunguska event is too small to account for the ammonium increase of >200 ppb (http://geology.gsapubs.org/content/38/4/383.short?rss=1&ssource=mfr#ref-19). Another alternative, involving direct ammonium deposition from the bolide, still fails to account for the observed Tunguska increase. The authors thus suggest a third mechanism called the Haber process that could account for both the Younger Dryas and Tunguska increases, in which, under high pressure, nitrogen and hydrogen can form ammonia. For the Tunguska increase, a potential impact with permafrost could provide the hydrogen, whereas the Laurentide Ice Sheet itself might be the hydrogen source for the Younger Dryas impact.

The Melott et al. study thus lays out a test for the occurrence of a Younger Dryas bolide impact, constrained by observations of the recent Tunguska impact. Their estimates, however, for the increases in nitrate and ammonium associated with a Younger Dryas–size comet are orders of magnitude larger than observed in the Summit Greenland ice core records; the Younger Dryas nitrate and ammonium increases are at most just half of the Tunguska increase. Likewise, the anomalies noted at the start of the Younger Dryas appear to be non-unique in the highest-resolution records (http://geology.gsapubs.org/content/38/4/383.short?rss=1&ssource=mfr#F1). This may be due to the ice core sample resolution. The GISP2 ∼3.5 yr sample resolution could potentially under-sample a nitrate or ammonium increase (http://geology.gsapubs.org/content/38/4/383.short?rss=1&ssource=mfr#ref-18) because both compounds have atmospheric residence times of a few years. As Melott et al. note, higher-resolution sampling from the Greenland ice cores could determine if large (i.e., orders of magnitude larger than the Tunguska event) increases in nitrate and ammonium occurred at the start of the Younger Dryas.

continued...

http://geology.gsapubs.org/content/38/4/383.short?rss=1&ssource=mfr

 

[NileQueen]

So...Evo, nitrate can be a combustion marker in ice cores, but it can also be from nitric acid rain following an extraterrestrial event (nitrates form
from the dissociation of N2 in the atmosphere and O3 in the stratosphere; these nitrates rain out as nitric acid rain (Prinn and Fegley 1987)).
Turns out that we could determine whether the nitrates were from biomass burning or shockwave nitrates by analyzing the Oxygen isotopes
in the NO3 (nitrate). The ozone layer is enriched in 17O, and nitrates formed from that source would also be enriched in 17O (Hastings et al. 2013).
There are other markers that can be used for biomass burning. These include acetate, formate, ammonium, oxalate and levoglucosan.

 

[betzalel]

Here are the opposing hypotheses.

Read more at: http://phys.org/news/2013-08-evidence-cosmic-impact-younger-dryas.html#jCp

In reply to:

This cooling period is generally considered to be the result of the complex global climate system, possibly spurred on by a reduction or slowdown of the thermohaline circulation in North America.

The melt pulse occurred a 1000 years before the Younger Dryas event. Regardless, complete stoppage of the North Atlantic drift current will only result in winter cooling of Europe of a few degrees.

http://www.atmos.washington.edu/~david/Gulf.pdf

Is the Gulf Stream responsible for Europe’s mild winters?

By R. SEAGER1¤, D. S. BATTISTI2, J. YIN2, N. GORDON1, N. NAIK1, A. C. CLEMENT3 and M. A. CANE1

Is the transport of heat northward by the Gulf Stream and North Atlantic Drift, and its subsequent release into the midlatitude westerlies, the reason why Europe’s winters are so much milder than those of eastern North America and other places at the same latitude? Here, it is shown that the principal cause of this temperature difference is advection by the mean winds. South-westerlies bring warm maritime air into Europe and north westerlies bring frigid continental air into north-eastern North America. Further, analysis of the ocean surface heat budget shows that the majority of the heat released during winter from the ocean to the atmosphere is accounted for by the seasonal release of heat previously absorbed and not by ocean heat-convergence. Therefore, the existence of the winter temperature contrast between western Europe and eastern North America does not require a dynamical ocean.

Two experiments with an atmospheric general-circulation model coupled to an ocean mixed layer confirm this conclusion. The difference in winter temperatures across the North Atlantic, and the difference between western Europe and western North America, is essentially the same in these models whether or not the movement of heat by the ocean is accounted for. In an additional experiment with no mountains, the flow across the ocean is more zonal, western Europe is cooled, the trough east of the Rockies is weakened and the cold of north-eastern North America is ameliorated. In all experiments the west coast of Europe is warmer than the west coast of North America at the same latitude whether or not ocean heat transport is accounted for. In summary the deviations from zonal symmetry of winter temperatures in the northern hemisphere are fundamentally caused by the atmospheric circulation interacting with the oceanic mixed layer.

Secondly there is no thermal haline conveyor. Wally Broeker suggested there was a thermal haline conveyor based on his assumption not based on observations and that urban legend took off and is repeated everywhere.

http://www.sciencedaily.com/releases/2009/05/090513130942.htm

Cold Water Ocean Circulation Doesn't Work As Expected

The familiar model of Atlantic ocean currents that shows a discrete "conveyor belt" of deep, cold water flowing southward from the Labrador Sea is probably all wet.

A 50-year-old model of ocean currents had shown this southbound subsurface flow of cold water forming a continuous loop with the familiar northbound flow of warm water on the surface, called the Gulf Stream.

"Everybody always thought this deep flow operated like a conveyor belt, but what we are saying is that concept doesn't hold anymore," said Duke oceanographer Susan Lozier. "So it's going to be more difficult to measure these climate change signals in the deep ocean.

Studies led by Lozier and other researchers had previously suggested cold northern waters might follow such "interior pathways" rather than the conveyor belt in route to subtropical regions of the North Atlantic. But "these float tracks offer the first evidence of the dominance of this pathway compared to the DWBC."

But only 8 percent of the RAFOS floats' followed the conveyor belt of the Deep Western Boundary Current, according to the Nature report. About 75 percent of them "escaped" that coast-hugging deep underwater pathway and instead drifted into the open ocean by the time they rounded the southern tail of the Grand Banks.

Eight percent "is a remarkably low number in light of the expectation that the DWBC is the dominant pathway for Labrador Sea Water," the researchers wrote.

 

[NileQueen]

Betzalel, what are these "ten locations"?

YD does not appear to have been cold in the southeastern US.

Research has been conducted on the sun as a possible factor for Younger Dryas abrupt changes. Renssen et al. 2000 in Quaternary International.

Reduced solar activity as a trigger for the start of the Younger Dryas?

• Hans Renssen
• Bas van Geel
• Johannes van der Plicht
• Michel Magny

http://www.sciencedirect.com/science/article/pii/S1040618200000604

 

[NileQueen]

Re: "Ten locations" that got very hot, see Haynes 2008 for a report on so called black mats in the U.S.

http://www.pnas.org/content/105/18/6520.short

There are also black mats in Venezuela, in The Netherlands, Belgium and Germany. They may be elsewhere as well.

 

[NileQueen]

To see a presentation on these charcoal-rich layers in The NL and BE (called Usselo horizons), go here

https://www.researchgate.net/profile/Joanne_Ballard and look at Usselo Horizon presentation
We collected samples in 2011.

 

[NileQueen]

Betzalel, the hypothesized impactor could have broken into many pieces. Also the shockwave generates heat.
The geomagnetic research is very important though.

 

[Chronos]

Is it not feasible the younger dryas was triggered by a comet that fragemented in the atmosphere? Apologies, I just noticed NileQueen is suggesting the same possibility.

 

[betzalel]

Betzalel, what are these "ten locations"?

YD does not appear to have been cold in the southeastern US.

Research has been conducted on the sun as a possible factor for Younger Dryas abrupt changes. Renssen et al. 2000 in Quaternary International.

Reduced solar activity as a trigger for the start of the Younger Dryas?

• Hans Renssen
• Bas van Geel
• Johannes van der Plicht
• Michel Magny

http://www.sciencedirect.com/science/article/pii/S1040618200000604

There are ten burn mark sites (nine in the North America and one in Europe).

http://www.pnas.org/content/suppl/2007/09/20/0706977104.DC1

It is not possible for a single object to 'break up' to cause the burn marks. Look at the locations where the burn marks were found.

Fig. 9. Research sites with calibrated YDB ages, including Lommel, Belgium, shown in Inset. High-Ir sites are shown in green. For the Bays, three of five sediment analyses revealed detectable Ir values, although radiocarbon ages of the Bays are inconsistent. Sediments from sites with no detectable Ir values (<0.5 ppb) are shown in brown. Sites with black mats are marked with inverted triangles. The approximate extent of the North American ice sheets at 12.9 ka is shown in blue-green, which is consistent with our observations that all sites were ice-free at the time of the YD event.

As noted an impact will cool the Earth for less than a decade, the same as a major eruption.

The Younger Dryas abrupt cooling event was for 1200 years. An impact cannot cause the burn marks and an impact cannot cause cooling for 1200 years.

Lastly the cooling events are cyclic not a one of event.

http://www.pik-potsdam.de/~stefan/Publications/Journals/rahmstorf_grl_2003.pdf

Timing of abrupt climate change: A precise clock by Stefan Rahmstorf
Many paleoclimatic data reveal a approx. 1,500 year cyclicity of unknown origin. A crucial question is how stable and regular this cycle is. An analysis of the GISP2 ice core record from Greenland reveals that abrupt climate events appear to be paced by a 1,470-year cycle with a period that is probably stable to within a few percent; with 95% confidence the period is maintained to better than 12% over at least 23 cycles. This highly precise clock points to an origin outside the Earth system; oscillatory modes within the Earth system can be expected to be far more irregular in period.

http://www.geo.arizona.edu/palynology/geos462/8200yrevent.html

Abrupt tropical cooling ~8,000 years ago

We drilled a sequence of exceptionally large, well-preserved Porites corals within an uplifted palaeo-reef in Alor, Indonesia, with Th-230 ages spanning the period 8400 to 7600 calendar years before present (Figure 2). The corals lie within the Western Pacific Warm Pool, which at present has the highest mean annual temperature in the world's ocean. Measurements of coral Sr/Ca and oxygen 18 isotopes at 5-year sampling increments for five of the fossil corals (310 annual growth increments) have yielded a semi-continuous record spanning the 8.2 ka event. The measurements (Figure 2) show that sea-surface temperatures were essentially the same as today from 8400 to 8100 years ago, followed by an abrupt ~3C cooling over a period of ~100 years, reaching a minimum ~8000 years ago. The cooling calculated from coral oxygen 18 isotopes is similar to that derived from Sr/Ca. The exact timing of the termination of the cooling event is not yet known, but a coral dated as 7600 years shows sea-surface temperatures similar to those of today.

http://www.esd.ornl.gov/projects/qen/transit.html

Sudden climate transitions during the Quaternary

Abstract

The time span of the past few million years has been punctuated by many rapid climate transitions, most of them on time scales of centuries to decades or even less. The most detailed information is available for the Younger Dryas-to-Holocene stepwise change around 11,500 years ago, which seems to have occurred over a few decades. The speed of this change is probably representative of similar but less well-studied climate transitions during the last few hundred thousand years. These include sudden cold events (Heinrich events/stadials), warm events (Interstadials) and the beginning and ending of long warm phases, such as the Eemian interglacial. Detailed analysis of terrestrial and marine records of climate change will, however, be necessary before we can say confidently on what timescale these events occurred; they almost certainly did not take longer than a few centuries.

Various mechanisms, involving changes in ocean circulation, changes in atmospheric concentrations of greenhouse gases or haze particles, and changes in snow and ice cover, have been invoked to explain these sudden regional and global transitions. We do not know whether such changes could occur in the near future as a result of human effects on climate. interglacial, with cold and dry phases occurring on a 1500-year cycle, and with climate transitions on a decade-to-century timescale. In the past few centuries, smaller transitions (such as the ending of the Little Ice Age at about 1650 AD) probably occurred over only a few decades at most. All the evidence indicates that most long-term climate change occurs in sudden jumps rather than incremental changes.

 

[NileQueen]

Betzalel, there are not "ten burn sites". There are AT LEAST 97.
http://www.pnas.org/content/105/18/6520.full

There can be a fireball from the shockwave heating of the atmosphere; look at literature on the K/T (now K/Pg) impact.
e.g. http://www.ucmp.berkeley.edu/education/events/cowen1b.html
..."Once Chicxulub was identified, it became possible to calculate that shocked quartz had been launched into a high-angle spray from the impact. This first hot fireball blew vaporized and molten debris (including glass spherules and iridium) high above the atmosphere to be deposited last and globally as it slowly drifted downward. The larger fragments, solid and molten, were blasted outward at lower angles, but not very far, and were deposited first and locally (about 15 minutes travel time to Colorado!). At the same time, smaller fragments, including shocked quartz, were blown upward between the hot fireball and the larger fragments, and were deposited second and regionally (about 30 minutes to reach Colorado). The impact energy, for comparison with hydrogen bomb blasts, was around 100 million megatons."

The YD was likely very wet at the beginning from ponding of water (lack of evapotranspiration), and then very dry due to increased wind.
There was more sea ice in the North Atlantic (see for instance, Brauer et al. 2008, Increased windiness...) less or almost no evaporation from the North Atlantic, and less deposition of snow
on the Greenland ice sheet.