Guest shoot-down by David Middleton
Preface
In my previous two posts on uniformitarian impact craters, we examined the pitfalls of drawing cartoons on Google Earth images without ever looking at the geology and how the Carolina Bays are as antithetical to impact features as any dents in the ground possibly could be. Judging by some of the comments, this seems to have given some readers the impression that I am an opponent of the Younger Dryas Impact Hypothesis (YDIH), despite repeatedly stating that I find some of the evidence compelling.
For the record, I have not drawn any conclusions about whether or not a significant impact event or events may have occurred coincident with the Younger Dryas glacial stadial. However, I do have firmly negative opinions about science fiction-derived and sloppy science-derived evidence for the YDIH and other similarly derived impact hypotheses.
This will be another long post. If the subject matter doesn’t interest you… Sorry.
This post will deal primarily with one issue in the latest YDIH paper (Wolbach et al,. 2018): A purported increase in atmospheric CO2 during the Younger Dryas as evidence of “extraordinary biomass-burning.” While I will discuss other aspects of the Younger Dryas and YDIH, my main focus will be on atmospheric CO2 and CH4.
Real Clear Science
I have the greatest respect for Ross Pomeroy, Chief Editor of RealClearScience (RCS), as I do for RCS’s founding editor Alex Berezow. Mr. Pomeroy recently wrote a very thoughtful article about Wolbach et al., 2018:
A Cometary Upheaval in the History of North America
By Ross Pomeroy
May 10, 2018
Around 12,900 years ago, Earth’s climate abruptly changed, but the upheaval was particularly felt in North America. Over the span of just a decade, temperatures fell between 3.6 and 10.8 degrees Fahrenheit on average. Glaciers which had been gradually receding through Canada reversed course and crept southward. The air dried, and droughts became frequent. Megafauna like mammoths, camels, and giant bears couldn’t adapt to the sudden changes and died out in droves, their extinction abetted by hungry humans on the hunt.
[…]
Dozens, and perhaps hundreds, of scientists from all across the world now ascribe to the notion that some sort of cometary impact triggered the Younger Dryas cooling and extinctions.
[…]
But critics have countered their claims every step of the way, questioning the dating techniques used, disputing the origin of the nanodiamonds, and pointing out that no large impact craters linked to the Younger Dryas have yet been found. Their fierce skepticism is justified. Supporters of a Younger Dryas impact hypothesis are making a bold claim. It is their responsibility to back it up.
And back it up they have. In the past few years, researchers have published dozens of peer-reviewed scientific papers to support a comet impact. Just a few months ago, they released their most exhaustive research yet – two studies of 129 lake cores taken from around the world showing that 12,900 years ago there was a spike in sediment charcoal levels, a clear sign of burning on a massive scale. Moreover, ice cores clearly indicate a ten percent spike in global carbon dioxide levels at the same time! It seems something cataclysmic happened just before the Younger Dryas that sent all sorts of carbon into the atmosphere.
[…]
While scientists on each side of this issue have stood opposed, debating for their preferred theories, they have been counterintuitively working together. Every point and counterpoint has forced the other side to refine their ideas and search for new evidence. Indeed if the impact hypothesis does finally win out, it will take its place as the leading theory largely thanks to its most ardent critics.
This is scientific debate at its best.
I agree wholeheartedly with Mr. Pomeroy here:
Indeed if the impact hypothesis does finally win out, it will take its place as the leading theory largely thanks to its most ardent critics.
Genuine scientific debate is good for science. It strengthens valid hypotheses. However, as Holliday et al., 2016 demonstrated, the YDIH has a long way to go.
The Younger Dryas Impact Hypothesis (YDIH) states that North America was devastated by some sort of extraterrestrial event ~12,800 calendar years before present. Two fundamental questions persist in the debate over the YDIH: Can the results of analyses for purported impact indicators be reproduced? And are the indicators unique to the lower YD boundary (YDB), i.e., ~12.8k cal yrs BP? A test reported here presents the results of analyses that address these questions. Two different labs analyzed identical splits of samples collected at, above, and below the ~12.8ka zone at the Lubbock Lake archaeological site (LL) in northwest Texas.
[…]
The results of analyses of blind samples collected at the Lubbock Lake site to test the YD impact hypothesis produced no evidence of an extraterrestrial impact at the YDB. The results from one lab show no peak in magnetic grains nor in magnetic microspheres but data from another lab shows significantly elevated levels of purported impact indicators (magnetic microspherules and nanodiamonds) at <11,500 cal yrs BP, well over 1000 years later than the YDB. These results are consistent with a growing body of data that shows that claimed impact indicators are found in deposits both older and younger than the YDB.
[…]
To move forward and better understand what happened at the YDB and also to understand the meaning of purported impact markers, stratigraphic sections with continuous records of sedimentation through the late Pleistocene and Holocene must be sampled throughout at close intervals and dated using high precision methods. To date, only Bement et al [43] report such an approach and their data show peaks in possible impact indicators above and below the YDB. Further, agreed upon criteria must be established for microspherule identification; otherwise counts of spheres are pointless. Complete stratigraphic descriptions of sampled sections also are needed, indicating sediment lithologies, weathering zones, soil morphology, and erosional unconformities. Few are available from among the dozens of sites with claimed impact proxies but are critical for evaluating the depositional context of impact proxies and the interpretation of numerical dates.
The YDIH needs a lot more uniformitarian geology (AKA science) before it will be widely accepted as anything more than a novelty. Although there does seem to be a growing body of evidence to support a platinum group elements (PGE) anomaly:
In addition, the discoveries by Dr. Chris Moore and his colleagues could provide support for some scientists’ claims that a large number of Paleo-Indians from the Clovis culture also died off around that time because of a comet strike.
“It may have been an impact without any impact, but my suspicion is that it probably did have an effect because it is coincident with a major ecological calamity,” said Moore, outreach coordinator for the Savannah River Archeological Research Program, which is based at the Savannah River Site.
Overhunting of megafauna by humans and natural changes in the climate and the environment also could have been factors, he added.
“As things usually are, it probably was a combination of events,” Moore said. “The debate has raged in paleoanthropology and archaeology. The comet thing is sort of a new twist on it, and some scientists absolutely do not buy it.”
Moore’s team wrote a paper about its work that was published by Scientific Reports earlier this year.
In 2013, researchers from Harvard University revealed that they had detected higher-than-normal concentrations of platinum in ice core samples from Greenland that coincided with the start of Younger Dryas.
The scientists said the likely source of the precious metal was a “sub-kilometer iron meteorite.”
Moore and his colleagues wanted to see if they could find the same platinum anomalies in sediment samples from other places.
“Platinum is rare in the Earth’s crust, but it’s common in asteroids and comets,” Moore said. “The only way it could have gotten into the ice was through atmospheric input, which means it fell out of the atmosphere.”
Moore’s team analyzed sediment samples that were about the same age as the Greenland ice core samples from 11 different sites in the United States.
One of the locations was on Santa Rosa Island off the coast of California. Five were in South Carolina, two were in North Carolina and there was one each in Arizona, New Mexico and Ohio.
Nearly all of the sediment samples contained abnormally high levels of platinum.
One of Dr. Moore’s recent publications fairly conclusively demonstrated that the Carolina Bays were not impact features. Other evidence for the YDIH does not constitute evidence that the Carolina Bays are impact features… And the Carolina Bays not being impact features doesn’t shoot down the YDIH. Dr. Moore clearly has a favorable view of the YDIH despite delivering a clean kill to the notion that the Carolina Bays are impact features. If the YDIH is substantially confirmed, it will be through science and scientific debate, not science fiction and cartoons.
While I generally agreed with Mr. Pomeroy’s article, this sentence set my internal alarm bell off:
Moreover, ice cores clearly indicate a ten percent spike in global carbon dioxide levels at the same time!
Having read dozens, if not hundreds, of papers on ice core and plant stomata-derived CO2 histories of the Late Pleistocene and Holocene over the past decade, this statement didn’t sound reasonable.
A Little Background on the Younger Dryas glacial stadial
The Younger Dryas is also known as Glacial Stadial 1 (GS-1). Glacial stadials are the cold phases of glacial stages, some are referred to as Heinrich events. Interstadials (AKA Dansgaard-Oeshger events) are the warm phases of glacial stages. Some interstadials of the most recent Pleistocene glacial stage warmed to nearly interglacial temperatures.
As Late Pleistocene glacial stadials go, the Younger Dryas was not particularly anomalous. If there was a climatology anomaly, it was the warmth of the preceding Bølling-Allerød interstadial (sometimes subdivided).
Late Quaternary Extinctions
While the Younger Dryas and the transition from the last Pleistocene glacial stage to the current interglacial stage (the Holocene) may have been unremarkable from a climatology perspective, about 90 genera of megafauna (mammals weighing at least 44 kg) became extinct during the transition from the Pleistocene to the Holocene (Late Quaternary). While not classified as a mass extinction event, the Late Quaternary extinctions were significant and have been difficult to explain.
The Late Pleistocene-Early Holocene megafauna extinctions took place over 10’s of thousands of years at different times on different continents (Koch & Barnosky, 2006).
“Australia lost 14 of its 16 genera of Pleistocene mammalian megafauna along with
all megafaunal reptiles” (Koch & Barnosky, 2006). By 40,000 years ago, Australia had already lost more than 90% its larger species (Prideaux et al., 2010).
North American (Rancholabrean) extinctions appear to have occurred much later and possibly in at least two phases. While 16 of 35 Rancholabrean extinctions took place during the terminal Pleistocene (~2,000 yr period coincident with the Younger Dryas, the other 19 genera disappeared from the North American fossil record thousands of years earlier (Faith & Surovell, 2009).
Disagreement over the chronology of North American late Pleistocene extinctions stems largely from an incomplete fossil record. Of the 35 genera to disappear from North America, only 16 can be shown to have survived to between 12,000 and 10,000 radiocarbon years B.P. Those 16 genera known from the terminal Pleistocene have been observed to be better represented in the fossil record than those that are not (8, 18, 22). This raises the possibility that the remaining 19 genera have not been dated to the terminal Pleistocene because of their rarity in the fossil record (27). Terminal Pleistocene dates also possibly are lacking for some genera because they did not survive to that time. If so, then this would imply a more complex causality than that supposed by extinction hypotheses requiring a high degree of simultaneity (e.g., overkill or extraterrestrial impact).
2,000 years is a geological blink of the eye. Something catastrophic may have happened in North America during the terminal Pleistocene. This was also when the Folsom culture replaced the Clovis culture. A bolide is certainly a possibility.
So… This takes us to Wolbach et al., 2018.
Extraordinary Biomass-Burning… Maybe, Maybe Not
Extraordinary Biomass-Burning Episode and Impact Winter Triggered by the Younger Dryas Cosmic Impact ∼12,800 Years Ago.
1. Ice Cores and Glaciers
ABSTRACT
The Younger Dryas boundary (YDB) cosmic-impact hypothesis is based on considerable evidence that Earth collided with fragments of a disintegrating ≥100-km-diameter comet, the remnants of which persist within the inner solar system ∼12,800 y later. Evidence suggests that the YDB cosmic impact triggered an “impact winter” and the subsequent Younger Dryas (YD) climate episode, biomass burning, late Pleistocene megafaunal extinctions, and human cultural shifts and population declines. The cosmic impact deposited anomalously high concentrations of platinum over much of the Northern Hemisphere, as recorded at 26 YDB sites at the YD onset, including the Greenland Ice Sheet Project 2 ice core, in which platinum deposition spans ∼21 y (∼12,836–12,815 cal BP). The YD onset also exhibits increased dust concentrations, synchronous with the onset of a remarkably high peak in ammonium, a biomass-burning aerosol. In four ice-core sequences from Greenland, Antarctica, and Russia, similar anomalous peaks in other combustion aerosols occur, including nitrate, oxalate, acetate, and formate, reflecting one of the largest biomass-burning episodes in more than 120,000 y. In support of widespread wildfires, the perturbations in CO2 records from Taylor Glacier, Antarctica, suggest that biomass burning at the YD onset may have consumed ∼10 million km2 , or ∼9% of Earth’s terrestrial biomass. The ice record is consistent with YDB impact theory that extensive impact-related biomass burning triggered the abrupt onset of an impact winter, which led, through climatic feedbacks, to the anomalous YD climate episode.
The Taylor Glacier data are listed as Basuka et al., 2016 in the NOAA paleoclimatology library. Brook et al., 2015 was one of several papers produced as a result of this NSF grant. The full text of Basuka et al., 2016 is available from PNAS:
We extracted atmospheric gases from large (400–500 g) samples taken from surface outcrops of ancient ice at Taylor Glacier, Antarctica, at an average temporal resolution of 165 y between 20 and 10 ka, and subcentury resolution during rapid change events.
[…]
A recent high-resolution record from the West Antarctic Ice Sheet (WAIS) Divide ice core demonstrated that rapid increases in CO2 of about 12 ppm at both the onset of the BA (14.6 ka) and end of the YD (11.5 ka) occurred exactly coincident with abrupt increases in CH4 and Northern Hemisphere (NH) temperature (13).
A resolution of 165 years means that CO2 shifts lasting less than 165 years cannot be resolved. They note that the higher resolution WAIS Divide core puts the CO2 spikes at the onset of the Bølling-Allerød interstadial and termination of the Younger Dryas stadial, citing Marcott et al., 2014…
The WDC methane record shows in detail the abrupt changes at the onset of the Bølling– Allerød and Younger Dryas stadials and the start of the Holocene. We observe a smaller, but prominent, methane excursion at 16.3 kyr ago not previously reported from other records (Fig. 1). Our record also resolves the beginning of the deglacial methane rise at 17.8 kyr ago (Extended Data Table 1).
The WDC CO2 record demonstrates that CO2 varied in three distinct modes during the deglaciation. The first mode is relatively gradual change (,10 p.p.m. kyr21): such changes in CO2 began at 18.1 and 13.0 kyr ago and were broadly coincident with a reduction in the strength of the Atlantic meridional overturning circulation (AMOC; Fig. 2i), a cold North Atlantic2 and warming in the Southern Hemisphere2. The second mode is rapid increase: 10–15 p.p.m. increases in CO2 occurred in three short (100–200 yr) intervals at 16.3, 14.8 and 11.7 kyr ago, the latter two at times of rapid resumption of the AMOC and warming in the Northern Hemisphere. The rapid changes at 14.8 and 11.7 kyr ago were first noted at EDC9,14, but the magnitude, duration and timing are now more fully resolved because of the unique site conditions at WDC.
The highest resolution Antarctic ice cores covering the Younger Dryas are the WAIS Divide cores. This core clearly demonstrates abrupt spikes in atmospheric CO2 at the onset of the Bølling-Allerød interstadial and the termination of the Younger Dryas stadial. These spikes punctuate the secular rise from the last glacial maximum (LGM) to the Holocene. WDC also clearly demonstrates a sharp drop in CH4 during the Younger Dryas.
Furthermore, the Antarctic equivalent of the Younger Dryas cooling event (Antarctic Cold Reversal) preceded the Younger Dryas by about 1,000 years. Antarctica was warming throughout the Younger Dryas. The rise in atmospheric CO2 in Antarctic ice cores during the Younger Dryas is consistent with the secular rise in CO2 during deglaciation, most likely due to warming of the southern oceans.
Some time ago CO2 chronologies from Greenland ice cores were cast aside because they consistently indicated higher and more variable CO2 levels during the Late Quaternary. It was assumed that in situ chemical reactions from volcanic dust were the cause of these anomalies. However, CO2 chronologies from Greenland ice cores clearly demonstrate a sharp, short-duration decline during the Younger Dryas. Antarctic ice cores of comparable age cannot resolve such short duration shifts in atmospheric CO2.
And here’s the cherry on top of the ice cream sundae…
Stomata chronologies clearly demonstrate an abrupt spike in in atmospheric CO2 during the Bølling-Allerød interstadial (GI-1), followed by a sharp decline during the Younger Dryas stadial (GS-1). The secular rise from the last glacial maximum (LGM) to the Holocene (H) coupled with the smoothing effect of the gas age distribution in the Antarctic ice core creates a false impression of rising CO2 during the Younger Dryas.
Clearly there’s no evidence of an anomalous rise in atmospheric CO2 during the Younger Dryas. Equally troubling for the extraordinary biomass-burning episode is the collapse of atmospheric CH4 during the Younger Dryas.
The current rate of biomass-burning contributes 5-15% of the methane budget.
Resent estimates indicate that biomass burning contributes between about 20 to about 60 Teragrams per year of carbon in the form of methane to the atmosphere. This represents only 5 to 15% of the global annual emissions of methane.
The rapid burning of 9% of Earth’s terrestrial biomass should have left a mark in the methane record.
Oddly enough, biomass burning did leave a mark in the methane record. Unfortunately, it’s the wrong kind of mark for the YDIH.
Biome and Fire Regime Changes Caused by Megafauna Extinction.
Arguably, the most surprising feature of our records (Fig. 1) is the pronounced difference in absolute levels for both δ13CH4 and δD(CH4) for the Holocene compared with MIS 5.5 and MIS 11.3 and for the LGM compared with MIS 6 and MIS 12. Shifts of ∼2–3‰ for δ13CH4and 10–18‰ for δD(CH4) toward higher numbers are found, with no obvious difference in CH4 mixing ratio between these time slices (Table S1) (42). Straightforward explanations for similar [CH4] accompanied by shifted isotope records require changes in the source signatures or changes in emission strength of a source with strong leverage. To our knowledge, no general isotope shifts of that size have been described in precursor materials for methanogenesis before MIS 2. It is also unlikely that the source strength or signature of GEM (Geologic Emissions of Methane) or biogenic emissions changed markedly compared with previous glacial/interglacial cycles. In fact, GEM is expected to change in response to sea level or ice sheet extent, but the two parameters remain within a similar range for all glacials and all interstadials considered in this study. One possibility to reconcile the observations is CH4emission changes related to changes in biomes and fire regimes, because BB is a CH4source strongly enriched in 13C and D (13, 22, 65). BB (Biomass-Burning) is an ancient and persistent feature throughout the geologic record (113), and there is evidence of net changes in fire regimes as a consequence of the megafauna extinction that was presumably caused by rapid climate changes in combination with human interference in the course of the last glacial (refs. 114⇓⇓⇓⇓–119 and references therein). The review by Johnson (120) on the timing of the arrival of humans on different continents and the ecological consequences of megafauna extinction supports the idea that increased fire frequency was caused by increased vegetation density and the accumulation of plant material not consumed by herbivores. For example, records from Australia of charcoal, different plant pollen types, and spores of the fungus Sporormiella are used by Rule et al. (121) to indicate large herbivore activity and conclude that megafauna extinction caused increased fire activity after 41 ka BP. Furthermore, these Australian records show that fires were common during the Holocene but much less frequent in the previous interglacial. We note that responses might be different in other parts of the globe (122⇓–124) and that, today, Australia accounts for only roughly 6% of global fire carbon emissions (125). However, other authors reported similar observations of fire activity changes on other continents (126, 127), but a global synthesis is not available yet.
The period from the Last Glacial Maximum (LGM) through the Holocene (~25,000 yrs) exhibits elevated biomass-burning (BB) markers. Unfortunately for the YDIH, “BB is a CH4 source strongly enriched in 13C,” not a CH4 sink depleted in 13C (Melton et al., 2012).
The abrupt warming across the Younger Dryas termination (∼11,600 yr before present) was marked by a large increase in the global atmospheric methane mixing ratio. The debate over sources responsible for the rise in methane centers on the roles of global wetlands, marine gas hydrates, and thermokarst lakes. We present a new, higher-precision methane stable carbon isotope ratio (δ13CH4) dataset from ice sampled at Pakitsoq, Greenland that shows distinct ˚13C enrichment associated with this rise.
Conclusions
- There was no anomalous rise in atmospheric CO2 associated with the Younger Dryas glacial stadial. CO2 concentrations sharply declined in the northern hemisphere.
- The key biomass-burning marker, elevated 13C enriched atmospheric CH4, is totally lacking. The Younger Dryas exhibits a global decline in CH4.
Apologies
If anyone is troubled by the general lack of sarcastic smart@$$ comments in this post, I apologize. By the time I finished it up, I realized that I hadn’t liberally applied my usual dose of sarcasm and pop culture references. This is probably due to having seen Avengers: Infinity War this past weekend (two thumbs up) and I am still emotionally drained (/SARC).
References
Alley, R.B. 2000. “The Younger Dryas cold interval as viewed from central Greenland.”
Quaternary Science Reviews 19:213-226.
Anklin, M., J. Schwander, B. Stauffer, J. Tschumi, A. Fuchs, J. M. Barnola, and D. Raynaud (1997), “CO2record between 40 and 8 kyr B.P. from the Greenland Ice Core Project ice core,” J. Geophys. Res., 102(C12), 26539–26545, doi: 10.1029/97JC00182.
Bauska, Thomas K., Daniel Baggenstos, Edward J. Brook, Alan C. Mix, Shaun A. Marcott, Vasilii V. Petrenko, Hinrich Schaefer, Jeffrey P. Severinghaus, James E. Lee. “Carbon dioxide isotopes during the deglaciation.” Proceedings of the National Academy of Sciences Mar 2016, 113 (13) 3465-3470; DOI: 10.1073/pnas.1513868113
Blunier, T., J. Schwander, B. Stauffer, T. Stocker, A. Dällenbach, A. Indermühle, J. Tschumi, J. Chappellaz, D. Raynaud, J.‐M. Barnola. “Timing of the Antarctic cold reversal and the atmospheric CO2 increase with respect to the Younger Dryas Event.” GEOPHYSICAL RESEARCH LETTERS, VOL. 24, NO. 21, PAGES 2683-268. 1 November 1997 https://doi.org/10.1029/97GL02658
Bock, Michael, Jochen Schmitt, Jonas Beck, Barbara Seth, Jérôme Chappellaz, Hubertus Fischer. “Ice core isotope data constrain methane emissions.” Proceedings of the National Academy of Sciences Jul 2017, 114 (29) E5778-E5786; DOI: 10.1073/pnas.1613883114
Faith, J. Tyler, Todd A. Surovell. “Synchronous extinction of North America’s Pleistocene mammals.” Proceedings of the National Academy of Sciences Dec 2009, 106 (49) 20641-20645; DOI: 10.1073/pnas.0908153106
Hoesel, Annelies & Hoek, W.Z. & Pennock, G.M. & Drury, M.R.. (2014). “The Younger Dryas impact hypothesis: A critical review.” Quaternary Science Reviews. 83. 95–114. 10.1016/j.quascirev.2013.10.033. (Abstract only).
Holliday, V., Surovell, T, Johnson, E (2016) “A Blind Test of the Younger Dryas Impact Hypothesis.” PLoS ONE 11(7): e0155470. https://doi.org/10.1371/journal.pone.0155470
Koch, Paul L. and Anthony D. Barnosky. “Late Quaternary Extinctions: State of the Debate.” Annu. Rev. Ecol. Evol. Syst. 2006. 37:215–50
Levine, J. S. (1990), “Global biomass burning: Atmospheric, climatic and biospheric implications,” Eos Trans. AGU, 71(37), 1075–1077, doi: 10.1029/90EO00289. (Abstract only).
Levine, J., W. Cofer, III, AND J. Pinto. (2002) “BIOMASS BURNING AND THE PRODUCTION OF METHANE.” U.S. Environmental Protection Agency, Washington, D.C., EPA/600/A-92/221 (NTIS PB93119824). (Abstract only).
Marcott, Shaun A., Thomas K. Bauska, Christo Buizert, Eric J. Steig, Julia L. Rosen, Kurt M. Cuffey, T. J. Fudge, et al. “Centennial-Scale Changes in the Global Carbon Cycle during the Last Deglaciation.” Nature 514, no. 7524 (2014): 616–19. doi:10.1038/NATURE13799.
Melton, R., J & Schaefer, Hinrich & J. Whiticar, M. (2011). “Enrichment in 13C of atmospheric CH4 during the Younger Dryas termination.” Climate of The Past Discussions. 7. 10.5194/cpd-7-3287-2011.
Moore, Christopher & Brooks, Mark & Mallinson, David & Parham, Peter & Ivester, Andrew & K. Feathers, James. (2016). “The Quaternary evolution of Herndon Bay, a Carolina Bay on the Coastal Plain of North Carolina (USA): implications for paleoclimate and oriented lake genesis.” Southeastern Geology. 51. 145-171.
Moore, Christopher & West, Allen & Lecompte, Malcolm & Brooks, Mark & Randolph, I & Goodyear, Albert & Ferguson, Terry & Ivester, Andrew & K Feathers, James & P Kennett, James & Tankersley, Kenneth & Adedeji, A.V & E Bunch, Ted. (2017). “Widespread platinum anomaly documented at the Younger Dryas onset in North American sedimentary sequences.” Nature: Scientific Reports. 7:44031. 1-9. 10.1038/srep44031.
Prideaux, Gavin J., Grant A. Gully, Aidan M. C. Couzens, Linda K. Ayliffe, Nathan R. Jankowski, Zenobia Jacobs, Richard G. Roberts, John C. Hellstrom, Michael K. Gagan, Lindsay M. Hatcher. “Timing and dynamics of Late Pleistocene mammal extinctions in southwestern Australia.” Proceedings of the National Academy of Sciences Dec 2010, 107 (51) 22157-22162; DOI: 10.1073/pnas.1011073107
Wolbach, Wendy & Ballard, Joanne & A. Mayewski, Paul & Adedeji, Victor & E. Bunch, Ted & B. Firestone, Richard & A. French, Timothy & Howard, George & Israde-Alcántara, Isabel & Johnson, John & Kimbel, David & Kinzie, Charles & Kurbatov, Andrei & Kletetschka, Gunther & Lecompte, Malcolm & Mahaney, William & L. Melott, Adrian & Maiorana-Boutilier, Abigail & Mitra, Siddhartha & P. Kennett, James. (2018). “Extraordinary Biomass-Burning Episode and Impact Winter Triggered by the Younger Dryas Cosmic Impact ∼12,800 Years Ago. 1. Ice Cores and Glaciers.” The Journal of Geology. 126. 000-000. 10.1086/695703.
Double Apologies
This morning, after reading one of the Joanne Ballard’s comment, I realized I left their paper, the subject of this post, out of the references… An omission I just rectified.
Thanks David.
If you like this one, you’ll love Part Quatre! No Younger Dryas, all geology…
Here’s a left field hypothesis from Firestone.
The N American ice sheet at the end of the last ice age breaks up because of a meteorite impact that smashes it.
But the meteorite is radioactive and affects all the geology at the time.
Because of this that sedimentary layer is mis-measured for it’s age.
And so the end of the last ice age is seen to be a lot later than it is – a second mini, phantom ice age that never existed.
That mistimed cold period is given the name the “Younger Dryas”. But it’s actually the end of the previous cold period pushed up the timeline by measurement error.
I have no clue what people see as so great about the Avengers movie. Saw it three days ago and still trying to fully digest the yummy popcorn and licorice. I don’t think it was bad but just seemed like another run of the mill comic book movie to me.
Have you seen all of the preceding Marvel Cinematic Universe movies?
I like the doctor one best but doubt I’ve seen them all
Strange.
The villain is a PC Malthusian who wants to kill half the people in the universe (regardless of wealth, creed or colour) just so as the rest don’t run out of resources.
That’s slightly less evil than most Greens who want to kill half of all people chosen on wealth – only those poorer than themselves.
It’s interesting that terrible comic book villains are less horrific than the Club of Rome.
And that such a portrayal is very populist.
Malthusian: Yes. Thanos is like a 9′ tall Paul Ehrlich.
PC: Thanos?
Politically Correct. In the movie Thanos is very PC.
Race. Creed. Colour.
Species. Home. Ideology.
Wealth. Power. Family.
All are disregarded. All are equal.
He will kill half of all regardless of privilege.
I try to not think too deeply when I’m watching a raccoon fly a space ship
Rabbit.
Hint: Thanos is the bad guy!
Well I appreciate your efforts David as I have always been fascinated by the whole punctuated evolution/ impact account of our understanding of Earth history as it has developed over the recent decades. I agree that we cannot be definitive yet but If we find the presence of elements rare on Earth but common in asteroids/comets/meteorites scattered about then we have to take the matter seriously. And I see no reason to doubt that Earth has been hit by large lumps from space much more often than is obviously preserved by a constantly reweathered surface.
On the humour/sarc front, I now realise the ten per cent raise in CO2 claimed was caused by evil early humans powering up their SUVs to race around killing any megafauna that moved, thus explaining how their small numbers could inflict so much eco-destruction in short order. It was all our fault.
My biggest pet peeve about the YDIH is the “fake evidence.” I think the enthusiasm to promote this hypothesis gets the better of its proponents. I sometimes wonder if there is actually a quasi-political angle. If an impact took out the megafauna, then humans and our dogs would be off the hook. 😉
As an actual lifelong hunter, I find it hard to conceptualize people 12, 800 years ago being capable of wiping out megafauna with or without dogs. No way Jose’. Didn’t happen. Big critters are hard to kill, let alone wipe out by hunting. Destruction of habitat is another story but don’t think people 12, 800 years ago were doing or capable of doing much of that either. Not enough of them nor technologically advanced enough either.
Pure opinion, on my part, but we still have elk and deer and buffalo in spite of our modern day attempts, intentional or not, to wipe them out. And wolves and mountain lions as well.
Since you live in North America you have never hunted Megafauna. There isn’t any. No mammoths, no mastodons, no giant sloths, no horses, no camels, no tapirs, no lions, no sabre-tooths, no short-faced bears, no saiga, no…
Very large animals may be hard to kill, but stone age hunters managed to do it, even hundreds of thousand years ago, probably by hunting in groups. Google “Cotte de Saint Brelade” or “Lehringen spear”.
And very large animals breed very slowly. Even if a hunting tribe only managed to kill a mammoth every few years it would probably still be enough to exterminate a local population.
+100
tty May 15, 2018 at 6:34 am
We do have some surviving megafauna, but not the largest. Lots of North American animals weigh more than 44 kg.
Bison routinely weigh over a ton. The largest confirmed Alaskan moose, shot in 1897, weighed 820 kg, but reports of even bigger ones have been credibly made. Roosevelt elk of the Cascade Range reach 600 kg.
Musk oxen weigh 250 kg on average. A white tail deer killed in 1926 weighted an estimated 232 kg, but the biggest today weigh around 125 kg. Mule deer bucks’ normal range tops out at 150 kg. Big horn sheep can reach 140 kg or more.
We also have some enormous pigs (both native wild and feral domestic), bears and cougar (pumas). The Kodiak grizzly weighs up to 680 kg, and polar bears 700 kg or more.
But I agree that Paleolithic hunters did kill even the largest megafauna, ie mammoths. The evidence is conclusive.
There is also the fact that megafauna have repeatedly gone extinct after the arrival of humans, as in Australia, New Zealand and other islands. Same happened in the Americas.
The YD didn’t kill off the megafauna of North America. People did. If an impact were responsible, why did megafauna survive on Caribbean islands, while dying out in Florida and Mexico, only finally to succumb thousands of years later, after people made it to the islands?
Pronghorn, mountain “goats” and caribou also weigh more than 44 kg.
There is still a lot of big game in North America, even though we now lack wild members of the elephant family, plus no rhinos or giraffes. Not that I would ever shoot a giraffe, although they are dangerous.
We also have too many feral horses, but aren’t allowed legally to hunt them.
DO they not wonder how the CO2 can spike a huge high and the temperature plummets?
Do they really think that there were enough Clovis people to alter the climate? Really? It is patently unlikely that they slaughtered whole herds of animals to get a good meal. It insults those people.
If you think about how drastically the climate would have been changing in North America during stadial-interstadial transitions, and even more so during glacial-interglacial transitions, and how that would have affected habitat ranges, megafauna populations were probably already seriously stressed when humans arrived in the Americas.
However those were stresses which the megafauna survived during the termination before the Eemian interglacial, which was hotter than the Holocene.
I have been following Graham Hancock as he explores this impact theory. I believe this video puts a lot of evidence on the table in reference to what David is referring to. If you have 1-1/2 hours to spare, it does make a case.
This is great! I love the discussion and hearing hard questions being asked.
Love reading the info, I’m guessing that no one has given any “real” numbers on the megafauna which existed prior to the YD. I suspect those numbers might be on the order of the swags regarding the number of polar bears, with the same caveats. Not to mention any kind of swag on the number of the new kids on the block hunting same… ms-phd
Mark Twain was right.
What caused all those other up and downs?
The same thing that caused the Younger Dryas (not impacts).
The same ups and downs have also been observed in previous glacial terminations.
The YGIH fails on its face, since the null hypothesis can’t be rejected. The YD was no different from all the other cold spells, and happened for the same reason, ie a pulse of cold, fresh water into the Atlantic.
Global warming ended ten thousand years ago.
The Holocene is different to previous interglacials, the YD put a damper on temperatures and civilisation flourished.
So it begs the question, would humanity be where it is today without the YD?
The Holocene isn’t different in any way. It’s totally normal so far. It is colder than the prior Eemian and hasn’t yet lasted as long, but it’s warmer and has lasted longer than some others.
The YD is a totally ordinary termination event, requiring no special explanation.
The ordinariness of the YD doesn’t preclude the possibility that an impact *might* have played a role in the Rancholabrean extinction.
One of the problems is that this has been approached form the perspective of the impact event causing the YD and the Late Quaternary extinctions. If they would just step back from extraordinary claims, they might be able to make a decent case for a significant impact or bolide. By significant, I mean bigger than Tunguska, but infinitesimal compared to Chicxulub.
David,
Few extinctions took place during the YD, especially when focusing in on its start. Were they higher than during intervals before and after the YD?
Hence, IMO, there is no need to invoke a Pt-containing impact or airburst, although that unlikely event can’t be ruled out. Again, though, where are the other chemical markers of such an impact or explosion?
Maybe they exist. I haven’t read the paper on the alleged Pt spike.
The Pt papers are on my “to do” list. It’s a long list.
About 40% of the Rancholabrean extinctions do appear to have occurred during the YD. I haven’t taken the time to examine that in detail to see if it’s a significant excursion from the overall Late Quaternary extinctions.
I don’t know the volcanic history of Ontario, but maybe a volcano erupted in the Sudbury Basin as the mass of ice was lifted by retreat of the Laurentide Sheet. Platinum from such a hypothetical eruption could be carried by prevailing winds to Greenland.
It the Pt excursion shows up elsewhere in North America, then this conjecture would not be confirmed.
Again, no explanation needed other than the entry of humans:
South American extinctions:
http://1.bp.blogspot.com/-YHODCFi2Ja0/VPdz1iMpDJI/AAAAAAAAPiQ/DC6kkL8y7YY/s1600/SouAmeSix.jpg
David,
These guys support an event along your lines (2013):
http://www.pnas.org/content/110/32/12917.full
While these guys don’t (2009):
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2799824/
Although this study predates Petaev et al. (2013) and Moore (2017).
http://www.pnas.org/content/110/32/12917.full
https://phys.org/news/2017-03-discovery-widespread-platinum-clovis-people.html
As noted, I haven’t read the full papers, only abstract or press account.
It’s like watching a tennis match. It always comes back to 1) results that aren’t consistently reproducible 2) evidence that is either not unique to the YD, postdates or predates the YD.
Why do we need impact craters?
Would a grazing strike not result in the equivalent of an atomic airburst? with the ‘dirty snowball’ simply exploding and vaporising? Like Tunguska, but bigger….
Hence the PGE anomalies.
IMO the Pt spike isn’t unusual. The lack of other ET elemental markers suggests a terrestrial source. Pt is mined in central Ontario, Canada.
The Sudbury Basin is however an impact structure. Its crater is the third largest known, dating from 1.849 Ga.
True… Impacts usually due exhibit a broad spectrum of PGE anomalies, not just Pt.
That was part of Paquay’s shoot down of Firestone.
David, in the past I have also looked with interest at the YDIH, mainly because of the Pt spike in ice cores. There are however multiple problems with the hypothesis, not the least that some proponents of the hypothesis clearly have misrepresented the evidence, leading to acrimony. The best examples are the spherules, and the Carolina Bays, both shown to be bogus evidence. Not the best support for a hypothesis.
So, I have two problems with the hypothesis. The first one is that every claim, when examined in close detail, either dissolves, like you have done here with the CO₂ claim, or becomes difficult to interpret. Yes there is a Pt spike, but metallic meteorites are characterized by a signature of rare elements, so in addition to Platinum, there are usually also Iridium, Palladium, Ruthenium, and Rhodium. If there are no peaks of some of the others this is truly an anomalous meteorite.
And my second problem is that a lot of things were taking place at the time that could have contributed to the Younger Dryas.
For a start the YD was not so anomalous. The cooling from Bølling that produced the Older Dryas was similar (another meteorite?). It is flanked by two very abrupt warming periods in the NH, that are separated by 1500 years
So clearly the YD fits nicely within the series of Dansgaard-Oeschger events. Not only that but it also fits nicely within the Heinrich cycle characterized by a huge increase in iceberg activity in the North Atlantic.
If this wasn’t enough. The start of the YD coincides with one of the strongest volcanic eruptions in terms of volcanic sulphate in ice cores:
Baldini et al. have a paper submitted to Climate of the Past about the Laacher See volcanic eruption and the Younger Dryas:
Baldini, J. U., Brown, R. J., & Mawdsley, N. Re-evaluating the link between the Laacher See volcanic eruption and the Younger Dryas.
https://www.clim-past-discuss.net/cp-2017-147/cp-2017-147.pdf
“recently revised stratigraphic frameworks for key climate archives now suggest that the Laacher See eruption was in fact synchronous with cooling associated with the YD onset (i.e., GS-1), but preceded atmospheric circulation shifts over central Europe. Here we use GISP2 ion data (Zielinski et al., 1997) on the GICC05modelext chronology to identify a large sulphur spike whose timing is consistent with the Laacher See eruption, and argue that short-lived volcanogenic aerosol cooling triggered a positive feedback that led to dynamical changes most closely associated with the YD.”
Although in my opinion increased volcanism could not have cause the YD, it could certainly have contributed to the steep cooling detected in Greenland ice cores at the onset of YD.
And if all this wasn’t already a heap of unfortunate events, The YD cooling belongs to the 2500-year Bray cycle of solar activity coinciding with a major through in solar activity, clearly detected in the Radiocarbon series IntCal13. It corresponds to B6.
In case there is any doubt:
Renssen, H., van Geel, B., van der Plicht, J., & Magny, M. (2000). Reduced solar activity as a trigger for the start of the Younger Dryas?. Quaternary International, 68, 373-383.
https://www.rug.nl/research/portal/files/6661387/2000QuatIntRenssen.pdf
So the question is if with all the factors that coincided at the YD-onset, all of them capable of affecting temperature, Heinrich event, Dansgaard-Oeschger event, Laacher See volcanic eruption, and LIA-like solar minimum, do we also need the cosmic coincidence of a meteorite to produce the YD?
The answer is clearly not. We do not need extraterrestrial causes to explain the YD, and quite frankly, the evidence for the impact is rather poor.
The most likely explanation is that a coincidence of several causes, each of them capable of contributing to the YD, at the same time, in a particularly sensitive period, while the glacial termination was proceeding driven by feedbacks, sabotaged the start of our interglacial. Due to the long previous glacial period, our interglacial was destined to be as warm as the Eemian, and have a similar shape with a warmer earlier period. Instead our interglacial has a funny shape, being warmer at the middle.
Regarding the impact-driven extinction. This is just folklore added to the impact hypothesis by scientists that know nearly nothing about such things. The cultural shift at the termination of the Clovis culture does not require an impact. There is so much knowledge about cultural shifts associated to climate change that I wouldn’t know where to start. Interested people can read my article:
Impact of the ~ 2400 yr solar cycle on climate and human societies
https://judithcurry.com/2016/09/20/impact-of-the-2400-yr-solar-cycle-on-climate-and-human-societies/
Javier,
I don’t disagree with you at all. You really nail it here:
The stadial-interstadial-stadial transitions of the Late Pleistocene would have already been extremely stressful to slow-reproducing magafauna. Toss in humans, domesticated wolves and maybe, possibly a significant bolide…. And it’s lights out.
Yes, indeed.
And, as David’s graph shows, what is most unusual is the warmth of the prior B-A warm spike (a D-O event), not the depth of YD cold, which wasn’t any worse than the Older and Middle Dryases, nor comparable variations during previous terminations. So the YD just looks worse in comparison with the preceding warmth.
Smack in between the warmest interstadial and the Holocene.
I find it silly in the first place to try to explain extinctions. Extinction is the normal. Survival is the thing you need to explain.
so, why megafauna appeared and survived? What are the conditions for megafauna to prosper? why, for a given amount of available food, a specie would have an edge growing a single big, long lived, individual rather than 2×2 smaller, shorter lived?
It take rather special conditions for this.
1) very stable but complicated ecological conditions, where long learning and fine tuning prevail and favor to K strategy over r strategy, and evolution to adapt to changes doesn’t matter so much.
2) cold climate. Animals produce heat as cube of size and lose it as square, so doubling size is doubling production/loss ratio. Notice that birds have much more efficient coating than mammals. Because they need it. mammals have pretty inefficient hair, but efficient enough. But big animals don’t prevail, except rather far north (moose).
3) for predators: ability to roam an area big enough to find prey of the relevant size, not too small, not too big. Current big cats seems the maximum size. Being bigger currently brings no edge. Maybe it would if vegetal productivity were higher, allowing more herbivore mass (whether big or small); not sure.
4) for prey: predation high level enough, and of such a kind that size matters more than speed or other way to fend off predators. Obviously not true nowadays, so why would it be true a few millennia ago?
Explaining the “when” is the fun bit.
Megafauna is the normal state. Most animal lineages tend to grow larger over time. Yes, megafaunal species die out and are replaced by others. What is exceptional for the Late Pleistocene is that almost all megafaunal species in North America, South America, Australia, and Northern Eurasia go extinct within a geologically very brief interval, and without replacement.
This is very unusual.
Particularly since the extinctions seemed to closely follow the arrival of people.
A MAMMOTH CENSUS? wsbriggs, “real” numbers in populations of megafauna, there were no known censuses taken of those animals by any paleopersonnel. Therefore we must rely on the fossil record, and only a small percent of animals fossilize. La Brea Tar pits is an exception. I might point out that hundreds of thousands of tusks have been mined from the Ivory Islands north of Siberia, and while these must span many thousands of years, populations of mammoths and other megafauna were likely teeming across Eurasia and North America.
MISSING IMPACT CRATER: if the impactor or swarm of comets struck a two mile thick ice sheet (the Laurentide), much of the energy would be taken up converting ice to water and any crater in the Laurentide carcass would eventually melt away.
PLATINUM: The Petaev et al. (2013) paper on a platinum spike in the Greenland ice cores at 12,800 is important, followed by Christopher Moore’s work (Moore et al. 2017) on a terrestrial YDB signal in sediments.
BLACK MATS AS YDB EVIDENCE: Consider the black mats that are prevalent in the Southwest and other parts of North America (Haynes 2008) and in Europe (the so called Usselo horizon). These are charcoal rich, algal rich layers that mark the onset of the Younger Dryas. I have studied samples from 4 locations in the Netherlands and Belgium, and those burn layers in the coversands are characterized by charcoal, algae, sponge spicules, very small smoothed black grains, fused quartz and melt glass. Wildfires typically don’t burn hot enough to melt quartz. See my report “Quartz melt structures in European coversands may support Younger Dryas extraterrestrial impact hypothesis”
https://www.researchgate.net/profile/Joanne_Ballard/contributions
MASSIVE VEGETATION SHIFT AT YDB. We know from many pollen records that a major shift in vegetation occurred roughly around the beginning of the Younger Dryas. It can be tough to get a precise date on lake sediments, as there may be hiatuses or lack of terrestrial material to radiocarbon date.
NITROGEN EVIDENCE: Also, one of the characteristics of an extraterrestrial impact is the associated shock wave. Nitrogen in the atmosphere is dissociated, the ozone layer is damaged and nitrates form. These rain out as nitric acid rain for months to a year or so. Nitric acid rain is damaging to leaves and aquatic animals but algae love it – we know this from historic studies of acid rain effects in the Smokies and Scandinavia. It is a nutrient input for algae – look for massive algal blooms at the YDB- they are there. Following the nitrogen signal (total nitrogen peaks and disturbances in 15N) may provide some insight at YDB. Kolesnikov (1998) showed changes in nitrogen isotopes for 1908, the Tunguska impact in Siberia. I predict we will find this at YDB if high resolution analysis of lake sediments is conducted. Diatoms are useful to determine changes in acidity in the past. This could be used as a test of the YDIH. Sergey Leshchinskiy reports widespread skeletal problems for mammoth in Siberia, which he attributes to acidification of the landscape leading to mineral deficiencies. This worsened during the late glacial. The late glacial environment became very inhospitable, not only in Siberia but in North America and Europe. This brought about environmental-triggered diseases.
HOLLIDAY FOLLY: Holliday and his group failed to use sieves to separate sediment into size fractions.
REFERENCES
Haynes Jr., C.V. 2008. Younger Dryas “black mats” and the Rancholabrean termination in North America. Proceedings of the National Academy of the Sciences 105 (18): 6520–6525.
Kolesnikov, E.M.; Kolesnikova, N.V.; Boettger, T. 1998. Isotopic anomaly in peat nitrogen is a probable trace of acid rain caused by 1908 Tunguska bolide. Planetary Space Science 46 (2/3):163–167.
Leshchinskiy, S.V., 2009. Mineral deficiency, enzootic diseases and extinction of mammoth of Northern Eurasia. In Doklady Biological Sciences 424 (1): 72–74.
Moore et al. 2017. Widespread platinum anomaly documented at the Younger Dryas onset in North American sedimentary sequences https://www.nature.com/articles/srep44031
Petaev, M. I., Huang, S., Jacobsen, S. B., & Zindler, A. 2013. Large Pt anomaly in the Greenland ice core points to a cataclysm at the onset of Younger Dryas. Proceedings of the National Academy of Sciences, 110(32), 12917–12920.
The Usselo horizon is no “black mat”. It is a perfectly normal soil horizon formed during the Alleröd interstadial and early YD.
That is what some contend, but I disagree. It is not a “perfectly normal” soil horizon. It contains soot, charcoal, melt glass, fused quartz, and wood that is glazed in silica.
Dr. Ballard,
I agree that the Pt anomalies are interesting and could be evidence of a significant bolide or impact… What bugs me are what seem to be ancillary arguments that are often poorly supported or totally unsupported.
How could 9% of Earth’s terrestrial biomass go up in smoke without a spike in atmospheric methane? Before asserting a YD rise in CO2, did you look at any other CO2 data besides Brooks? Particularly northern hemisphere data which demonstrate a drop in CO2. Has there been any consideration of the fact that Antarctic ice cores exhibit continued warming throughout the YD?
I think there’s a fair bit of evidence for some sort of bolide. The particularly rapid extinction of about 40% of North American megafauna and the demise of the Clovis culture clearly occurred around YD time. Some sort of regional catastrophe seems plausible. However, it seems that this is insufficient unless the YD impact can be put on a comparable level as the KT impact.
Hi David. Well, keep in mind that methane cycles through the atmosphere in about 10 yrs. The Greenland Ice has firn (old snow) above the ice which may take up to 100 years to seal up. During that time, the atmosphere can move through it, and the signal could be averaged. The firn depth at Summit greenland is 85 m. http://cdiac.ess-dive.lbl.gov/trends/atm_meth/lawdome_meth.html
Also, it seems to me that if we had thermal pulse associated with an extraterrestrial impact, there should be some melting of the surface of the Greenland Ice Sheet (adjacent to the Laurentide ice sheet at 13,000 yrs BP). I have not personally worked on ice cores though to know what a hiatus would look like there. I work on sediment cores, focusing on charcoal, pollen, and geochemistry.
I don’t think there’s much, if any, evidence of melt layers from cores near the summit. The GRIP core is near the summit and it clearly shows a drop in CO2 during the YD. Melt layers are relatively common in lower altitude cores like DYE-3 (about 1 per century). DYE-3 also shows a YD drop in CO2.
The Greenland ice cores tend to have very high resolutions due to the snow accumulation rates. The atmospheric mixing time is much less than Antarctic cores, with the exception of the Law Dome DE08 core, but it only goes back about 2 ka.
Also… Thank you for taking the time to join the discussion here.
Haynes, 2010 did not find what Firestone, et al, claimed to have found:
http://www.pnas.org/content/107/9/4010
The Murray Springs Clovis site, Pleistocene extinction, and the question of extraterrestrial impact
Nor did he find iridium:
http://www.pnas.org/content/106/51/21505.short
Absence of geochemical evidence for an impact event at the Bølling–Allerød/Younger Dryas transition
Nor did Haynes find that megafaunal extinctions occurred at the onset of the YD, but rather hundreds of years later:
https://www.tandfonline.com/doi/abs/10.1080/20555563.2016.1174559
On the Dating of the Folsom Complex and its Correlation with the Younger Dryas, the End of Clovis, and Megafaunal Extinction
We know that some mammoths lived beyond 12,800 years into the Holocene, and they are all found on islands: Wrangel Island (Siberia) date to some 4000 years ago; the Channel Islands off the California coast, Pribilof Island (near Alaska). So obviously, stragglers managed to survive, but the populations as a whole sustained massive stress. Some species survived in North America–e.g. deer, elk, bears. There were major shifts in ranges of animals.
Haynes should go back and look for Platinum.
The problem for impact advocates is that there is no signal in the megafaunal extinctions associated with the onset of the YD.
Some megafauna went extinct before it, some during it and some after it, while others survived. None went extinct right at the YD onset. Megafauna which should have gone extinct with those which did during the YD, didn’t, such as giant ground sloths of the Caribbean. Why didn’t the alleged impact kill them, if it supposedly killed those in FL, in the US NE, SE, SW, Mexico and northern South America, plus those much farther afield, such as in Alaska and the NW USA?
Yet the sloths and other megafauna died out whenever and wherever people arrived to hunt them, which was delayed thousands of years in the Caribbean.
Pt is not a signal of ET impact, unless associated with other chemical markers, such as iridium.
Sorry, but there is simply no valid evidence of an impact at the YD.
David,
A nieve observer would look at figure 1 in your post and say that it looks like the signal that would be produced by a sputtering motor. At regular intervals, you have the Dansgaard-Oeschger (D-O) warm events firing up throughout the depths of the last Ice-Age. This is like someone repeatedly turning the ignition key on their car only to have the engine die every time. Using this analogy, you might suspect that something is trying to shift the Earth’s climate system from its glacial to its interglacial phases but there is not enough umph to get the transition to take place.
However, this all changes at the Bolling Allerod interstadial. A DO-event takes place upon a rising background temperature. This gives it that extra umph to temporarily kick the Earth’s climate from its glacial to its inter-glacial mode. Unfortunately, the engine sputters and the Earth’s climate system falls back into its glacial mode. It’s not until the next DO event at the end of the Younger-Dryas (Y-D) that key is turned and the engine finally fires up and begins running on all cylinders, entering the current interglacial period.
This intuitive picture leads me to suspect that it is the DO events that are responsible for the temperaure that occurred during the transition from the glacial to the intergalcial (including the YD event) and that the DO events are in fact a response to lunar tidal forces.
If anyone is interested, I argue my case over at http://astroclimateconnection.blogspot.com.au
Are the Dansgaard-Oeschger (D-O) Warm Events driven by Lunar Tides?
Sunday, June 23, 2013
DO Events Cause Rapid Warming Events in the Last Glacial Period
Tuesday, January 14, 2014
David,
A nieve observer would look at figure 1 in your post and say that it looks like the signal that would be produced by a sputtering motor. At regular intervals, you have the Dansgaard-Oeschger (D-O) warm events firing up throughout the depths of the last Ice-Age. This is like someone repeatedly turning the ignition key on their car only to have the engine die every time. Using this analogy, you might suspect that something is trying to shift the Earth’s climate system from its glacial to its interglacial phases but there is not enough oomph to get the transition to take place.
However, this all changes at the Bolling Allerod interstadial. A DO-event takes place upon a rising background temperature. This gives it that extra oomph to temporarily kick the Earth’s climate from its glacial to its inter-glacial mode. Unfortunately, the engine sputters and the Earth’s climate system falls back into its glacial mode. It’s not until the next DO event at the end of the Younger-Dryas (Y-D) that key is turned and the engine finally fires up and begins running on all cylinders, entering the current interglacial period.
This intuitive picture leads me to suspect that it is the DO events that are responsible for the temperature that occurred during the transition from the glacial to the interglacial (including the YD event) and that the DO events are in fact a response to lunar tidal forces.
If anyone is interested, I argue my case over at http://astroclimateconnection.blogspot.com.au
Are the Dansgaard-Oeschger (D-O) Warm Events driven by Lunar Tides?
Sunday, June 23, 2013
DO Events Cause Rapid Warming Events in the Last Glacial Period
Tuesday, January 14, 2014
In Renee Hannon’s post
https://wattsupwiththat.com/2017/08/04/paleoclimate-cycles-are-key-analogs-for-present-day-holocene-warm-period/
She highlights previous interstadials that have a Younger Dryas feature and an 8.2 K feature.
What goes around comes around, heh.
Sandy, Minister of Future
Earth works that way.
Great post, as usual, David. I love this topic and, for me, this is the most fun part of science. Holding various pieces of the puzzle up to the light for examination and then trying to fit them into some kind of coherent whole that makes some kind of sense!
I’ve debated on whether or not to dangle the following tidbit out there (it IS kind of a jacka** thing to do), BUT I’m doing it anyway. I happen to know that there’s a paper in the final stages of peer review and publication that is going to be the biggest news on this topic in quite some time. Maybe ever. However, I am not authorized to say any more about it than that. So, stay tuned, kids….
JW
Geology & geophysics…
https://en.wikipedia.org/wiki/Blind_men_and_an_elephant
That’s perfect. The wise man knows that he is also blind. I told some colleagues recently that science is much more enjoyable when you reconcile with the idea that everything we ‘know’ about the past is probably wrong.
I think the blind men and the elephant parable was included in the preface to an atlas of seismic stratigraphy back in the 1980’s.
Be sure to let me know when the paper is out of embargo!
I certainly will! We hope to have the authors on the podcast, as well.
Cool!
I want to know as well.
If nothing else, the YDIH is a great example of scientific debate… 👍👍
David this is a magnificent piece. A veritable Sherlock Holmes-type geological analysis that you rarely see since the preCliSci geological Mass Thought Extinctions. I can see that the new ge-o-golliest’s minds are handicapped by the CO2 societal control knob and the grant gravy. Dont they know this is drying up. Even Ozzies who love this death by climate science stuff are slashing budgets for more of it.
Thanks! Although, in fairness to the authors, I don’t think they were “handicapped by the CO2 societal control knob and the grant gravy.”
I think it’s more a matter of too many variables to keep track of.
Another great presentation, David. I love this series and all the comments, too.
Here’s another explanation.
The YD was actually a period of rapid warming. Lake Agassis lost containment flooding much of North America and blanketing the North Atlantic with meltwater.
Cold temps indicated by the Greenland Ice Cores. Meltwater is depleted in O18 which evaporated and deposited on Greenland giving a false indication of cold temperatures.
Extinctions. Large areas of North America were flooded when Lake Agassiz lost containment, producing massive habitat loss and extinctions for many animals.
CO2 spike missing. Flooding killed off much plant life as well, so photosynthesis greatly reduced.
Just realized that reduced photosynthesis would increase atmospheric CO2, so never mind.
There are some alternative theories. Dr. Michael Mann (yes *THAT* Dr. Michael Mann) claims that rapid release of meltwater from glaciers at the end of the latest ice age flooded the North Atlantic with fresh water and shut down the AMOC (Atlantic Meridional Oveturning Circulation). The Younger-Dryas cold event is claimed to be a real-life version of “The Day After Tomorrow”.
One question he doesn’t address. 20,000 years there were maybe 1 million Homo Sapiens on planet earth and CO2 levels were half their current level. So how come the 2-mile-thick glaciers started melting suddenly, with occasional major releases of meltwater as it built up and ice dams occasionally collapsed?
Another alternative theory is a “super-Carrington event”. The paper at https://journals.uair.arizona.edu/index.php/radiocarbon/article/viewFile/3464/pdf calls it an “SPE” (Solar Proton Event). This is a serious paper, with 21 pages of mostly text, and some graphs/charts/tables.
100% science fiction…
http://ufology.wikia.com/wiki/Paul_LaViolette
Did you see this paper?
https://www.academia.edu/2949675/Stomatal_proxy_record_of_CO2_concentrations_from_the_last_termination_suggests_an_important_role_for_CO2_at_climate_change_transitions
I had not seen this one… Thank you!
>400 ppm during the Allerød… Awesome!
Glad to know that 400 ppm is nothing unusual even while still in glacial phases.
But their conclusion that CO2 plays a role in terminations is simply idiotic. If CO2 were so powerful, how did the YD even happen, given 400 ppm during the preceding warm interval?
Clearly, as is already known, CO2 increase is caused by warmer conditions. It doesn’t cause them. The YD cold snap occurred, according to this study, under CO2 levels similar to now.
The authors aren’t stupid. They knew that the CO2 warming angle was the way to get their research funded and published. But their conclusion is absurd on its face.
It does play a role… it goes up when the oceans warm… 😎
David, I installed granite countertops from Vittoria, Brazil. It has an artifact with perfectly square corners and a perfectly straight edge about 10-3/4 inches between the corners. The color is white while the surrounding granite is a dark gray. Have you seen artifacts like this? Any explanation?
Jeffery Larson, we need photos. Could be an anthropogenic patch.
My first attempt at posting a picture
Attempt #2
Probably not… but I’d love to see a picture! Most “granite” countertops aren’t actually granite. They are quite often gneiss and other wildly deformed metamorphic rocks. Our house and outdoor living area are loaded with cool “granite” countertops… only one is actually granite.