Extraterrestrial impact kills megafauna?

[Andre]

I'm still working on the last glacial transition. The other week I drafted this comment:

Some remarks on
"Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling"

by R. B. Firestone et al. 2007


Introduction

Firestone et al. 2007 link evidence of an unidentified extraterrestrial event (ETE) to the onset of the Younger Dryas cooling which may have contributed to the megafauna extinction. We do not contest the evidence or occurrence of this extraterrestrial event, but the proposed consequences meet a considerable challenge when confronted with other evidence. We intend to demonstrate that the timing for the onset of the Younger Dryas is at odds with the bulk of the evidence. Furthermore, comparison of isotope records of multiple proxies show the same characteristics for the termination of the Dansgaard Oeschger events as well as the Bølling-Allerød events, suggesting that no foreign cause is required to explain the termination of the latter. Finally, on a global scale, the extinction of the megafauna happened rather gradually between 18,000 and 4,000 years ago in North America, but many endemic species did not die out from the event.

The dating gap of the onset of the Younger Dryas exceeds the error margin

Based on two series of carbon dates which mark the end of the Clovis stratum, Firestone et al. establish the dating of the ETE at 12.9 +/- 0.1 ka Cal BP. This date is cross-checked with the onset of the Younger Dryas in the Greenland GISP-2 ice core marked by a sharp drop of water isotopes.

These carbon date series, averaging 10,890 14C years and 10,940 14C years BP, would calibrate to 12.87 and 12.88 ka Cal BP using the INTCAL04 calibration table (Reimer et al., 2004) while the article mentions 12.92 and 12.93 ka Cal BP, which is likely based on the previous INTCAL98 calibration table (Stuiver et al., 1998).

We compare the isotope records of the major Greenland ice cores for the period of the onset of the Younger Dryas marked by a sudden drop in d18O isotope values of about 4-5 mil.

Insert fig1 here

Caption:
d18O records of the main Greenland ice cores during the onset of the Younger Dryas. Vertical lines show approximately the neutral average isotope value to denote the onset of the Younger Dryas. Datasets are obtained from NOAA (Grootes, P.M., and M. Stuiver. 1997, Johnson et al., 1997, NGRIP members 2004) Note that the “present” base for NGRIP is 2000AD, this was converted back to the standard “present” of 1950AD. Also double isotope values per date have been averaged for smoothing.

NGRIP and GRIP both suggest that the Bølling Allerød to Younger Dryas transition is between 12,700 and 12,650 calendar years BP. This conflicts with the GISPII chronology which suggests around 12,850 years ago for the beginning of the Younger Dryas. Although the difference is small, there is still the larger part of the last Allerød spike in between. Hence, the date of 12,900 years ago of Firestone et al., 2007 is off by a sufficient margin to miss that spike. Therefore, it would be advisable to crosscheck this boundary with other, independent, high resolution chronologies.

The most accurate dating may be found by counting lake varves and correlating these to several well-dated tephra layers (Zolitschka et al., 2000). The records of the Meerfelder maar (Lücke and Brauer, 2004), Lake Gosciaz, (Goslar et al., 1995), the Ammersee (von Grafenstein et al., 1995) closely follow the GRIP ice core chronology. Hence, high resolution records independently reproduce an onset of the isotope Younger Dryas at around 12,675 +/- 25 varve years BP, (see http://www.gfz-potsdam.de/pb3/pg33/projects/eifelmaar/index.html ) which is more than two sigma outside the error range of the date of the ETE which seems too large to links these two events.


The nature of the onset of the Younger Dryas appears to be identical to the termination of Dansgaard Oeschger events.

The Bølling Allerød events and Dansgaard Oeschger events show up in multiple isotope proxies of the ice cores and ocean drilling project (ODP) cores. The most compelling comparison can be made using deuterium excess of the GISP ice core (Masson-Delmotte et al., 2005). Deuterium excess is a very sensitive proxy and the similarity between the Dansgaard Oeschger events and the Bølling Allerød is striking. Hence, the chance is remote that an ETE triggered other events that resulted in exactly the same deuterium excess fingerprint at the termination of the multiple Dansgaard Oeschger events. Instead, this matching fingerprint strongly suggests that all of these events share the same as-yet-unknown cause or causes for its onset and termination, found in irregular millennial scale cycle changes in moisture source. A good candidate may be changing flows of the Thermohaline Current.

The extent of megafaunal extinction exceed single location and single date

The global megafauna extinction during the Late Pleistocene appears to have accelerated significantly in Alaska around 15 ka Cal BP (Guthrie 2003) with the disappearance of horses, and may have terminated around 4,000 Cal BP with the definite extinction of the woolly mammoth on Wrangel Island (Vartanyan et al., 1995). Channel Islands (Agenbroad, 1998), and Pribilof islands (Crossen, 2005). Furthermore, the extinctions also deviated from species to species. Ground sloths (Steadman et al 2005) disappeared in the Americas asynchronously, spanning the Younger Dryas. Meanwhile, Straight-tusked elephants and woolly mammoths disappeared in Europe, clearly before the onset of the Younger Dryas (Stuart 2005). In contrast, American mastodons (Miller 1987, Polaco et al., 2001 ) and the Irish Elk (Stuart et al., 2004) survived on the Eurasian continent until well into the Holocene. Also, modern species like the American bison, elk and deer survived the ETE, which suggest that the impact on the species may have been limited, and given the extent of the extinction, its contribution to the mass extinction event may be overrated.

Conclusions.

It is clear that the evidence of Firestone et al., 2007 suggest unusual occurrences in the terminal phase of the Allerod event. It may very well explain the sudden disappearance of the Clovis but the assumed link with the Younger Dryas and the megafauna extinction may be too ambitious. The ETE precedes the actual onset of the isotope Younger Dryas considering the bulk of the high resolution evidence. Furthermore, the records of multiple proxies, especially the deuterium excess of the GRIP ice core strongly suggest identical causes for the onset and termination of all Dansgaard Oeschger events as well as the Bolling Allerod events. However, there is only one ETE. Finally, on a global scale, the extinction of the megafauna happened rather gradually before and after the ETE, while some local megafauna species appear to have survived it. Therefore linking the ETE to the Younger Dryas and the megafauna extinction appears to be unsupportable.


References

Agenbroad, L. 1998. Pygmy (Dwarf) Mammoths of the Channel Islands of California. Mammoth Site of Hot Springs, SD, Inc.

Crossen K.J. 2005 GSA Meeting Salt Lake City Abstracts with Programs, Vol. 37, No. 7, p. 463 (http://gsa.confex.com/gsa/2005AM/finalprogram/abstract_97313.htm )

Firestone R.B. et al 2007; PNAS 104/ no 41 pp 16016-16021

Goslar et al. 1995. Nature, 377: 414-417.

Grafenstein U von, et al, 1995 Science 284, 1654-1657.

Grootes, P.M., and M. Stuiver. 1997. Journal of Geophysical Research 102:26455-26470

Guthrie, R.D 2003 Nature 426, 169-171 (13 Nov)

Johnsen, S.J et al 1997. Journal of Geophysical Research 102:26397-26410.

Lücke, A. Brauer A., 2004. Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 211, Issues 1- 2, 19 August.

Masson-Delmotte et al 2005. Science 1 July 2005: Vol. 309. no. 5731, pp. 118 - 121

Miller W.E. 1987 Journal of Paleontology, Vol. 61, No. 1, pp. 168-183

North Greenland Ice Core Project members. 2004 Data Contribution Series # 2004-059. NOAA/NGDC Paleoclimatology Program, Boulder CO, USA.

Reimer P, et al 2004. Radiocarbon (Volume 46, nr 3).

Polaco et al 2001, proceedings first international congress of the World of Elephants 2001 Rome pp 237 - 242

Steadman DW et al 2005; PNAS August 16, vol. 102 no. 33 11763–11768

Stuart, A.J., 2005. Quaternary International, Volumes 126-128, 2005, Pages 171-177

Stuart A.J et al 2004 Nature 431, 684-689, 7 October

Stuiver M, et al 1998. Radiocarbon 40(3):1041–83.

Vartanyan, S.L., et al 1995. Radiocarbon 37: pp.1-6.

Zolitschka, B., et al 2000 Geology, 28/9, 783-786.

Any questions?

 

[Andre]

(necropost) Meanwhile it looks like the comet lost its sparkle.

...In sedimentary deposits dating to the beginning of the YD, impact proponents have reported finding carbon spherules containing tiny nano-scale diamonds, which they thought to be created by shock metamorphism or chemical vapor deposition when the impactor struck...

In the August 30 issue of the Proceedings of the National Academy of Sciences, a team of scientists led by Tyrone Daulton, PhD, a research scientist in the physics department at Washington University in St. Louis, reported that they could find no diamonds in YD boundary layer material...

...Instead, graphene- and graphene/graphane-oxide aggregates were found in all the specimens examined (including carbon spherules dated from before the YD to the present). Importantly, the researchers demonstrated that previous YD studies misidentified graphene/graphane-oxides as hexagonal diamond and likely misidentified graphene as cubic diamond...

 

[Andre]

Another necropost (but the previous posts have not lost any significance).

While the impact idea waned, several scholars pursue an extraterrestrial event of another kind, solar activity.

Paul A. LaViolette (2011) Evidence for a Solar Flare Cause of the Pleistocene Mass Extinction, February 18, 2011. Radiocarbon, vol. 53, No. 2 (June 1, 2011): 303 - 323

Abstract

The hypothesis is presented that an abrupt rise in atmospheric radiocarbon concentration evident in the Cariaco Basin varve record at 12,837±10 cal yrs BP contemporaneous with the Rancholabrean termination, may have been produced by a supersized solar proton event (SPE) having a fluence of ~1.3 X 10^11 protons/cm2. A SPE of this magnitude would have been large enough to deliver a lethal radiation dose of at least 3 - 6 Sv to the Earth's surface, and hence could have been a principal cause of the final termination of the Pleistocene megafauna and several genera of smaller mammals and birds. ...cont'

I also recommend reading http://sd.ddns.us/science/article/pii/S1040618211001480 of an author who is well known to some of us

There are however other devellopments on which I will report later that give some substantiation to Richard Muller's favorite quote of Josh Billings:

The trouble with people is not that they don't know, but that they know so much that ain't so.

 

[Andre]

Notice that Laviolette (2011) builds his case around a 14C carbon spike in the atmospheric CO2 around 12900 years ago that correlates with the onset of the Younger Dryas.

Notice the dating problems mentioned in the OP:

The dating gap of the onset of the Younger Dryas exceeds the error margin

Based on two series of carbon dates which mark the end of the Clovis stratum, Firestone et al. establish the dating of the ETE at 12.9 +/- 0.1 ka Cal BP. This date is cross-checked with the onset of the Younger Dryas in the Greenland GISP-2 ice core marked by a sharp drop of water isotopes.

These carbon date series, averaging 10,890 14C years and 10,940 14C years BP, would calibrate to 12.87 and 12.88 ka Cal BP using the INTCAL04 calibration table (Reimer et al., 2004) while the article mentions 12.92 and 12.93 ka Cal BP, which is likely based on the previous INTCAL98 calibration table (Stuiver et al., 1998)...

...The most accurate dating may be found by counting lake varves and correlating these to several well-dated tephra layers (Zolitschka et al., 2000). The records of the Meerfelder maar (Lücke and Brauer, 2004), Lake Gosciaz, (Goslar et al., 1995), the Ammersee (von Grafenstein et al., 1995) closely follow the GRIP ice core chronology. Hence, high resolution records independently reproduce an onset of the isotope Younger Dryas at around 12,675 +/- 25 varve years BP, (see http://www.gfz-potsdam.de/pb3/pg33/p...aar/index.html ) which is more than two sigma outside the error range of the date of the ETE which seems too large to links these two events.

Finally notice also that Fiedel (2011) in the previous post recognises this dating problem and mentions for calibration purposes a new calibration table INTCAL09.

Would a comparison of the calibration tables INTCAL04 and INTCAL09 shed some light on these issues?

I wondered that too and the result was ...erm, remarkable. I think that is worth a separate thread.

Oh if anyone wants to have the cited papers for scrutiny, please pm me.

 

[Andre]

After some consultation, it may be better to keep the narration in this thread, but I need to elaborate on carbon dating techniques and calibration to demostrate how and why things went wrong here with the extrateresstrial hypothesis, the 14C spike and the dating of the lower (older) Younger Dryas boundary.

Now you could read the wiki about carbon dating which is excellent or take it to the detailed level with http://researchcommons.waikato.ac.nz/bitstream/10289/3622/1/Hogg%20Intcal09%20and% . But let me elaborate about that in the next post.

 

[Andre]

Okay so a quick overview of carbon dating then, which is based on the amount of nuclear unstable carbon-14 with a half value time around 6000 years.

Carbon-14 is produced due to interaction of cosmic rays in the atmosphere in which neutrons interact with 14Nitrogen atoms as follows:

[URL]http://upload.wikimedia.org/math/5/2/f/52f20ea2f25b231f49d14690009d67a6.png[/URL]

The 14C oxidizes and mingles with the atmospheric CO2 entering the carbon cycle. As the 14C decays again with time, the ratio of 14C to normal 12C decreases and this says something about the age of the mechanism. If the starting ratio was constant, dating would have been rather simple

However since these processes are highly variable we do not know the initial 14C/12C ratio. So we would need to calibrate the dating with something that can both be carbon dated and dated otherwise.

Far out the best calibration is done with things that due have some annual accumulation; tree rings, annually layered deposits in deep lakes (varves), speleothems and coral.

Of these tree rings are the most accurate as the 14C changing processes are the simplest, the wood is made directly from atmospheric CO2 and can obviously be carbon dated directly. The problem however is that good treering assemblies go only back as far as about 12,500 years

Annual lake varves can also be counted very accurately, the problem is that it does not contain a lot of carbon datable macro fossils.

annual Speleothem- and Coral rings can also both be counted and carbon dated (carbonates), however there is also a problem here as the carbon is not directly coming from the atmosphere.

That's where the biological fertilizer comes in contact with the rotating vanes of a machine that produces a high speed low pressure airflow.

More later

 

[Studiot]

I am reading and taking all this in - honest

So thanks for posting.

 

[Andre]

Thanks for the feedback. I appreciate that greatly. I'm just trying to illustrate where certain parts of Earth science stands now and how important it is to try and think of everything that can affect the 'whodunit'-reconstruction.

Anyway, to get back to the problems with coral or any marine carbon dating, it's the mixture of carbon sources. For air sources we don't mind a few weeks or even years between the formation of the 14C in the higher atmosphere and the time it got fixed by photosynthesis, entering the biologic part of the carbon cycle. But for the sea/ocean is different. Some carbon did indeed enter the water recently but it is mixed with dissolved carbonates that have been in the water for a long time, like dissolved limestone etc, and hence depleted from 14C, decreasing it's ratio. This is called the "basin effect".

Now if you have overlapping calibration series of land and marine data, you can calibrate the basin effect (calibrate the calibration) and it is found in some instances that the basin effect is rather constant and amounts for a few hundred years carbon dating.

But if you find a couple of instances where this is true, is it also always true?

 

[Dotini]

Fascinating investigation of a good mystery, Andre. I've been interested in this for a long time, ever since I marveled at the saber-tooth tigers of the La Brea tar pit museum, so I appreciate your posts very much.

If there was a super-CME which wiped out megafauna in the Americas, how might it be that the megafauna of Africa were spared?

Respectfully,
Steve

 

[Evo]

I also recommend reading http://sd.ddns.us/science/article/pii/S1040618211001480 of an author who is well known to some of us

Finally notice also that Fiedel (2011) in the previous post recognises this dating problem and mentions for calibration purposes a new calibration table INTCAL09.

Is there anything you would like me to ask Stuart?

 

[Andre]

Is there anything you would like me to ask Stuart?

Maybe advise him to take note of this thread. There is an issue coming up with his paper. Maybe, we could have a good discussion.

 

[Andre]

If there was a super-CME which wiped out megafauna in the Americas, how might it be that the megafauna of Africa were spared?

Respectfully,
Steve

Excellent question Steve, One could probably to electromagnetic cosmic influence to be redirected towards the poles like the aurora borealis and aurora australis, but I don't think there is a reason for such audacities.

Anyway, to continue, as I said earlier

... Would a comparison of the calibration tables INTCAL04 and INTCAL09 shed some light on these issues?

I wondered that too and the result was ...erm, remarkable...

So having some carbon dating calibration back ground now, it's maybe time for the wow.

data sets: Intcal09, Intcal04.

Been busted once for making my own graphs, but nobody else does it, so I take that risk:

Ideally, both graphs should overlap with only tiny abbarations, but the difference in our time frame of interest is huge, notice that the calibration of ~10,900 14C years, the approximate boundary of the Younger Dryas, (yellow line) used to calibrate roughly to something like 12,870 calendar years BP with Intcal04, but it calibrates now, with Intcal09, to something like 12720 Calendar years.

That is major and far fetching, but why is that so?

 

[Andre]

Oh, before we concentrate on the why, remember that Laviolette (2011) mentions a radio carbon spike in this time frame:

The hypothesis is presented that an abrupt rise in atmospheric radiocarbon concentration evident in the Cariaco Basin varve record at 12,837±10 cal yrs BP contemporaneous with the Rancholabrean termination, may have been produced by a supersized solar proton event.

We see in the intcal data sets linked to in the previous post that there is also a column "Delta 14C permil". That looks like the ratio of radiocarbon. So we can plot that too for both Intcal tables:

Sure enough Intcal04 shows a significant radiocarbon spike corresponding with the mentioned Caracio Basin varve record, but look what happened with Intcal09. It's gone, only a little spike remains, hardly outstanding against other local spikes, but some 250 years later.

That is even more far fetching.

 

[Andre]

So for the why question, we need to scrutinize the original publication Reimer et al 2009. (I see that I mutilated the earlier link in my previous post yesterday and it doesn't work, but nobody noticed What is that guys? Don't you care reading the science behind all this? )

Anyway considering this discrepancy we just discovered, Reimer et al write:

(p1116) OTHER NEW DEVELOPMENTS

There is growing evidence that the western subtropical Atlantic reservoir age was much less than the modern ~420-yr offset during the early Younger Dryas (~12,550–12,900 cal BP)(Kromer et al. 2004; Muscheler et al. 2008; Singarayer et al. 2008)...

...While we could, in theory, calculate a time-dependent reservoir correction for the marine data, it was decided instead to exclude the western subtropical Atlantic marine data for the early Younger Dryas period ~12,550–12,900 cal BP...

(p1117)
Foraminifera from the Cariaco Basin varved sediments (Hughen et al. 2004a) were used as in
IntCal04 with the exception of measurements from 12,552–12,944 cal BP, which are likely to be affected by marine surface reservoir age changes associated with the onset of the Younger Dryas as previously discussed.

But the result of that decision is far fetching

 

[lisab]

Thanks for the feedback. I appreciate that greatly. I'm just trying to illustrate where certain parts of Earth science stands now and how important it is to try and think of everything that can affect the 'whodunit'-reconstruction.

Anyway, to get back to the problems with coral or any marine carbon dating, it's the mixture of carbon sources. For air sources we don't mind a few weeks or even years between the formation of the 14C in the higher atmosphere and the time it got fixed by photosynthesis, entering the biologic part of the carbon cycle. But for the sea/ocean is different. Some carbon did indeed enter the water recently but it is mixed with dissolved carbonates that have been in the water for a long time, like dissolved limestone etc, and hence depleted from 14C, decreasing it's ratio. This is called the "basin effect".

Now if you have overlapping calibration series of land and marine data, you can calibrate the basin effect (calibrate the calibration) and it is found in some instances that the basin effect is rather constant and amounts for a few hundred years carbon dating.

But if you find a couple of instances where this is true, is it also always true?

I'm a noob on this topic, but that 'basin effect'...I'm not getting a lot of info on that term. I tried looking up 'lake effect' but that's a meteorological term about snow formation.

 

[Andre]

Right Lisa, good catch, my bad. Mea culpa. I meant to say 'reservoir effect', the same mentioned as 'reservoir age' in Reimer et al:

There is growing evidence that the western subtropical Atlantic reservoir age was much less than the modern ~420-yr offset during the early Younger Dryas ...

So there is the whole problem, changes in the ocean flows, whcih were disrupting the expectation that the reservoir effect caused a more of less constant age different. But this assumption produced a spurious 14C spike that sent future researchers on a tangent in an attempt to explain that. Hence LaViolette 2011 loses it's principle cause, no more big radiocarbon spike at the onset of the Younger Dryas.

“The great tragedy of Science: the slaying of a beautiful hypothesis by an ugly fact”.

Thomas Huxley

Obviously we can also say something more about the timing of the mysterious onset of the Younger Dryas now next.

 

[Andre]

Anyway, that decision in Reimer et al (2011) keeps bugging me:

...While we could, in theory, calculate a time-dependent reservoir correction for the marine data, it was decided instead to exclude the western subtropical Atlantic marine data for the early Younger Dryas period ~12,550–12,900 cal BP...

If a scientist 'could, in theory,' solve a problem, he will, I would think. Moveover it would be pretty important to know the reservoir age devellopment. So why not here?

It gets more intruging if you look at the graphs of the original Hughen et al 2000 in science, particurly the line up with the Younger Dryas in the GISP2 icecore, also showing the -now- spurious 14C spike.

http://www.ncdc.noaa.gov/paleo/pubs/hughen2000/fig4.jpg

This has always looked like a pretty solid base to establish the onset of te Younger Dryas at 12,900 Cal years BP. But now these data between "12,552–12,944 cal BP' are essentially voided by that decision.

 

[Andre]

I promissed issues wth Fiedel (2011):

...
I also recommend reading http://sd.ddns.us/science/article/pii/S1040618211001480 of an author who is well known to some of us ...

I observe that his analysis is accurate most of the time, except however.., and maybe I may quote the following:

..In Meerfelder Maar, a German crater lake, the wind strength changed abruptly and permanently during the winter of 12,679 cal BP, marking the local onset of the Younger Dryas (Brauer et al., 2008). This date is based on counted varves that are explicitly tied to the GRIP chronology, which has now been superseded by NGRIP; accordingly, it should be corrected to ca. 12,850 cal BP..

I don't understand the boldface (mine). The orginal dating of the periglacial oscilations is publiced in Brauer et al (2001) Lateglacial varve chronology and biostratigraphy of lakes Holzmaar and Meerfelder Maar, Germany Boreas 30 pp 83 - 88. There is no mentioning of any ice core in that publication, just the correlating of the varve stratigraphy without external calibrations and it finds for the Younger Dryas 11 590–12680 varve years BP in the Meerfelder maar and for the Holzmaar, 11600–12 606 varve years, independently of any other dating. The difference is discussed.

----

Fiedel then mentions multiple research results, including the 14C spike problems, all suggesting that the onset of the Younger Dryas -in Europe- was around 12,700, but nevertheless he concludes:

Are the disparities among ice and lake sediment cores a matter of 1) counting mistakes, whether caused by human error, instrument problems, or erratic deposition; or 2) reliance on different aspects of the environment, atmosphere, and chemistry to define the events of interest? I suspect that the GISP2 and Cariaco counts eventually will prove most accurate and the YD onset date was about 12,830 -12,980 cal BP.

Unfortunately, with the deletion of exactly those Cariaco data in INTCAL09, much of the substantiation for that assessment has disappeared.

 

[Andre]

Anyway, the Cariaco problem keeps bugging me. This is what http://www.nature.com/ngeo/journal/v1/n4/full/ngeo128.html (Cited by Reimer et al 2009) propose:

(Abstract)...Here we discuss a radiocarbon chronology from a tree-ring record covering the Late Glacial period that has not been absolutely dated. We correlate the chronology to ice-core timescales using the common cosmic production signal in tree-ring 14C and ice-core 10Be concentrations. The results of this correlation suggest that the Cariaco record may be biased by changes in the concentration of radiocarbon in the upper ocean during the early phase of the Younger Dryas climate reversal in the Cariaco basin. ...

While Hughen et al (1998) found originally:

Direct evidence for a stable Cariaco Basin reservoir age through time is seen in the close match between tree-ring and Cariaco Basin 14C ages from 10.0-11.8 cal kyr BP (Figure 3). The reservoir age remains the same, within errors, during a period of almost 2000 years. More importantly, the reservoir age remains constant across the large change in upwelling at the Younger Dryas termination. This climate shift, representing one of the largest transitions in the Cariaco Basin record between periods of intense and reduced upwelling, occurred in less than a decade. Cariaco Basin 14C dates overlap with the tree-ring radiocarbon record immediately prior to the Younger Dryas-Preboreal transition (Figure 3). If variable upwelling had influenced reservoir age, we would expect to see it here. However, there is no discernible shift to older 14C ages in Cariaco Basin dates during the Younger Dryas.

But maybe we are looking at the wrong problem. As Fiedel (2011) sums up, there exist several annually counted geologic records for the whole younger dryas. European lake varve records and the GRIP ice core tend to count ~1050 years, whereas the GISP-II ice core and the Cariaco basin foraminifera varves counted ~1300 years. So maybe it is not a reservoir age problem but a year counting problem?

 

[Andre]

That counting problem could be supported by the work of the Polish Quartenary geologist Tomas Goslar in Goslar et al 1999, Variations of atmospheric 14C concentrations over the Allerod-Younger Dryas transition, Climate Dynamics (1999) 15 : 29Ð42

It compares the carbon dating versus annual varve counting of the Swedish lake Madtjarn and the Polish lake Gosciaz
(Sorry Borek, my keybord does not produce all those random outcrops on the letters) against marine counts of corals and sure enough the Cariaco basin.

The caption:

Fig. 3 Radiocarbon ages versus calendar-year ages during the Late Weichselian and early Holocene. The records of Lake Gosciaz (solid circles) (Goslar et al. 1995a) and the Swedish varved clays (open diamonds) were synchronised by the method described in the text. Open triangles represent the 14C-U/Th dates on corals from Barbados
and Mururoa Atoll (the calculated mean) (Bard et al. 1993), Huon Peninsula (Edwards et al. 1993) and Tahiti (Bard et al. 1996). Crosses denote 14C dates derived from varved sediments from the Cariaco Basin (Hughen et al. 1998). All data sets are presented with
a double standard deviation. The smooth line represents a spline function plotted to all the data, except to those from the Cariaco Basin...

The area of interest is obviously the red oval where the spline function goes down steeply while the Cariaco crosses go almost horizontal. I guess that could have been the hypothetical result if the Cariaco varves count was too high.

Notice also that Goslar et al place the older Younger Dryas boundary around 12650 Cal year BP.

But the Cariaco chronology was selected for the INTCAL tables while the other were not. It's a choice I guess. But objective?

 

[Andre]

I realize that the focus of the thread has shifted from the extraterrestrial event itself to it's alleged dating, giving an interest gap of some 200 years. I did not mention another interesting feature that also strongly supports the later date for the beginning of the Younger dryas and that is the gigantic eruption of the Laacher See maar type volcano which ejected many cubic km of material into the atmosphere, that eventually formed an uniformly aged widespread layer known as the Laacher See tephra, which can be used to calibrate dating, the tephrochronology

The general consensus via multiple dating is that the eruption took place 12,900 years ago hence the article in wiki (erronously) reads:

The Laacher eruption coincides with the onset of the abrupt Younger Dryas re-glaciation, which brought renewed very cold conditions to the northern hemisphere from 12.9 to 11.6 ka.

No..no..no wrong. Reason why you never can trust wikipedia. It's as good as whoever wrote it. Take any scientific publication mentioning both the onset of the Younger Dryas and the Laacher see and it will telll that the Laacher See erupted some ...200 years earlier. Again! 200 years. The most accurate report is from the lake layer (varves) counting in the Eifel for instance from Lucke and Brauer 2004 - see OP. But also http://www.wsl.ch/staff/felix.kaiser/PDFs/Kromer_etal.2004.pdf on page 1205 (3) mention that under "absolute placement of the pinechronology..."

Notice however that Kromer et al do not mention the exact date of the Laacher see eruption, while they adhere to the erronous 12.900 bp date for the onset of the Younger Dryas, comparing it with the Cariaco basin grey scale.

So what was that exact date for the eruption? 11,063 +/- 12 carbon years dated from then living trees in situ buried by the volcanic ash, see this. So both the INTCAL04 and INTCAL09 would transfer that to some 12940 cal years BP, however THE Laacher see specialist, Felix Riede http://www.sciencedirect.com/science/article/pii/S0305440307001008. Fine with me. What is 20 years in between friends.

But we still have to apply that 200 years between the onset of the Younger Dryas and the eruption, which would bring us -via another completely independent way- to 12,720 years BP. Remember that Lucke and Brauer counted to ~12,680 with a one procent error. I guess we can live with that 40 years.

However with that overlooked/ignored(?) 200 years problem, the discussion of Kromer et al 2004 gets a completely different dimension. I have to OCR that paper somehow for quotes.

 

[NileQueen]

Yes what else might be hidden in the Laacher see tephra? Haynes reports an elk. That's very interesting.

 

[MrGamma]

Ideally, both graphs should overlap with only tiny abbarations, but the difference in our time frame of interest is huge...

It looks interesting, is it a mistake based on the way they took the measurements inaccurately from one time to the next? Or is a something to do with the differences in methods used to collect the data and how each method might be prone to a different result?

I don't understand the thread in its entirety, I am just asking in hopes to understand it a little more. In any event, when you say these are isotope levels, is that synonymous with "radio carbon" levels?

People have theories that cold periods might be due to lack of sun spot activity. Does isotope levels relate to that in any way, or is this something entirely different? Hope this not bothersome. You just have a really good understanding of this. (I have never heard the term Younger Dryads till today)

 

[Andre]

It looks interesting, is it a mistake based on the way they took the measurements inaccurately from one time to the next? Or is a something to do with the differences in methods used to collect the data and how each method might be prone to a different result?

That's a good question, Earth science is akin to forensic science, all about causalities, but which caused what or was it the other way around or was it something else. Hence, the biggest problem is the inherent unavoidable affirming the consequent fallacy

Obviously for causality dating is extremely important - what came first - and the many different ways of dating events are compared constantly, usually with satisfactory results. However, it's also possible that some erroneous results are assumed to be right and may propagate to other chronologies, which are calibrated/adapted to the wrong one. Maybe that caused the two camps for the start of the Younger Dryas, 12,900 cal BP versus 12,700 Cal BP.

So the counters of the annual sedimentation layers of the Caracio basin counted 200 layers too many maybe? or maybe they corrolated it to other chronologies like the GISPII ice core, firmly assuming it to be right. Only they can tell and there could be other explanations as well.

I don't understand the thread in its entirety, I am just asking in hopes to understand it a little more. In any event, when you say these are isotope levels, is that synonymous with "radio carbon" levels?

That graph shows the calibration tables to calibrate the calculated 14C age to real age, which is based on the remaining radioactive 14C isotopes in the sample. Maybe that this wiki is clear on that, but if not I'll try to explain more.

People have theories that cold periods might be due to lack of sun spot activity. Does isotope levels relate to that in any way, or is this something entirely different?

It's all sort of related. Many isotope fractination processes, like water evaporation and condensation are temperature dependent, so if isotope ratios in precipitation, for instance 18O versus 16O, change with time, one could conclude that this is caused by temperature. However, here is the affirming the consequent fallacy again: (a causes b, we see b hence it was caused by a). But isotope ratios can also change due to other circumstances but that would go OT.

Hope this not bothersome.

No, on the contrary, it's fine. thanks for the feedback. Essentially it's my fault if it was all incomprehensable, and hence the thread would be useless then. My intention is merely to show the complexities and uncertainties in Earth science and how difficult it is to keep on the straight and narrow of the scientific truth.

 

[Andre]

Anyway Baales et al 2002 give a most excellent exposition of the Laacher See volcanic event and their analysis of the Younger Dryas dating problem agrees roughly with mine. Obviously they were first. By combining different data and techniques they find that the eruption took place in the late spring of 12,916 Cal years BP and...

Taking this date as the “zero year” of late glacial archives for this specific point, the GRIP record has to be shifted by 23 yr to an older age, while the GISP2 record has to be shifted by 121 yr to a younger age.

The different annual countings between the Laacher See Tephra layer and the onset of the Younger Dryas averages 205, so that would get to a start for the Younger Dryas of 12,711 Cal years BP plus a certain eror margin of course.

I wonder about the validity of using erroneous records to get to that average.

 

[Nik_2213]

At least the tephra and ice-core layers are related. Hopefully, the eruption was sufficiently singular, rather than extended. It would not do to have timber washed into the lake after laying for indeterminate time(s) en-route...

 

[MrGamma]

So the counters of the annual sedimentation layers of the Caracio basin counted 200 layers too many maybe? or maybe they corrolated it to other chronologies like the GISPII ice core, firmly assuming it to be right. Only they can tell and there could be other explanations as well.

So guessing that an ice core can contain layers of a vastly different mass when compared to sedimentary basin rock and it is calibrated correctly.

Would isotope levels in the rock be a different result, compared to the ice core due to the geography of the land? Perhaps the sedimentary rock was run off from a mountain where radio carbon was swept down to a basin and collected, increasing in volume? While the ice core was just steady precipitation? Or perhaps the ice core is different due to an uneven precipitation?

By combining different data and techniques they find that the eruption took place in the late spring of 12,916 Cal years BP and...

I do trust that professionals are doing the work correctly or to the best available methods, my real question is just trying to understand the difference in the results. Is it an indication of something significant or unknown, or is it easily explainable by another means? Sorry... I am not up to speed obviously.

 

[Andre]

At least the tephra and ice-core layers are related. Hopefully, the eruption was sufficiently singular, rather than extended. It would not do to have timber washed into the lake after laying for indeterminate time(s) en-route...

I believe that maar-type explosive eruptions are believed to be singelar.

Also if older timber was used to date the event, obviously we would date only the timber and that would make the eruption even younger, farther away from the original assumptions. However I believe that Baales et al 2002 mention that dating is done on in situ buried standing trunks.

 

[Andre]

.

These questions require some elaborations, unfortunately I am helping relatives move so I get bac to that later.

 

[Andre]

Anyway, yes let's talk ice cores. Obviously the difference between the different Greenland ice cores (DYE-3, GRIP, GISP-II and NGRIP) especially considering the Younger Drays boundaries was reason for a thorough investigation, resulting in a new Greenland Ice Core Chronology 2005 (GICC05) http://www.gfy.ku.dk/~www-glac/papers/pdfs/220.pdf.

The result is rather remarkable, in table 4 (page X-12) the date ("Age B2K") of 12,896 years +- 138 is given. B2K is obviously before 2000AD, while the conventional "BP' - Before Present means before 1950AD. Hence we are looking at 12,846 years BP. Are we back to the 12.9 Ka Boundary? Certainly a very interesting development inviting a more thorough look.

 

[Dotini]

Anyway, yes let's talk ice cores.

Andre, is it conceded that ice core records can be muddled by layers formed during a season of melts/refreezing due to weather events?

Respectfully,
Steve

 

[Andre]

Sort of, Rasmussen et al are explaining elaborately about the uncertanties of what constitutes a year. One needs to read the paper in toto especially part 4, identification of annual layers. They use several proxies in order to find back an annual signal and provide an optical example (fig 3) that seems to be okay. However, in how many cases there was doubt is not really clear.

What is clear however is that Rasmussen et al do not waste a single word comparing their timescale with the milestones to other chronologies. That's where it gets very interesting.

More later.

 

[Andre]

The first check that Rasmussen et al could have done is verifying the dating of another most important volcanic tephra layer, the Vedde Ash. It has been radiocarbon dated extensively to an average of 10,310 +/- 50 14C years

Calibrated with Intcal09 this gives a range of 12,039 - 12,137 Cal BP

Rasmussen et al count the Vedde Ash in table 4 on 12,121 Cal BP (12.171 B2K) +/- 114 years hence a range of 12,007 - 12,235 years Cal BP. We see that both ranges overlap nicely abeit that Rasmussen puts the mean weight a few decades later.

Next we could also compare the onset and termination of the Younger Dryas as summarized by Baales et al 2002 in table 4 (p285) with the timescale of rasmussen, GICC05:

See for caption Baales et al 2002, note that the dating in there for GISP-II (Alley et al., 1993) and GRIP (Johnsen et al., 1992) are early versions, superseded later. The lower two rows are depicting the dating of the Younger Dryas, based on their layer counting between the Laacher See Tephra and the onset of the Younger Dryas and then the termination, by adding the counted duration of the YD. Note that Brauer et al 1999, (in the column "MFM*") the only varve layer counting chronology from year zero, arrives at a slightly younger age.

Now see that all proxies agree closely to the termination of the Younger Dryas, only a few years away from the average of 11,570 years Cal BP. Rasmussen et al, (GICC05) however are now way off, all of a sudden with 11,653 years Cal BP, the difference increasing at the onset of the Younger Dryas all records being generally well within two decades of 12,712, against 12,846 for GICC05.

Seems indeed that some scrutiny would be in order.

 

[Andre]

Meanwhile, resurrecting the thread, due to a new publication,

http://www.pnas.org/content/early/2012/06/14/1204453109.full.pdf

Abstract

It has been proposed that fragments of an asteroid or comet impacted Earth, deposited silica-and iron-rich microspherules and other proxies across several continents, and triggered the Younger Dryas cooling episode 12,900 years ago. Although many independent groups have confirmed the impact evidence, the hypothesis remains controversial because some groups have failed to do so. We examined sediment sequences from 18 dated Younger Dryas boundary (YDB) sites across three continents (North America, Europe, and Asia), spanning 12,000 km around nearly one-third of the planet. All sites display abundant microspherules in the YDB with none or few above and below. In addition, three sites (Abu Hureyra, Syria; Melrose, Pennsylvania; and Blackville, South Carolina) display vesicular, high-temperature, siliceous scoria-like objects, or SLOs, that match the spherules geochemically. We compared YDB objects with melt products from a known cosmic impact (Meteor Crater, Arizona) and from the 1945 Trinity nuclear airburst in Socorro, New Mexico, and found that all of these high-energy events produced material that is geochemically and morphologically comparable, including: (i) high-temperature, rapidly quenched microspherules and SLOs; (ii) corundum,mullite, and suessite (Fe3Si), a rare meteoritic mineral that forms under high temperatures; (iii) melted SiO2 glass, or lechatelierite, with flow textures (or schlieren) that format >2,200 °C; and (iv) particles with features indicative of high-energy interparticle collisions. These results are inconsistent with anthropogenic, volcanic, authigenic, and cosmic materials, yet consistentwith cosmic ejecta, supporting the hypothesis of extraterrestrial airbursts/impacts 12,900 years ago. The wide geographic distribution of SLOs is consistent with multiple impactors.

The article is very elaborate and puts the ball back in the field of the sceptics. One can follow the dispute on wiki.

I repeat my take, since, as far as I know, the complete fingerprint of the Younger Dryas in all proxies (like the ice cores - including deuterium excess, but also in oceanic sediment cores) is about equal to the fingerprints of the Dansgaard Oeschger (D-O) events, it's hard to see why we need impacts to cause that, where the D-O events did without.

Nevertheless impacts do happen, and I'm more than happy to accept that there was/ were (multiple) impact(s) at the onset of the Younger Dryas, the problem is that cause and effect may be a lot more complicated.