Extraterrestrial impact kills megafauna?

Andre

I promissed issues wth Fiedel (2011):

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

I dont 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.

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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:

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 Muscheler et al (2008) (Cited by Reimer et al 2009) propose:

While Hughen et al (1998) found originally:

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:

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:

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 Kromer et al 2004 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 determines 12,920BP. 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

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

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.

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.

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.


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...


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 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?

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

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) Rasmussen et al, 2006 (draft here).

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

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,

Bunch TE, Hermes RE, Moore AM, et al. (June 2012). "Very high-temperature impact melt products as evidence for cosmic airbursts and impacts 12,900 years ago". Proc Natl Acad Sci U S A 109 (28): E1903–12. doi:10.1073/pnas.1204453109. PMID 22711809.

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.