There was a paper in Science last week that has gotten quite a bit of press. It reports further evidence in support of the idea that the Younger Dryas — a distinct period towards the end of the last ice age when the deglaciation in the Northern Hemisphere was interrupted for a period of about 1300 years — was caused by a barrage of comets hitting North America.
When the first papers on this came out last year, we expressed skepticism. We remain skeptical and our reasons remain unchanged. But we think it is worth saying a bit more on this, because the reporting on this issue has largely ignored just how big an idea this is, and therefore how much more work would need to be done before it could be taken very seriously.
For background, see the good article by Kenneth Chang in the New York Times, which, however, does not address our main concerns with the hypothesis.
The brief history is that in 2007, Firestone and others published an article in PNAS showing evidence of various materials that may be diagnostic of extraterrestrial origin (and hence an impact) in layers of sediment dating to 12.9 thousand years ago, just before the beginning of the Younger Dryas cold event. Now, in a Brevia piece in Science Kennett and others show further evidence: “abundant nanodiamonds in sediments dating to 12.9 ± 0.1 thousand calendar years before the present at multiple locations across North America.”
According to Richard Kerr’s news item that accompanies the article in Science, at least some experts are skeptical that Kennett and others have really found nanodiamonds, or that, even if they have, they are necessarily evidence of an impact. But we don’t claim enough expertise in nanodiamond detection or interpretation to have an opinion on this aspect, so let’s give them the benefit of the doubt. Suppose there really was an impact (or impacts) at the right time in the right place. We’d still be skeptical that this was a trigger for the Younger Dryas.
Among our reasons for skepticism (again, see our earlier post on this) there is a basic statistical problem. The problem is — and this context is missing from most if not all of the articles we’ve seen on this — that explaining the Younger Dryas in terms of an impact leaves all the other rapid climate change events (the so-called “Dansgaard-Oeschger events”) of the last glacial period unexplained.* One would have to either accept the conventional ideas for the causes of these events, or, alternatively, one would have to propose that there was an impact not only before the Younger Dryas, but before each of the earlier events.
We recognize that it isn’t entirely an either/or situation. Indeed, the suggestion appears to be that a cometary barrage causes various kinds of havoc, including the ice sheet collapse that led to ocean circulation change (the most well-evidenced proximal cause of rapid climate change). But the point is that if these events can happen as part of the inherent variability of the ocean-atmosphere-ice-sheet system, then there is no need to invoke the impact hypothesis in the first place. And indeed it would be virtually impossible to show it was other than mere chance that comet impacts occurred at the right time, especially given that it would still be necessary to show that the ice sheet would care about comets, which we also consider unlikely (see the good discussion — particularly Mauri Pelto’s comments — on this over at the Open Mind Blog). On the other hand, if abrupt climate changes don’t happen on their own — if they only happen due to extraterrestrial causes — then one would want to see evidence of impacts for at least a few more of them, not just one. That would be a truly exceptional paradigm-breaking discovery, going against just about everything we think we know about the system.
We emphasize that we are not saying “the Younger Dryas can’t have been caused by a comet, unless all the Dansgaard-Oeschger events were caused by comets”. We’re saying that we see no need to invoke such an hypothesis, so the level of proof required for this extraordinary idea will need to be extraordinarily strong. So far, it doesn’t appear that that is the case.
Think about it. If it turned out that rapid climate change events are caused by comets, it would imply the climate system is far more stable than we thought, that abrupt climate change events are not part of the inherent variability of climate during glacial periods. That would perhaps allay fears that we could be pushing the system towards an abrupt climate change in the future. On the other hand, it would also suggest that cometary impacts are far far more common than we thought. Now that would be news. Perhaps further research by Kennett, Firestone and others will indeed show that to be the case. We’re not, however, holding our breath.
———-
*Not to mention that there is an event similar to the Younger Dryas at the end of at least one other glacial period, “termination III” (see e.g. Carlson et al., 2008).
Here is the NOAA Paleoclimatology Program page on Younger Dryas:
http://www.ncdc.noaa.gov/paleo/abrupt/data4.html
Excellant graphic.
Jim Cross (200) — I understand the warming and cooling quite well, thank you. Your second paragraph is quite a good summary, but there is no ‘cycle’ as is evidenced by the methane records for the two prior terminations as well as the details of termination 1; I suggest ‘oscillation’ as a more neutral term.
Your question is precisely what I set forth in comment #192, augmented by comment #191 and other prior comments, as the YDB hypothesis. It is based on a quite remarkable (near) simultaneous occurrance of events across North America and northern Europe. From the NOAA page linked above, it seems that greatly enhanced flow out the St. Lawrence may need to be added to the list of simultaneous events.
Anyway, please do read comments #191 and #192 again. That YDB augmented YD to some extent can hardly be doubted. The hypothesis is that YDB significantly augmented YD.
Correction to comment #199: 12.9 – 11.6 = 1300 years, almost as long as the enitre presumed period for DO cycling of 1500 years. In any event, the temperature in central Greenland continued to improve until the 8l2 ka CR event.
We are still at square one for evidence on an impact affecting any ice sheet or inducing any rapid drainage event. I have seen not one shred of field data supporting the idea. We still have lots of data recording the fluctuations of the ice sheets, the lake levels of the impounded proglacial lakes. Still no sign. You underestimate the amount of effort and research that has gone into reconstructing the behavior of the LIS and FIS, literally lifetimes of digging and mapping. Something catastrophic will leave evidence.
Something catastrophic will leave evidence.
It has, a black mat demarcation layer in the statigraphy, nanodiamonds, spherules, various shocked materials, crater fields, the quest for evidence has just begun. We are in the all out speculation phase of this result, as it should be. Already the Peruvian impact, Burckle crater and the Holocene impact working group have revolutionized our thinking, and this is just another line of evidence.
How much evidence do you think the Tunguska event would have left after 12,900 years? We’re lucky to get anything and the fact that we are still gleaning evidence after 12,900 years itself is evidence of the size of the thing, especially considering that most of that evidence was immediately involved, altered and removed by subsequent catastrophic flooding events shortly thereafter.
I for one am grateful for the heads up on these things.
mauri pelto (203) — The most immediate piece of field evidence might well be Charity Shoal Impact Crater, Lake Ontario. Substantiating this would require a better age determination (if possible) together with a better understanding of flow to Gulf of Saint Lawrence during YD.
I certainly have an appreciation of the field work required and a deep admiration for those who collect it. Indeed, all that work has collected the evidence of several (nearly) simultaneous events across North America and northern Europe.
Thomas Lee Elifritz (204) — Well stated!
On the matter of possible flow from Lak Agassiz at YD initiation,
the Fall 2008 AGU abstract
OS11A-1109
Characterizing the Discharge Features of Glacial Lake Agassiz during the Post-Marquette Period Using Marine Seismic-Reflection Methods
Gary, J L, Wattrus, N J, Colman, S M, Voytek, E B
demonstrates appropriate sediments in Lake Superior for a latter stage of Lake Agassiz drainage. A similar abstract from the Fall 2007 AGU meeting by the first three authors indicates an intent to do the work described above and then continue, further south, to look for similar features (if any) for the YD stage drainage. So by the next meeting we might actually have some decent data regarding the widely surmised, but unsupported, drainage to the east during YD.
The graph from NOAA found in the link in comment #201 and directly linked as
http://www.ncdc.noaa.gov/paleo/abrupt/images/data4-climate-changes-lg.gif
suggests a flow to the Gulf of St Lawrence of an astounding 0.15 Sv maintained for over 1300 years! I would certainly like to see the paper(s) supporting this graph, but just now have no good idea what search terms to use. In any case, I don’t see how Lake Agassiz, Lake Warren, etc. could maintain such a large and steady flow. More melting of eastern LIS than I had realized, I suppose.
Figure 6 in
G. Larson and R. Schaetzl
REVIEW: Origin and Evolution of the Great Lakes
J. Great Lakes Res. 27(4):518–546
Internat. Assoc. Great Lakes Res., 2001
indicates the extent of LIS at 13 ka, just before YD initiation. This tends to indicate a great difficulty with drainage of Lake Agassiz to the east, too much ice in the way. On the othr hand, it confirms that Lake Ontario was filled to overflowing with ice, helping to advance the idea that the Charity Shoal Impact was at YD onset and caused flow to the east to substantially increase.
The first several abstracts from the Fall 2005 AGU meeting support strong flows into the Gulf of St Lawrence at YD initiation althugh the first also suggests the alternate routing through the arctic. In any case, it seems there were substantial flows:
http://www.agu.org/meetings/fm05/fm05-sessions/fm05_PP12A.html
David,
Won’t a large discharge of freshwater accelerate the THC? Using simple hydrostatics: if you have two columns of water of equal depth next to each other and the one on the right has more freshwater, won’t the pressure at the bottom of the left column be higher than the one on the right? (p=h*rho*g) I’m trying to picture how all this freshwater flow is supposed to effect a diffusion (i.e., concentration) limited system that’s several thousand meters deep near the ocean floor.
Pt (207) — As I understand it from the paper linked earlier by SteveF and the Rahmstorf paper cited in comment #191, a sufficiently large freshwater flux (greater than 0.06 Sv) into the North Atlantic causes THC to switch to the ‘colder’ mode, that is, avoiding the Nordic Sea and so causing cooling in Greenland and northern Europe.
Pt, this may help
http://scholar.google.com/scholar?sourceid=Mozilla-search&q=fresh+water+saline+circulation
Usual advice; click “recent” and evaluate partly by number of citing articles that carry a paper’s ideas forward.
John A. Rayburn, Peter L. K. Knuepfer and David A. Franzi, “A series of large, Late Wisconsinan meltwater floods through the Champlain and Hudson Valleys, New York State, USA”, Quaternary Science Reviews, Volume 24, Issue 22, November 2005, Pages 2410-2419, show that flood events went further south, as in the title, during early Younger Dryas. There was no ice in Lake Ontario, so I suppose the dates in the review paper cited in comment #206 are radiocarbon dates. Sigh. This now suggests that the Charity Shoal Impact was long before YDB, but not necessarily. In any case, there was substantial flow into the North Atlantic from the proglacial lakes east of Lake Agassiz and the suthors state that this was much larger than any (presumed) Lake Agassiz addition.
Lev Tarasov & W.R. Peltier, “Arctic freshwater forcing of the Younger Dryas cold reversal”, Nature 435, 662-665 (2 June 2005)
http://www.nature.com/nature/journal/v435/n7042/full/nature03617.html
offer the unusual hypothesis that it was a substantial melt from Keewatin ice dome, writing “The underlying source of this strong discharge into the Arctic Ocean is the large Keewatin ice dome, whose existence at the Last Glacial Maximum was recently confirmed through analyses of space geodetic and absolute gravity constraints. The strength of local sourcing is evident in that even with the removal of all runs that have northwest drainage of Lake Agassiz at -12.8 kyr, ensemble discharge into the Arctic Ocean still dominates, with a 1sigma range of 1.1–1.5 dSv.” The authors also indicate a rather basic hydrological problem with massive dischanges from other sources (in the supplimental information), a problem fully in accordance with what is observed in earthquake-caused submarine turbidity currents: dirty water sinks.
In any case, this paper offers a different source for fresh water injection into the Nordic Sea, called in GIN sea in the paper.
Andrew G. Couch and Nick Eyles, “Sedimentary record of glacial Lake Mackenzie, Northwest Territories, Canada: Implications for Arctic freshwater forcing”, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 268, Issues 1-2, 10 October 2008, Pages 26-38, show that glacial Lake Mackenzie cleaned dirty meltwater so that the flow into the Arctic might have been clean enough to remain on the surface. The authors explain why their methods would not detect any large, sudden increases in flow. The dates of the study are about right for all of YD. The Turner et al. paper previously cited references a paper showing some decreased salinity at around the right time for YD. In any case, but not mentioned in these papers, rafted ice would still have the effect of forcing sea ice out Fram Strait into the Nordic Sea.
Similarly for rafted ice down the Hudson and later out to the Gulf of St Lawrence, irrespective of what portiion of the enhanced flow was dirty. (we’ll lump these together as the mid-Atlantic.)
For the Baltic Ice Lake (BIL), both outbursts only removed about 10 m of bedrock, from a study read long ago and my own brief observations of the flow channel. So first the smaller 5–15 m drop and then the final 25 m drop did not remove much of the rock; the water was quite clean. Much of it, together with rafted ice, then made its way into the Nordic Sea.
The conjectured explanation for the great intensity of YD is the combination of ice from the Arctic and meltwater/ice from Early BIL, together with whatever contribution the mid-Atlantic provided. That these events occurred nearly simultaneously, rather than spread over centuries, is taken to explain why YD at 1300 years was shorter than the less intense and longer (1900 years) similar interval in termination 3.
The increased fresh water flow into the Arctic during the pre-YD stage of deglaciation, from sources all around the Arctic, caused about 700 years of gradually declining temperatures in central Greenland just before the YD temperature plunge. This appears to be ever increasing volumes of sea ice pushed south out of Fram Strait, but not enough to significantly affect methane concentrations nor to cause a THC transition. I have not located any evidence of catastrophic flows to the Arctic down the MacKenzie River at any time near 12,900 calendar years ago.
From the Rayburn et al. paper cited in comment #210, “We estimate the steady-state meltwater discharge into the North Atlantic to be 0.3–0.6 Sv. The first flood event was a combined Iroquois/Vermont outflow at around 10,900 14C yr BP that released 700 km3 of meltwater into the North Atlantic through the Hudson Valley with an estimated discharge of 1.1 Sv. A second outflow event released 2500 km3 through the Hudson Valley shortly after the first event. Finally, approximately 1500 km3 was released to the North Atlantic through the Gulf of St. Lawrence at the incursion of the Champlain Sea about 150–300 years later.” we see that the mid-Atlantic region provided substantial flux beginning at about the right time. Previous comments noted the catastrophic release from the Early Baltic Ice Lake at about the same time as YD onset in central Greenland and the near simultaneous switching of proglacial Lake Agassiz drainage from the the south to another outlet. In my just prior comment, it is proposed that the extra freshwater fluxes from BIL and mid-Atlantic, together with rafted ice, were then enough to cause a THC transition to the “cold” regime, evidenced by the central Greenland sudden temperature drop.
The YDB hypothesis is that these nearly simultaneous terrestrial changes were started by the YDB encounter with one or more ET objects.
Jim Cross in comment #95 suggested the possiblity of considrable melt.
I used the impact calculator for a 15 km comet of the density of Shoemaker-Levy 9 to obtain “Energy before atmospheric entry: 5.88 x 10^23 Joules = 1.41 x 10^8 MegaTons TNT” and the target ice “melted or vaporized is 3680 km^3 = 883 miles^3”. That volume is comparable to the volumes of meltwater released from various glacial lakes at YD onset. This size is purely conjectural and there is no additional evidence, AFAIK, of suddenly increased fluxes. This paragraph is only to suggest the possiblity of catastrophically large increased melt triggering the three nearly simultaneous terrestrial events.
Well, there’s that.
So what’s in that layer of black stuff then?
I’ve seen a lot of poor to crappy science reporting, but that one takes the cake. I’m guess the paper cited doesn’t even mention the hypothesized extraterrestrial impact.
Re #193, Field’s paper doesn’t reproduce the artic nor antarctic Be-10 ice concentrations going back well beyond the YD. They do however generate a rule of thumb that says that 10% of Be-10 concentration change causes +/- 1 W/m2 change in radiative forcing due to 2XCO2, volacanoes (internal factors). If you look at the Be-10 concentration from antarctic going back from 30 kya-15 kya that’ll put the forcing at -60 W/m2, obviously not possible with internal factors. The artic Be-10 starts major deviation from the antartic around 30 kya and then converges back together about prior to the YD time period. If there was external (solar, geomagnetic field meander) forcing that initiated the YD cooling, it began at least 10 kya before the actual event.
[Response: You have it backwards. Changes in climate cause changes in 10Be in those experiments, not the other way around. – gavin]
David, Do you have a ref. that shows the path of the deep conveyor belt? There are millions of km3 of ocean water (ca. 35k ppm) to deal with, and a few thousand freshwater km3 seems like a drop in the bucket. Perhaps you/someone else can explain how the THC gets into a cold spell.
Not much in the way of detail here, but Sandy Harrison from the University of Bristol dumps some cold water over this. No continent wide forest firesto be found.
http://www.sciencedaily.com/releases/2009/01/090126173729.htm
If you believe that paper ‘disproves’ anything, you need to find a career outside of science. That headline in no way resembles the content of the cited paper, and the content of the cited paper doesn’t even address the hypothesized extraterrestrial impact. The fact that this kind of science reporting even occurs in the United States is a clear indication of how far the level of science education has fallen in the America of today.
219. You may be right. The story is rather sketchy and I have not got hold of the actual paper. But it SEEMS to be taken directly from the University of Bristol news release.
http://www.eurekalert.org/pub_releases/2009-01/uob-cit012609.php
Alright, now I do have the paper, but haven’t read the entire thing. From the intro:
We also test the hypothesis that
a comet impact initiated continental-scale wildfires at 12.9 ka; the
data do not support this idea, nor are continent-wide fires indicated at any time during deglaciation. There are, however, clear
links between large climate changes and fire activity. Biomass
burning gradually increased from the glacial to the beginning of
the Younger Dryas. Although there are changes in biomass burning
during the Younger Dryas, there is no systematic trend.
Pt (217) — Here is a link to a starter page on THC:
http://www.pik-potsdam.de/~stefan/thc_fact_sheet.html
Also see the Rahmstorf 1995 paper cited in a previous comment; its available from his publications page.
Regarding the supposed “continent-wide” fires, this seems rather irrelevant and also appears to contradict the ammonia data from NGISP. Another example of the difficulty of determining what actually happened at such a deep time.
bigcitylib (221) — Can you provide a link to the paper? I don’t seem to be able to locate it.
Looking at Stefan Rahmstorf’s THC fact sheet, I noticed that the Labrador Sea is important. I’ll now offer the suggestion that mid-Atlantic meltwater and rafted ice shut down the Larador Sea deepwater formation.
In any case, I think I misstated the situation in the Arctic. There is some evidence for increased freshwater in the Arctic at the time interval in question.
Ok, then it’s extremely poor science. How do you test a hypothesized pinpoint chronological impact event by looking at gradual changes over centuries and millennia?
In short, you don’t. If you want to refute (not disprove, since it hasn’t even been ‘proven’ yet, and science doesn’t ‘prove’ anything anyways) the impact hypothesis, which rests upon the observed impact crater fields, the strong statigraphic demarkation layer, and the observed particulate anomalies in the observed statigraphic layer, then you work on refuting any one of those lines of evidence, you don’t present some hazy result about increase wildfires associated with global warming.
This paper is a really great example of bad science.
When you google the paper title, it gives you this link :
http://www.ggy.bris.ac.uk/news/?NewsID=200901260001
Look at the graph. Nothing extraordinary there. No mention of the comet hypothesis, no glaring evidence of extreme events which could lay down such a dramatic layer of charcoal, nothing much there at all. What we have is someone using a controversy to publicize a science paper.
David and others interested. It was emailed to me by Cherry.lewis@bristol.ac.uk. Either email her directly or, failing that, email me at bigcitylib@hotmail.com
Re: 223.
Refute
Re*fute”\ (r?*F3t”), v. t. [imp. & p. p. Refuted; p. pr. & vb. n. Refuting.] [F. r[‘e]futer, L. refuteare to repel, refute. Cf. Confute, Refuse to deny.] To disprove and overthrow by argument, evidence, or countervailing proof; to prove to be false or erroneous; to confute; as, to refute arguments; to refute testimony; to refute opinions or theories; to refute a disputant.
There were so many witnesses in these two miracles that it is impossible to refute such multitudes. –Addison.
Syn: To confute; disprove. See Confute.
Webster’s Revised Unabridged Dictionary, © 1996, 1998 MICRA, Inc.
#214 Hank
This article
http://www.pnas.org/content/105/18/6520.full
that I referred to earlier, states this about the black mats:
“Of the 97 geoarchaeological sites of this study that bridge the Pleistocene-Holocene transition (last deglaciation), approximately two thirds have a black organic-rich layer or “black mat” in the form of mollic paleosols, aquolls, diatomites, or algal mats with radiocarbon ages suggesting they are stratigraphic manifestations of the Younger Dryas cooling episode 10,900 B.P. to 9,800 B.P. (radiocarbon years).”
Basically, this is saying that it is layer of decayed organic matter formed in wet soils. If correct, it has nothing to do with burning.
bigcitylib (224) — Thanks, but Thomas Lee Elifritz in comment #223 provided a link to a summary based on the paper. After reading the link, I largely agree with TOmas’s commentary.
David,
If you would prefer to base you opinion on the summary…
So you are citing the dictionary in your analysis of a scientific result. Ok. That will always get me going.
I have no problem with the result of the paper, which is intuitively – global warming, more wildfires. However, what I am questioning is linking this centennial and decadal result, spread over millennia, to a geologically instantaneous hypothesis, when it doesn’t address any of the lines of evidence which have been developed in support of that hypothesis. I am even more opposed to the press coverage of this result. This kind of thing happens all the time, each time for dramatic than the previous.
OBAMA REVEALED TO BE A SPACE ALIEN
See what I mean? I think it would be great if there never was a Clovis impact, and that perhaps the stressed Clovis population simply resorted to huge wildfires for hunting in some sort of post glacial feeding frenzy.
Is that the truth? Is the black mat simply the result of extensive ice sheet flooding, followed by extreme climate change, drought and wildfires? Why do the hypothesized crater fields still point to Lake Michigan? What about the nanodiamonds? What about the associated extraterrestrial particulate layer and the geological markers? All of the evidence I can gather about this press release is that it seems a public relations ploy.
Too late, the feeds have picked it up, it’s everywhere. This is going to be more fun sorting out than the PETM.
Meanwhile, science trudges on.
Re #216. Fields used GCMs along with modifications to solar forcing. The generated the 10% Be-10 => 1 W/m2 based on these simulations.
What’s critical to Be-10 deposition are sulfate ions in the upper troposphere. If you plot [SO4] along with the Be-10 concentrations, there’s a direct relationship between Be-10 & [SO4] for many thousand years prior to YD cooling, but not so for Greenland Be-10 which has an inverse relationship. The basic point here is that there a lead in over several thousand years (for example increased volcanic activity) that may have caused the YD cooling.
[Response: Which [SO4] record are you using to determine this? Be10 scavenging by aerosols doesn’t depend strongly on volcanic activity because there is always enough aerosol to pick up whatever Be10 is produced. The idea that volcanism thousands of years before caused the YD is rather dubious though. – gavin]
Re #222, David thanks. There’s positive and negative flows into/out of the NA. There’s an “equilibrium” point (at 0 Sv) that is critical in these studies (well mixed conditions are also assumed throughout — resistance due to water bouyancy may make this reasonable; which means the system may be more stable). Will get back to you on this later.
Re#230. See the [SO4] record in Taylor dome and GRIP. I believe sulphate in aerosols are required to precipitate out Be-10 from the upper troposphere. There’s increases [SO4] activity in both records over 1000s of years prior to YD cooling. If increased volcanic activity is not particularly palatable, then there’s dimethlysulphate from ocean dwelling algae (but I don’t see how SO4 could be puffed off that high into the atmosphere), or if that is not likely, then if we go by too much internal forcing (using the 10% rule from Field) means coincidence between external forcing (including geomagnetic field meander) and and incr. sulfate activity.
[Response: You are correlating [SO4] in Taylor Dome with 10Be in GRIP? I don’t see the connection (or the peer reviewed paper that shows this?). Why doesn’t it show up if you do the correlation with [SO4] at GRIP? And how do you know that both aren’t simply responding to the large climate changes that characterised the last ice age? Can we see some real work here…? – gavin]
Thomas Lee Elifritz (229) — Actually, I have some doubts about the conclusion that more warming implies more wildfires in North America during ther period studied. Foremost is that North America was inhabited by Paleoamericans at that deep time. There is direct evidence from later time that the hunter-gathers in North America intensionally set forest fires. See, for example, “Ancient Forests”. I have no evidence, one way or the other, about whether the Paleoamericans did the same or how significant such would be.
The other, more minor, objection is that it seems that much of the lower 48 suffered drought throughout (much of) YD. I didn’t bother to keep a link to the paper seems it seems remote from the primary purpose of this thread. The relevance here is that this would tend to help explain the flat slope of the graph during YD; no temperatures required.
All in all, and having looked at other limnological studies with some care, it seems the paper in question implies essentially nothing regarding YDB.
In retrospect now I can see why the paleofire group would want to hitch their star to the holocene impact group. The misreporting of it can only increase exposure of this remarkable and relevant problem to the drunken masses.
Having not read the paper, I don’t know what sort of proxies they are using to develop their correlations, but they seem insufficiently resolved to detect brief intense widespread impact induced fires or even if that would be the largest relevant forcing issues on what was to come.
Re #232. As [SO4]_Taylor Dome (Antartica) goes up starting around 30 kya, the [Be-10]_Taylor Dome goes up until about the YD period. [SO4]_GRIP goes up starting around 30 kya, the [Be-10] goes down. The [Be-10] signature in Taylor Dome and GRIP diverge around 30 kya. [SO4] in both places going up suggests global [SO4] activity (most probably volcanic since [SO4] must get to the upper troposphere to bring down Be-10. The question you ask is why there’s an inverse relationship between [SO4] and [Be-10] in GRIP. One possible explanation is that the earth’s magnetic field in the north deflected the energetic [Be-10] from Greenland; the poles of the earth can meander independent of each other.
I don’t understand your last question.
The last part should say “energetic protons.”
Having just reviewed some of the basics of this remarkable problem of the Quaternary – Pleistocene – Holocene extinctions, I noticed that someone might want to update this excellent wiki page with relevant Holocene ET impact hypotheses pros and cons.
http://en.wikipedia.org/wiki/Quaternary_extinction_event
Sea level is always a good climate indicator, and I noticed a graph somewhere outlining sea levels during the previous interglacial, where two sharp reversals are shown, much more dramatic than the Younger Dryas. Plus that interglacial was warmer, and fairly abrupt as well.
Not sure of the proxies they use, but here is a paper where I was only tangentially logistically involved in :
http://geology.geoscienceworld.org/cgi/content/abstract/24/9/775
There are some nice links at the bottom of the page. It’s seems to me we are in the same situation as the Clovis.
Humans, playing with fire, overhunting, changing the landscape, climate changing, ice sheets melting, and the occasional large impact, on the order of hundreds to thousands to tens of thousands of years. Now speed that up the modern world, as in geologically instantaneous. Or even worse, a really bad day. I’m sure glad we’ve got NOAA and NASA to protect us.
Clovis culture must have been spectacular.
Thomas Lee Elifritz (227) — If you find the link to a paper on sea level reversals during termination 2, kindly post it. Such reversals would seem to disagree with the methane record analyzed in Carlson et al., 2008, linked in the footnote to Eric’s orginal essay beginning this thread. I, at least, see no easy way to reconcile such evidence.
http://geology.geoscienceworld.org/cgi/content/abstract/34/10/817
http://adsabs.harvard.edu/abs/2002AGUFMPP72B..12A
Impacts are going to be different, but there appears to be some nontrivial oceanic climate energy coupling between hemispheres during reversals and oscillations.
That might explain some of the discrepancies.
I don’t think they are invoking an impact theory to explain the Younger Dryas. Rather, the Younger Dryas simply lends concomitant evidence of an impact theory supported by many legs.
Gavin, is “Pt” known to you as someone who could show some real work, as you ask, to support any of the various notions “Pt” is posting?
Or are you being polite? I can’t tell if these posts are just throwing words out and saying maybe there’s some explanation hidden in them.
The impact is invoked to help explain the ‘extinctions’ because other lines of evidence have various problems.
If you throw an unusual impact into the mix, then all of the conflicting evidence starts to make sense. Any one of them is sufficient to cause the megafauna extinctions given enough time – man, climate and impacts. The problem is the abruptness and the regional nature of the events.
The question still remains – what really happened. The farther back you go, the harder those questions get. What is remarkable about this situation, is that nothing much has changed in the intervening 12,900 years, except now we’re doing it again on a much larger scale. One big impact and all of your problems will be instantly reorganized into a scramble for survival. That’s how unprepared the human race is for the inevitable.
The funny thing is, it doesn’t need to be this way. We could easily prepare ourselves for anything thrown at us if only we were to quit breeding uncontrollably, and even that’s a relatively (i.e. easy) simple problem to solve.
Hank, H2O2 can be created by an oxygen radical from the ozone cycle via: H2O + 1/2 O2(.) = H2O2. The reaction typically requires Fe(III)-ligand intermediate, supplied by dust particles. So the H2O2 signal from melting can be amplified by the “dust” reaction.
Looking at the H2O2 in the ice record from the arctic(which goes back 14.5 kya – 8 kya) — and interpreting it in terms of the dust contribution, there are weak 400 year cycles prior to the YD onset, nothing during the YD period, followed by a rapid increase within a few decades (ice melting in the NA), a gradual increase after that, followed by a strong up slope starting circa 9.5 – 10kya. The 400 cycles might be due to ITCZ movement which may have led to the wet conditions in the Sahara during YD cooling. The slope increase (ca. 9.5-10 kya) is probably due to the onset of extreme dry conditions in the Sahara which has been attributed to orbital tilt and perihelion timing.
There’s bound to be a coupling between events in the tropics/semi-tropics and the rapid cooling in the NA at YD onset: no heat pump (via moisture transport) from the tropics (as alternate to THC?).
Hey, Pt, you may be the world’s expert on this stuff, but without citations to published work I — or likely any other amateur reader here — can’t tell if you’re just throwing words on the page, or riffing from your last paper in Nature or Science. Got sources for any of that?
ReCaptcha says:
“fanatics NOTED”
Hank, Chill. If you want to read peer reviewed, read the journals. This is a blog for crying out loud. I’m not selling anything. Take it for what it’s worth.
For those of you interested in bolide and impact physics and statistics, the analysis of these has moved to Mars :
http://hirise.lpl.arizona.edu/ESP_011618_1885
The atmosphere is very thin, but the dust covering makes finding these things very easy.
Of course, we’ve also seen what happens at Jupiter :
http://en.wikipedia.org/wiki/Comet_Shoemaker-Levy_9
The moon is an ideal experimental testing ground with no atmosphere at all, but the noise level is very high ”
http://en.wikipedia.org/wiki/Transient_lunar_phenomenon
Captcha : net problem
And to complete the connection between humans playing with fire and climate, we have these reports out of Australia :
http://news.bbc.co.uk/2/hi/asia-pacific/7878106.stm
A possible Younger Dryas Laurentide ice sheet impact remnant feature transposed onto glacial runoff terrain near Lake Nipigon :
Nipigon Feature
What I see here is a typical large butterfly feature with a smaller vaguely oval feature along the northwest edge, and lots of catastrophic flooding.
A butterly? I do not see the real find here, looks like fools gold still. I encourage you to revisit the field reports from Tom Lowell, that comment on the lack of an outlet in this particular locale.
http://www.eeescience.utoledo.edu/Faculty/Fisher/Lake%20Agassiz%20Research.htm
I’ve read all those papers, mostly Peter Barnett. I don’t object to the general analysis that most of the Nipigon events postdate the Younger Dryas event, I just thought if there was a big bolide impact on the ice sheet at 12,900 BP in that area, traveling Northwest to Southeast, then perhaps there might be some evidence of it, and thus I decided to look. That is the only thing that stands out.
The ‘butterfly’ is a result of Tunguska simulations. Most of the traditional Nipigon flows were east and west of Nipigon, and certainly there were many flows after any presumed Younger Dryas flow. Sea level rise is nearly continuous during the entire deglaciation, there are no obvious reversals. We already know that the YD outflows were not especially remarkable, there has to be something else, and this is yet another example of ‘something’. Of course, it could be nothing.
And it was so much fun looking, and rewarding to spot something.