Academic Bun Fight: the Pleistocene/Holocene Boundary and the Younger Dryas Impact Hypothesis

Bayesian chronological analyses consistent with synchronous age of 12,835–12,735 Cal B.P. for Younger Dryas boundary on four continents

Authors:

Kennett et al

Abstract:

The Younger Dryas impact hypothesis posits that a cosmic impact across much of the Northern Hemisphere deposited the Younger Dryas boundary (YDB) layer, containing peak abundances in a variable assemblage of proxies, including magnetic and glassy impact-related spherules, high-temperature minerals and melt glass, nanodiamonds, carbon spherules, aciniform carbon, platinum, and osmium. Bayesian chronological modeling was applied to 354 dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled YDB age range for this event of 12,835–12,735 Cal B.P. at 95% probability. This range overlaps that of a peak in extraterrestrial platinum in the Greenland Ice Sheet and of the earliest age of the Younger Dryas climate episode in six proxy records, suggesting a causal connection between the YDB impact event and the Younger Dryas. Two statistical tests indicate that both modeled and unmodeled ages in the 30 records are consistent with synchronous deposition of the YDB layer within the limits of dating uncertainty (∼100 y). The widespread distribution of the YDB layer suggests that it may serve as a datum layer.

That was really bad science

Problematic dating of claimed Younger Dryas boundary impact proxies

Author:

Holliday

Extract:

The PNAS paper by Kennett et al. (1) uses statistical methods in an attempt to improve the geochronological control for purported Younger Dryas boundary (YDB) impact proxies. The underpinning data for these analyses are problematic, however, as discussed by Meltzer et al. (2) and Holliday et al. (3). Several examples illustrate the problems. At Barber Creek the YDB zone is at ∼100 cm below the surface, but in situ wood charcoal dated to 10,500 ± 50 14C y B.P. (∼12.5 k cal yrs) is documented below 100 cm (3). The large SD for the modeled age of the YDB here (1) (12,865 ± 535 cal yrs) easily accommodates the high-precision date on the charcoal from below the spherule zone. At Blackville the sediments dated by optically stimulated luminescence are mixed and thus the dates cannot be considered reliable (3). The supposed impact proxies at Bull Creek are from 307- to 312-cm depth (3). The radiocarbon date of ∼12,960 cal yrs is from 298 to 307 cm and is a bulk sample on soil organic matter, thus representing a mean residence time for the soil carbon. Impact proxies are, therefore, older than ∼12,960 y by some unknown amount; they are also found in abundance in strata less than 3,000 y old. The Usselo soil in northwest Europe spans ∼1,400 y based on ∼50 radiocarbon ages, dating primarily to the Allerød and into the YD (2).

Thbbbbbppppt:

Reply to Holliday and Boslough et al.: Synchroneity of widespread Bayesian-modeled ages supports Younger Dryas impact hypothesis

Authors:

Kennett et al

Extract:

Holliday (1) rejects age-depth models for the Younger Dryas boundary layer (YDB) in Kennett et al. (2), claiming that they are incorrect for several reasons, including age reversals, high age uncertainties, and use of optically stimulated luminescence (OSL) dating. These same claims previously were presented in Meltzer et al. (3) and were discussed and refuted in Kennett et al. (2). These criticisms apply to nearly all dated archaeological and geological sequences, including the Odessa meteorite impact crater, where paradoxically, Holliday et al. (4) modeled an impact age using OSL dating (greater than 70% of dates used) with large uncertainties (to greater than 6,000 y) and age reversals (greatre than 40% of dates are reversals). Thus, Holliday (1) argues against a practice that he and many other researchers have used and continue to use today. In an ideal world, all dates would be in perfect chronological order with high accuracy and certainty, but such scenarios are rarely possible (2). It is because of such dating difficulties that Bayesian analysis is a powerful chronological tool, and is rapidly becoming the archaeological standard.

Europe Suddenly Became Much Drier 13,000 Years ago

Molecular-based moisture indicators, remains of midges and climate simulations have provided climate scientists with the final piece to one of the most enduring puzzles of the last Ice Age.

For years, researchers have struggled to reconcile climate models of the Earth, 13,000 years ago, with the prevailing theory that a catastrophic freshwater flood from the melting North American ice sheets plunged the planet into a sudden and final cold snap, just before entering the present warm interglacial.

Now, an international team of scientists, led by Swedish researchers from Stockholm University and in partnership with UK researchers from the Natural History Museum (NHM) London, and Plymouth University, has found evidence in the sediments of an ancient Swedish lake that it was the melting of the Scandinavian ice sheet that provides the missing link to what occurred at the end of the last Ice Age. The study, published in Nature Communications, today, examined moisture and temperature records for the region and compared these with climate model simulations.

Francesco Muschitiello, a PhD researcher at Stockholm University and lead author of the study, said: "Moisture-sensitive molecules extracted from the lake's sediments show that climate conditions in Northern Europe became much drier around 13,000 years ago."

link.

Siliceous Scoria Droplets are NOT Evidence of a Younger Dryas Impact Since They are Anthropogenic in Origin

Anthropogenic origin of siliceous scoria droplets from Pleistocene and Holocene archaeological sites in northern Syria

Authors:

Thy et al

Abstract:

Siliceous scoria droplets, measuring from 1 to 10 mm, from one late Pleistocene and four early Holocene archaeological sites in northern Syria are compared to similar droplets previously suggested to be the result of a cosmic impact at the onset of the Younger Dryas global cooling event. The findings demonstrate that the presence of siliceous scoria droplets are independent of age and thus are not specific to the beginning of the Younger Dryas. Occurrences have not been reported from natural deposits, but are instead associated with buildings destroyed by fire and thus appear to be restricted to archaeological sites. We therefore conclude that melting of building earth in ancient settlements can occur during fires reaching modest temperatures. There is no evidence to suggest that siliceous scoria droplets result from very high temperature melting of soil and are the result of a cosmic event.

Nanodiamond-Rich Layer across Three Continents at the Younger Dryas Boundary

Nanodiamond-Rich Layer across Three Continents Consistent with Major Cosmic Impact at 12,800 Cal BP

Authors:

Kinzie et al

Abstract:

A major cosmic-impact event has been proposed at the onset of the Younger Dryas (YD) cooling episode at ≈12,800 ± 150 years before present, forming the YD Boundary (YDB) layer, distributed over greater than 50 million km2 on four continents. In 24 dated stratigraphic sections in 10 countries of the Northern Hemisphere, the YDB layer contains a clearly defined abundance peak in nanodiamonds (NDs), a major cosmic-impact proxy. Observed ND polytypes include cubic diamonds, lonsdaleite-like crystals, and diamond-like carbon nanoparticles, called n-diamond and i-carbon. The ND abundances in bulk YDB sediments ranged up to ≈500 ppb (mean: 200 ppb) and that in carbon spherules up to ≈3700 ppb (mean: ≈750 ppb); 138 of 205 sediment samples (67%) contained no detectable NDs. Isotopic evidence indicates that YDB NDs were produced from terrestrial carbon, as with other impact diamonds, and were not derived from the impactor itself. The YDB layer is also marked by abundance peaks in other impact-related proxies, including cosmic-impact spherules, carbon spherules (some containing NDs), iridium, osmium, platinum, charcoal, aciniform carbon (soot), and high-temperature melt-glass. This contribution reviews the debate about the presence, abundance, and origin of the concentration peak in YDB NDs. We describe an updated protocol for the extraction and concentration of NDs from sediment, carbon spherules, and ice, and we describe the basis for identification and classification of YDB ND polytypes, using nine analytical approaches. The large body of evidence now obtained about YDB NDs is strongly consistent with an origin by cosmic impact at ≈12,800 cal BP and is inconsistent with formation of YDB NDs by natural terrestrial processes, including wildfires, anthropogenesis, and/or influx of cosmic dust.

Younger Dryas Pleistocene Quaternary Greenland Paleotemperature Mystery Solved

A new study of three ice cores from Greenland documents the warming of the large ice sheet at the end of the last ice age – resolving a long-standing paradox over when that warming occurred.

Large ice sheets covered North America and northern Europe some 20,000 years ago during the coldest part of the ice age, when global average temperatures were about four degrees Celsius (or seven degrees Fahrenheit) colder than during pre-industrial times. And then changes in the Earth's orbit around the sun increased the solar energy reaching Greenland. Beginning some 18,000 years ago, release of carbon from the deep ocean led to a graduate rise in atmospheric carbon dioxide (CO2).

Yet past analysis of ice cores from Greenland did not show any warming response as would be expected from an increase in CO2 and solar energy flux, the researchers note.

In this new study, funded by the National Science Foundation and published this week in the journal Science, scientists reconstructed air temperatures by examining ratios of nitrogen isotopes in air trapped within the ice instead of isotopes in the ice itself, which had been used in past studies.

Not only did the new analysis detect significant warming in response to increasing atmospheric CO2, it documents a warming trend at a rate closely matching what climate change models predict should have happened as the Earth shifted out of its ice age, according to lead author Christo Buizert, a postdoctoral researcher at Oregon State University and lead author on the Science article.

link.

Stone Tools From Younger Dryas Pleistocene Belgium

A sealed flint knapping site from the Younger Dryas in the Scheldt valley (Belgium): Bridging the gap in human occupation at the Pleistocene–Holocene transition in W Europe

Authors:

Crombé et al

Abstract:

Based on the evidence of a recently excavated, sealed site, situated at Ruien “Rosalinde” in the Belgian Scheldt valley, the response of hunter-gatherers to changing climate at the transition from the temperate Allerød to the cold Younger Dryas is discussed. Radiocarbon dated to the end of the Allerød or the very beginning of the Younger Dryas, the site of Ruien provides the earliest evidence of a refined lithic technology characterized by the use of a soft stone hammer and the production of straight and regular blade(let)s from intensively prepared cores with two opposite platforms and sharp striking angles. In the course of the Younger Dryas and Early Pre-boreal this knapping method will become standard all over Europe, from the Tanged Point Technocomplex in the North to the (Epi)Laborian in the South. It contrasts sharply with the knapping style of previous lithic traditions, such as the late Federmesser/Azilian and Bromme Technocomplexes, which was much less elaborated and mainly oriented towards the knapping of short irregular blades with a hard stone hammer. This apparently abrupt technological change was also accompanied by increased raw material procurement networks, extending over up to 250 km, and a marked microlithisation of the hunting equipment. Finally, the site of Ruien is also important as it demonstrates the limited archaeological visibility of Younger Dryas sites, explaining the scarcity of such sites within western Europe.

26 of 29 Sites Cited for "Supporting" Younger Dryas Impact are NOT From the Younger Dryas

Most supposed impact indicators at 29 sites are too old or too young to be remnants of an ancient comet that proponents claim sparked climate change at the end of the Ice Age, killed America's earliest people and caused a mass animal extinction

Controversy over what sparked the Younger Dryas, a brief return to near glacial conditions at the end of the Ice Age, includes a theory that it was caused by a comet hitting the Earth.

As proof, proponents point to sediments containing deposits they believe could result only from a cosmic impact.

Now a new study disproves that theory, said archaeologist David Meltzer, Southern Methodist University, Dallas. Meltzer is lead author on the study and an expert in the Clovis culture, the peoples who lived in North America at the end of the Ice Age.

Meltzer's research team found that nearly all sediment layers purported to be from the Ice Age at 29 sites in North America and on three other continents are actually either much younger or much older.

Scientists agree that the brief episode at the end of the Ice Age — officially known as the Younger Dryas for a flower that flourished at that time — sparked widespread cooling of the Earth 12,800 years ago and that this cool period lasted for 1,000 years. But theories about the cause of this abrupt climate change are numerous. They range from changes in ocean circulation patterns caused by glacial meltwater entering the ocean to the cosmic-impact theory.

The cosmic-impact theory is said to be supported by the presence of geological indicators that are extraterrestrial in origin. However a review of the dating of the sediments at the 29 sites reported to have such indicators proves the cosmic-impact theory false, said Meltzer.

Meltzer and his co-authors found that only three of 29 sites commonly referenced to support the cosmic-impact theory actually date to the window of time for the Ice Age.

The findings, "Chronological evidence fails to support claim of an isochronous widespread layer of cosmic impact indicators dated to 12,800 years ago," were reported May 12, 2014, in the Proceedings of the National Academy of Sciences.

link.

Bull Creek Nanodiamond Spike Does NOT Support the Younger Dryas Impact Hypothesis

Quantifying the distribution of nanodiamonds in pre-Younger Dryas to recent age deposits along Bull Creek, Oklahoma Panhandle, USA

Authors:

Bement et al

Abstract:

High levels of nanodiamonds (nds) have been used to support the transformative hypothesis that an extraterrestrial (ET) event (comet explosion) triggered Younger Dryas changes in temperature, flora and fauna assemblages, and human adaptations [Firestone RB, et al. (2007) Proc Natl Acad Sci USA 104(41):16016–16021]. We evaluate this hypothesis by establishing the distribution of nds within the Bull Creek drainage of the Beaver River basin in the Oklahoma panhandle. The earlier report of an abundance spike of nds in the Bull Creek I Younger Dryas boundary soil is confirmed, although no pure cubic diamonds were identified. The lack of hexagonal nds suggests Bull Creek I is not near any impact site. Potential hexagonal nds at Bull Creek were found to be more consistent with graphene/graphane. An additional nd spike is found in deposits of late Holocene through the modern age, indicating nds are not unique to the Younger Dryas boundary. Nd distributions do not correlate with depositional environment, pedogenesis, climate perturbations, periods of surface stability, or cultural activity.

More Academic Bun Fight: The Younger Dryas Impact Argument Continues (And Starts Getting...Sharp)

Younger Dryas impact model confuses comet facts, defies airburst physics

Authors:

Boslough et al

Excerpt:

In PNAS, Wittke et al. (1) present evidence that they indicate supports major airbursts and/or impacts at the beginning of the Younger Dryas, as proposed by Firestone et al. (2). One of the major criticisms of the hypothesis has been the lack of any physics-based model for the hypothesized event (3). Wittke et al. (1) attempt to remedy this flaw by including a section entitled “Preliminary Impact Model.” Their model diverges significantly from the original but still provides no physics based argument and demonstrates a misunderstanding of comets, as well as the physics of airbursts.

Counterargument:

Reply to Boslough et al.: Decades of comet research counter their claims

Authors:

Napier et al

Excerpt:

Boslough et al. (1) offer no alternate explanation for ∼10 million tonnes of Younger Dryas spherules recovered from 18 sites across ∼50 million square kilometers of North America, Europe, and the Middle East (2). In addition, the authors claim that our hypothesis “demonstrates a misunderstanding of comets.” However, the misunderstanding is theirs alone, because the model they criticize is their own creation and not the one we adopt, which derives from a substantial body of comet literature (e.g., ref. 3).

And its getting personal...

Academic Bun Fight: Chobot Lake (Canada) Evdience for a Younger Dryas Impact?

Reply to Ives and Froese: Regarding the impact-related Younger Dryas boundary layer at Chobot site, Alberta, Canada

Authors:

James H. Wittke, Ted E. Bunch, Kenneth B. Tankersley, I. Randolph Daniel, Jr., Johan B. Kloosterman, Gunther Kletetschka, Allen West, and Richard B. Firestone

Excerpt:

Ives and Froese (1) challenge the identification of the Chobot black mat layer at the Younger Dryas (YD) boundary (YDB), claiming that no black mats have been documented in western Canada (2). To the contrary, Haynes, a lead investigator of YD-age black mats, mapped two YD-age mat sites in western Canada (figure 1 in ref. 3): one ∼200 km south of the Chobot site at Vermillion Lakes in Alberta (12,719 ± 156 cal BP) and another at the Niske site in Saskatchewan (12,748 ± 020 cal BP).

Furthermore, Ives and Froese (1) claim the Chobot black mat is simply an organic layer of “surface leaf litter and humic materials” with no evidence for a “black algal mat.” We do not claim that the mat is algal in origin (2), nor is that a requirement. Haynes (3) describes YD black mats as being “dark gray to black because of increased organic carbon (0.05–8%)” and that sometimes, the mats are algal, but, often, the mats are simply enriched in charcoal, humates, diatomite, and other organics. Nonalgal black mats are present at Folsom, NM (3); Arlington Canyon, CA (2, 3); Sheriden Cave, OH (2); Lommel, Belgium (2); and Abu Hureyra, Syria (2); as well as at the Chobot site (2).

and in reply...

The Chobot site (Alberta, Canada) cannot provide evidence of a cosmic impact 12,800 y ago

Authors:

John W. Ives and Duane Froese

Excerpt:

Continued reference in the paper by Wittke et al. (1) to the Chobot site regarding an impact occurring at the Younger Dryas boundary (YDB) concerns scientists familiar with this region. The authors claim that no radiometric dating at the site is possible but have previously reported ages that are not consistent with their interpretation. They also claim that abundant Clovis points are present to justify the age of the site and associated impact spherules.

Chobot and other sites surrounding Buck Lake have been investigated by professional archaeologists within the provisions of the Historical Resources Act of Alberta. The Chobot site is thinly stratified: artifact bearing deposits are within 50 cm of the surface. Critically, the Chobot collection contains a record of the entire Holocene cultural sequence, with rare Early Prehistoric and more common Middle and Late Prehistoric diagnostic projectile points. Spatial analytical approaches can be applied to disentangle such records to a degree but require rigorous analysis of provenience data, a measure not applied at this site. The statement by Wittke et al. (1) that there are abundant Clovis points is not accurate: The fluted point they illustrate is one of three known from the site (2). Similarly, the assertion that there are “tens of thousands of Clovis-age flakes and tools” (1) is unsubstantiated. Because the great majority of diagnostics postdate the Clovis era, most accompanying artifacts are undoubtedly from later time intervals too (e.g., ref. 3). Charlie Lake Cave has provided the only radiometric dates for fluted points in western Canada (4). There, fluted points postdate the YDB; this could also be true of the Chobot fluted points.

Academic Bun Fight: Was There or Was There NOT an Impact at the Beginning of the Younger Dryas?

No:

Wittke et al. (1) present evidence of a major cosmic impact at the onset of the Younger Dryas (YD) episode, including some markers found in the top of the well-known Usselo marker horizon (UH). This finding is contrary to our extensive radiocarbon dating effort from this horizon (2), which shows that the UH at Aalsterhut postdates the onset of the YD. Furthermore, Wittke et al. (1) misinterpret the origin of the UH: this horizon is a well-defined paleosoil that formed during the Allerød and the early YD in the top part of coversand. This coversand was deposited before the Allerød, during cold and dry conditions, and is part of the European Sandbelt. Wildfires were common and occurred throughout this period, rather than synchronously with the onset of the YD (3).

Yes!

Van Hoesel et al. (1) refer to nanodiamonds at the top of the Usselo horizon at Aalsterhut, The Netherlands, having an average age of 10.845 ± 0.015 14C ka (12.70 ± 0.06 cal ka) (1); they found no nanodiamonds outside hat layer. Earlier, nanodiamonds were reported at the top of theUsselo in Lommel, Belgium,∼30 km southwest of Aalsterhut, acknowledged as the Younger Dryas boundary layer (YDB) [Tian et al. (2)]; those researchers also found no nanodiamonds outside that layer.

It all comes down to dating.

Darmouth Group Finds Evidence of Younger Dryas Impact

The impact occurred about 12,900 years ago, at the beginning of the Younger Dryas period, and marks an abrupt global change to a colder, dryer climate with far-reaching effects on both animals and humans. In North America, the big animals all vanished, including mastodons, camels, giant ground sloths and saber-toothed cats. Their human hunters, known to archaeologists as the Clovis people, set aside their heavy-duty spears and turned to a hunter-gatherer subsistence diet of roots, berries and smaller game.

It is not disputed that these powerful environmental changes occurred, but there has long been controversy over their cause. The classic view of the Younger Dryas cooling interlude has been that an ice dam in the North American ice sheet ruptured, releasing a massive quantity of freshwater into the Atlantic Ocean. The sudden influx is thought to have shut down the ocean currents that move tropical water northward, resulting in the cold, dry climate of the Younger Dryas.

But Sharma and his co-authors have discovered conclusive evidence linking an extraterrestrial impact with this environmental transformation. The report focuses on spherules, or droplets of solidified molten rock expelled by the impact of a comet or meteor. The spherules in question were recovered from Younger Dryas boundary layers at sites in Pennsylvania and New Jersey, the layers having been deposited at the beginning of the period. The geochemistry and mineralogy profiles of the spherules are identical to rock found in southern Quebec, where Sharma and his colleagues argue the impact took place.

link.

Interhemisphere Climate Forcing During the Younger Dryas

Northern Hemisphere forcing of Southern Hemisphere climate during the last deglaciation

Authors:

1. Feng He (a)
2. Jeremy D. Shakun (b)
3. Peter U. Clark (c)
4. Anders E. Carlson (a,c,d)
5. Zhengyu Liu (a,e)
6. Bette L. Otto-Bliesner (f)
7. John E. Kutzbach (a)

Affiliations:

a. Center for Climatic Research, Nelson Institute for Environmental Studies, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA

b. Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA

c. College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA

d. Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA

e. Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA

f. Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, Colorado 80307, USA

Abstract:

According to the Milankovitch theory, changes in summer insolation in the high-latitude Northern Hemisphere caused glacial cycles through their impact on ice-sheet mass balance. Statistical analyses of long climate records supported this theory, but they also posed a substantial challenge by showing that changes in Southern Hemisphere climate were in phase with or led those in the north. Although an orbitally forced Northern Hemisphere signal may have been transmitted to the Southern Hemisphere, insolation forcing can also directly influence local Southern Hemisphere climate, potentially intensified by sea-ice feedback, suggesting that the hemispheres may have responded independently to different aspects of orbital forcing. Signal processing of climate records cannot distinguish between these conditions, however, because the proposed insolation forcings share essentially identical variability. Here we use transient simulations with a coupled atmosphere–ocean general circulation model to identify the impacts of forcing from changes in orbits, atmospheric CO2 concentration, ice sheets and the Atlantic meridional overturning circulation (AMOC) on hemispheric temperatures during the first half of the last deglaciation (22–14.3 kyr bp). Although based on a single model, our transient simulation with only orbital changes supports the Milankovitch theory in showing that the last deglaciation was initiated by rising insolation during spring and summer in the mid-latitude to high-latitude Northern Hemisphere and by terrestrial snow–albedo feedback. The simulation with all forcings best reproduces the timing and magnitude of surface temperature evolution in the Southern Hemisphere in deglacial proxy records. AMOC changes associated with an orbitally induced retreat of Northern Hemisphere ice sheets is the most plausible explanation for the early Southern Hemisphere deglacial warming and its lead over Northern Hemisphere temperature; the ensuing rise in atmospheric CO2 concentration provided the critical feedback on global deglaciation.

Draining of Lake Agassiz Caused Younger Dryas Snap Freezing

Caption: A new model of flood waters from melting of the Laurentide Ice Sheet and large glacial lakes along its edge that covered much of North America from the Arctic south to New England over 13,000 years ago, shows the meltwater flowed northwest into the Arctic first. This weakened deep ocean circulation and led to Earth’s last major cold period. A new model of flood waters from melting of the Laurentide Ice Sheet and large glacial lakes along its edge that covered much of North America from the Arctic south to New England over 13,000 years ago, shows the meltwater flowed northwest into the Arctic first. This weakened deep ocean circulation and led to Earth’s last major cold period.

For more than 30 years, climate scientists have debated whether flood waters from melting of the enormous Laurentide Ice Sheet, which ushered in the last major cold episode on Earth about 12,900 years ago, flowed northwest into the Arctic first, or east via the Gulf of St. Lawrence, to weaken ocean thermohaline circulation and have a frigid effect on global climate.

Now University of Massachusetts Amherst geoscientist Alan Condron, with Peter Winsor at the University of Alaska, using new, high-resolution global ocean circulation models, report the first conclusive evidence that this flood must have flowed north into the Arctic first down the Mackenzie River valley. They also show that if it had flowed east into the St. Lawrence River valley, Earth's climate would have remained relatively unchanged.

"This episode was the last time the Earth underwent a major cooling, so understanding exactly what caused it is very important for understanding how our modern-day climate might change in the future," says Condron of UMass Amherst's Climate System Research Center. Findings appear in the current issue of Proceedings of the National Academy of Sciences.

Events leading up to the sharp climate-cooling period known as the Younger Dryas, or more familiarly as the "Big Freeze," unfolded after glacial Lake Agassiz, at the southern edge of the Laurentide ice sheet covering Hudson Bay and much of the Canadian Arctic, catastrophically broke through an ice dam and rapidly dumped thousands of cubic kilometers of fresh water into the ocean.

This massive influx of frigid fresh water injected over the surface of the ocean is assumed to have halted the sinking of very dense, saltier, colder water in the North Atlantic that drives the large-scale ocean circulation, the thermohaline circulation, that transports heat to Europe and North America. The weakening of this circulation caused by the flood resulted in the dramatic cooling of North America and Europe.

Using their high resolution, global, ocean-ice circulation model that is 10 to 20 times more powerful than previously attainable, Condron and Winsor compared how meltwater from the two different drainage outlets was delivered to the sinking regions in the North Atlantic. They found the original hypothesis proposed in 1989 by Wally Broecker of Columbia University suggesting that Lake Aggasiz drained into the North Atlantic down the St. Lawrence River would have weakened the thermohaline circulation by less than 15 percent.

Condron and Winsor say this level of weakening is unlikely to have accounted for the 1,000-year cold climate event that followed the meltwater flood. Meltwater from the St. Lawrence River actually ends up almost 1,900 miles (3,000 km) south of the deep water formation regions, too far south to have any significant impact on the sinking of surface waters, which explains why the impact on the thermohaline circulation is so minor.

By contrast, Condron and Winsor's model shows that when the meltwater first drains into the Arctic Ocean, narrow coastal boundary currents can efficiently deliver it to the deep water formation regions of the sub-polar north Atlantic, weakening the thermohaline circulation by more than 30 percent. They conclude that this scenario, showing meltwater discharged first into the Arctic rather than down the St. Lawrence valley, is "more likely to have triggered the Younger Dryas cooling."

Condron and Windor's model runs on one of the world's top supercomputers at the National Energy Research Science Computing Center in Berkeley, Calif. The authors say, "With this higher resolution modeling, our ability to capture narrow ocean currents dramatically improves our understanding of where the fresh water may be going."

People ask me what we run on our dayjob supercomputers. Well. There ya go.

Younger Dryas Impactor Hypothesis Crashes and Burns

It seemed like such an elegant answer to an age-old mystery: the disappearance of what are arguably North America’s first people. A speeding comet nearly 13,000 years ago was the culprit, the theory goes, spraying ice and rocks across the continent, killing the Clovis people and the mammoths they fed on, and plunging the region into a deep chill. The idea so captivated the public that three movies describing the catastrophe were produced.

But now, four years after the purportedly supportive evidence was reported, a host of scientific authorities systematically have made the case that the comet theory is “bogus.” Researchers from multiple scientific fields are calling the theory one of the most misguided ideas in the history of modern archaeology, which begs for an independent review so an accurate record is reflected in the literature.

“It is an impossible scenario,” says Mark Boslough, a physicist at Sandia Laboratory in Albuquerque, N.M., where he taps the world’s fastest computers for nuclear bomb experiments to study such impacts. His computations show the debris from such a comet couldn’t cover the proposed impact field. In March, a “requiem” for the theory even was published by a group that included leading specialists from archaeology to botany.

Yet, the scientists who described the alleged impact in a hallowed U.S. scientific journal refuse to consider the critics’ evidence — insisting they are correct, even though no one can replicate their work: the hallmark of credibility in the scientific world.

[...]

A new look at the comet claim suggests all of these phenomena may be in play, apparently creating a peculiar bond of desperation as the theory came under increasing attack. Indeed, the team’s established scientists are so wedded to the theory they have opted to ignore the fact their colleague “Allen West” isn’t exactly who he says he is.

West is Allen Whitt — who, in 2002, was fined by California and convicted for masquerading as a state-licensed geologist when he charged small-town officials fat fees for water studies. After completing probation in 2003 in San Bernardino County, he began work on the comet theory, legally adopting his new name in 2006 as he promoted it in a popular book. Only when questioned by this reporter last year did his co-authors learn his original identity and legal history. Since then, they have not disclosed it to the scientific community.

West’s history — and new concerns about study results he was integrally involved in — raise intriguing questions about the veracity of the comet claim. His background is likely to create more doubts about the theory. And the controversy — because it involves the politically sensitive issue of a climate shift — is potentially more broadly damaging, authorities suggest.

[...]

West has no formal appointment at an academic institution. He has said he obtained a doctorate from a Bible college, but he won’t describe it further. Firestone said West has told him he has no scientific doctorate but is self-taught. West’s Arizona attorney refers to him in writing as: “A retired geophysicist who has had a long and distinguished career.”

In the early 1990s, a new-age business West was involved in Sedona, Ariz., failed, and his well-drilling company went bankrupt. Then he ran afoul of California law in small Mojave Desert towns in a scheme with two other men, with court records saying they collected fees up to $39,500 for questionable groundwater reports.

He originally was charged with two felonies for falsely representing himself as a state-licensed geologist but agreed to a no contest plea to a single misdemeanor of false advertising as part of plea bargain in which state records say he was fined $4,500. Two other men in the scam also were sanctioned.

Acknowledging he made a mistake, West has sought to downplay the 9-year-old conviction. And last September, after his impact theory colleagues learned of it, he went back to court in Victorville, Calif., convincing a judge to void the old plea.

After earlier denying any impropriety with his Younger Dryas work, West declined a recent interview request. Last month, he wrote a letter charging it was “highly prejudicial and distorted” to bring up his legal past in the context of his current studies. He is a member of “a group of two dozen dedicated scientists performing cutting-edge, although controversial, research,” he wrote.

...

ouch.

Homo confisio strikes again? Or ought that be Homo audacia?

More Questions Raised Over Younger Dryas Impact

Some scientists have thought that the Earth's Ice Age conditions 12,900 years ago were triggered by a meteor or comet. But a recent study suggests that the evidence pointing to the ancient impact is nothing more than fungus and other matter.

According to the impact theory, the event could have caused the extinction of North American mammoths and other species, and killed the early human hunters that occupied North America at the time. Yet the new study concludes that sediment samples taken as evidence of the impact are nothing more than common fossilized balls of fungus and fecal matter - not exactly signs of a space rock crashing into Earth.

Further, the samples -- spherules of carbon used by impact proponents to justify a meteor -- appear thousands of years before and after the Ice Age in sediment records, suggesting they have nothing to do with the impact, scientists said in a statement.

"People get very excited about the idea of a major impact causing a catastrophic fire and the abrupt climate change in that period, but there just isn't the evidence to support it," said lead researcher Andrew C. Scott at the University of London in the UK.

Still, proponents of an impact theory are not backing down.

According to theory, a comet impact or airburst in the atmosphere produced an enormous fire that raged from California to Europe. Melting volumes of ice in the North American ice sheet, the fire sent cold water surging into the world's oceans and knocked off balance the circulation of currents responsible for global heat transport.

Known as the Younger Dryas period or "Big Freeze," the 1,300 years of glacial conditions that followed is well documented in ocean cores and ancient soil samples.

Organic matter normal, not melted

Collected from the same locations in California and Arizona used by proponents of the meteor theory, sediment cores dating back to the inception of the cooling era were compared to samples of modern soil that had been subjected to wildfires. They were also largely identified as compact balls and tendrils of fungal matter known as sclerotia, which are produced by fungi naturally during challenging conditions—hardly unique byproducts of an impact-ignited fire.

Neither the charcoal nor the fossilized balls had been exposed to heat above 450 degrees Celsius (842 F), researchers said in a statement. Further, radiocarbon dating of the spherules, which were sampled from many layers of the sediment cores, found that their ages ranged from 16,821 to 11,467 years old: too wide a berth to count as meaningful trigger for the Younger Dryas period.

Experimental charring tests have shown that this organic matter was subjected to, at most, regular low intensity fire, researcher Nicholas Pinter of Southern Illinois University told SPACE.com. Also, such globules would have been destroyed in any mega fire described by impact proponents, Pinter added.

"After the carbon spherules, only one credible piece of supporting evidence remains -- the so-called nanodiamonds purportedly found in 12,900-year-old deposits," Pinter said. "Impact proponents are putting all of their remaining eggs in the nanodiamond basket."

hmmm. Nanodiamonds? hmmm.

NorAm Paleoindian Population Took Younger Dryas in Step

Paleoindian groups* occupied North America throughout the Younger Dryas interval, which saw a rapid return to glacial conditions approximately 11,000 years ago. Until now, it has been assumed that cooling temperatures and their impact on communities posed significant adaptive challenges to those groups. David Meltzer from the Southern Methodist University in Dallas, USA, and Vance Holliday from the University of Arizona in Tucson, USA, suggest otherwise in their review of climatic and environmental records from this time period in continental North America, published in Springer's Journal of World Prehistory.

From their analysis, they conclude that on the Great Plains and in the Rocky Mountains, conditions were in reality less extreme and therefore may not have measurably added to the challenge routinely faced by Paleoindian groups, who during this interval, successfully dispersed across the diverse habitats of Late Glacial North America.

Meltzer and Holliday question whether the impact of cooling on Pleistocene North Americans was actually that pronounced or widespread and, if it was, whether it was similarly abrupt and severe, and in the same direction, across North America. Their comprehensive review of the climate and environment of North America during that time and its possible impact suggests that the Young Dryas age cooling was not as sudden, extensive, or severe as has previously been suggested and the notion that these conditions may have taken the Paleoindians by surprise is questionable.

The authors conclude: "All things considered, it is likely that across most of North America, south of the retreating ice sheets, Paleoindians were not constantly scrambling to keep up with Younger Dryas age climate changes. After all, adapting to changing climatic and environmental conditions was nothing new to them – it was what they did."

no time...

Lake Agassiz Megaflood Caused Younger Dryas?

The main cause of a rapid global cooling period, known as the Big Freeze or Younger Dryas - which occurred nearly 13,000 years ago - has been identified thanks to the help of an academic at the University of Sheffield.

A new paper, which is published in Nature today (1 April 2010), has identified a mega-flood path across North America which channelled melt-water from a giant ice sheet into the oceans and triggering the Younger Dryas cold snap.

The research team, which included Dr Mark Bateman from the University of Sheffield's Department of Geography, discovered that a mega-flood, caused by the melting of the Laurentide ice sheet, which covered much of North America, was routed up into Canada and into the Arctic Ocean.

This resulted in huge amounts of fresh water mixing with the salt water of the Arctic Ocean. As a result, more sea-ice was created which flowed into the North Atlantic, causing the northward continuation of the Gulf Stream to shut down.

Without the heat being brought across the Atlantic by the Gulf Stream, temperatures in Europe plunged from similar to what they are today, back to glacial temperatures with average winter temperatures of -25oC. This cooling event has become known as the Younger Dryas period with cold conditions lasting about 1400 years. The cold of the Younger Dryas affected many places across the continent, including Yorkshire in the Vale of York and North Lincolnshire which became arctic deserts with sand dunes and no vegetation.

Before now, scientists have speculated that the mega-flood was the main cause of the abrupt cooling period, but the path of the flood waters has long been debated and no convincing evidence had been found establishing a route from the ice-sheet to the North Atlantic.

The research team studied a large number of cliff sections along the Mackenzie Delta and examined the sediments within them. They found that many of the cliff sections showed evidence of sediment erosion. This evidence spanned over a large region at many altitudes, which could only be explained by a mega-flood from the over-spilling of Lake Agassiz, which was at times bigger than the UK, at the front of the Laurentide Ice-sheet rather than a normal flood of the river.

Dr Bateman, who has been researching past environmental changes both in the UK and elsewhere in the world for almost 20 years, runs the luminescence dating lab at Sheffield. The lab was able to take the MacKenzie Delta sediment samples from above and below the mega-flood deposits, and find out when the mega-flood occurred, enabling its occurrence to be attributed to the start of the Younger Dryas.

no time, but it fits, in my mind at least, for the base cause of the Younger Dryas better than comet impact hypothesis.