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The Start of the Younger Dryas

Glitch

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According to ice-core sample taken from Greenland, we reached the peak of the last glacial period sometime between 23,000 and 25,000 years ago. Beginning around 15,000 years ago the Holocene Interglacial period began and everything began to start warming up. When it was suddenly interrupted by a very sudden drop in temperature of between an 8°C and 10°C at 12,900 years ago. That sudden drop in temperature marks the beginning of the Younger Dryas. That drop in temperature kept the planet between 8°C and 10°C colder than it would have been for ~1,200 years. Finally, at around 11,700 years ago the Younger Dryas ended and the Holocene Interglacial period continued.

What I want to discuss is our understanding of what caused that sudden drop in temperature that started the Younger Dryas.

There are two prevailing theories:
  1. Lake Agassiz, a massive lake the size of Canada's Manitoba Province fed by glacial run-off, was blocked from flowing down the Mississippi River, and exited the St. Lawrence River instead. All that freshwater entering the Atlantic Ocean shutdown the Gulf of Mexico current (a.k.a. the Atlantic Conveyor) that supplies the Atlantic with its warmth.
  2. The second theory is much more straight forward: An extraterrestrial event (either an asteroid or comet) broke up and struck the Laurentide Ice Sheet over North America.
Shutting down the Atlantic Conveyor would drop temperatures in the northern hemisphere by between 8°C and 10°C on average. So that fits our temperature observations in Greenland's ice-core samples. The problem that this theory has is that it cannot explain the sudden disappearance of all the mega-fauna during the Younger Dryas. Mastodons, Woolly Mammoth, Sabre-toothed cats, Dire Wolves, and dozens more species of mega-fauna suddenly vanished between 12,900 and 10,000 years ago. These species were alive and kicking ~24,000 years ago, during the peak of the last glacial period when temperatures were also between 8°C and 10°C colder. They also survived countless other glacial and interglacial periods during the last 2.58 million years that this ice-age has been occurring. What was so special about the Younger Dryas that it could cause the extinction of so many mega-fauna all around the world?

The second theory would seem to explain both the sudden drop in temperature, and the disappearance of the mega-fauna. There is also some evidence to support this theory, like the Carolina Bay's they have located in both North and South Carolina, Florida, Georgia, Maryland, and New York, as well as in Nebraska.

LiDAR image of Carolina Bays 20 miles (32 km) southwest of Fayetteville, NC

It has been suggested that these elliptical bays were created when an asteroid or comet impacted the Laurentide Ice Sheet and caused large chunks of ice to reach sub-orbital speeds and be deposited as far south as Florida. The angle of these bays all orientate around northern Michigan. Even the bays in Nebraska are pointing in that direction, and that is where the theory begins to have problems.


Bays in Nebraska are degraded by erosion and deposition (Lat. 40.566, Lon. -98.123, elevation 545 meters)

Lake Agassiz was at the southern most part of the Laurentide Ice Sheet. The lake had four exits, the Mississippi, St. Lawrence, and MacKenzie Rivers, as well as Hudson Bay. Which means that there was no ice sheet to impact in Michigan. It had already retreated further north by the time Lake Agassiz existed. The only way to get those kind of elliptical bays is by impacting an ice sheet and flinging huge chunks of ice sub-orbitally. So the impact would have had to be during a time when the Laurentide Ice Sheet also covered Michigan, before the formation of Lake Agassiz. Which would make the impact older than 15,000 years, sometime during the last glacial period. But if the impact was older than 12,900 years, what killed the mega-fauna?

It is possible that they got the size of Lake Agassiz wrong, and the Laurentide Ice Sheet actually extended into Michigan at that time. However, this would mean blocking the St. Lawrence River, and only allowing Lake Agassiz to exit via the Mississippi, MacKenzie, and Hudson Bay.

It is also possible that both theories could be true. An impact on Laurentide Ice Sheet could have caused Lake Agassiz to suddenly release it waters into both the Atlantic and Pacific. Which would explain the Missoula and Spokane Mega Floods.

What do you think happened that could explain both the sudden drop in temperature and the extinction of the mega-fauna around the world during that same period?
 
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While researching this topic I came across this image someone made using Google Earth that lines up the orientation of all the known Carolina Bays. It would appear that there are two impact sites that caused these bays, one in Michigan, and the other in Wisconsin. This would also seem to demonstrate that the asteroid or comet did indeed break apart before impacting Earth.


Lake Agassiz was also located much further north, above the Great Lakes, where the Laurentide Ice Sheet was also located. In other words, there was no glacial ice to impact in either Wisconsin or Michigan 12,900 years ago.
 
Cordelier said:
The Carolina Bays don't strike me as having an impact origin. I think they were created by a gentler process, like a Thermokarst. They're probably relics of the Wisconsin glaciation.
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Thermokarsts are created by permafrost when it melts, it creates a depression. Thermokarsts do not create either the perfect elliptical bays or the raised edges that are distinct with Carolina Bays, and they do not all point in the same direction or overlap. There was also no permafrost in Florida, the Carolinas or Georgia during the last glacial period, where the Carlonia Bays are located, so they could not be thermokarsts.


An example of thermokarsts in Alaska
 
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Christopher Swezey of the US Geographical Survey disagrees with you.

https://www.researchgate.net/public...ns_of_the_Atlantic_Coastal_Plain_Province_USA

From Pages labelled 47 of the PDF (emphasis mine):

"Theories of origin related to meteorite impacts (e.g., Melton and Schriever 1933; MacCarthy 1937; Prouty 1952) may be ruled out because the OSL [Optically stimulated luminescence] ages show a wide range of values and because there is no evidence of disturbance of the underlying strata. Likewise, theories of origin related to traditional karst phenomena (e.g., Smith 1931) may be ruled out because of the absence of limestone beneath most Carolina Bays."

From Pages labelled 48-49:

"The OSL ages indicate that the Carolina Bays formed during approximately the same time interval as the eolian dunes and sand sheets in the river valleys and in the Carolina Sandhills region. In other words, the Carolina Bays are relict features that formed when air temperatures were cooler, wind velocities were greater, and vegetation density was reduced. Very similar oriented lakes are present today in many high-latitude regions such as Alaska (Fig. 2.15), Canada, Russia, and the Falkland Islands (e.g., Rex 1961; Carson and Hussey 1962; Coté and Burn 2002; Wilson et al. 2002; Hinkel et al. 2005, 2012; Arp et al. 2011; Karlsson et al. 2012; Morgenstern et al. 2013; Zhan et al. 2014). These high-latitude oriented lakes are thermokarst lakes that developed as a result of thaw and collapse of frozen ground, with subsequent modification by lacustrine and (or) eolian processes. Most studies of thermokarst lakes have been conducted in the continuous permafrost zone of northern Alaska, but thermokarst lakes are also present in zones of discontinuous permafrost such as the boreal forest regions of central Alaska and northern Quebec (Jorgenson et al. 2012; Coulombe et al. 2016). In the Barrow region of northern Alaska, the dominant wind direction is from the east to northeast, and this wind generates gyres that promote erosion of the north and south shores of the thermokarst lakes, leading to the elongate orientation of the lakes (Zhan et al. 2014). In other words, the orientation of thermokarst lakes is governed by patterns of wind-driven circulation and longshore drift, whereby sediment accumulates on the downwind (lee) side of the lakes and the lakes expand by erosion in zones that are oriented 50° to the wave approach or approximately perpendicular to the dominant wind direction (Rex 1961; Carson and Hussey 1962; Zhan et al. 2014). Many of these thermokarst lakes in northern Alaska have modified an older, stabilized substrate of eolian sand (Carter 1981)."
 

When did the massive eruption in Yellowstone take place ?

This could have caused a massive cooling.
 
He is also making assumptions not based on evidence. He acknowledges that the southern limit of permafrost during the last glacial maximum was located in central or northern Virginia, citing French et al. 2009 and French and
Miller 2014. Then goes on to make the erroneous assumption that since the boreal forest extended as far south as the Carolinas then so must the permafrost. Boreal forests exists where there is no permafrost, so his assumption is not based upon anything.

He also acknowledges taking samples from the Carolina Bay ridges, but fails to explain how those ridges could have been created since thermokarsts do not form ridges. None of the thermokarsts in Alaska, Canada, or Siberia have ridges. Nor do thermokarsts overlap, which the Carolina Bays do. He also claims - based entirely on the range of the boreal forest at the time - that the permafrost extended as far south as Georgia, but fails to explain how the Carolina Bays in Florida or Nebraska could have existed if they were thermokarsts.

There is also additional evidence of an extraterrestrial event 12,900 years ago. The shocked quartz, micro-diamonds, higher levels of iridium, and other indicators all point to an extraterrestrial event over North America 12,900 years ago. Some of this evidence is coming from the Channel Islands off the coast of California, and could not possibly have anything do to with permafrost.

Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling - The Proceedings of the National Academy of Sciences, Volume 104, Issue 41, pp. 16016-16021, October 2007

The evidence that an extraterrestrial impact occurred 12,900 years ago seems pretty conclusively. But that still presents the problem with the fact that the Laurentide Ice Sheet had already receded north of both Wisconsin and Michigan by 12,900 years ago. There was no glacial ice to impact. So where is the crater, or craters if it was multiple impacts? Since the underlying strata of the Carolina Bays was not disturbed, they could not have been created from the rocky debris created from an impact. Only large chunks of ice, which would have left no residual debris after melting, could have created those bays.
 
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noonereal said:
When did the massive eruption in Yellowstone take place ?

This could have caused a massive cooling.
Click to expand...
The last large eruption from Yellowstone was 640,000 years ago. Before that it erupted 1.3 million and 2.1 million years ago respectively, and it would certainly have an effect on the climate. The last eruption from a super volcano occurred 74,000 years ago from the Toba super volcano in Sumatra, and it almost wiped out the human species according to our DNA.

It should be noted that the mega-fauna survived both the Toba and Yellowstone eruptions.
 
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Discontinuous permafrost can co-exist with boreal forests. From the text I quoted earlier:

"thermokarst lakes are also present in zones of discontinuous permafrost such as the boreal forest regions of central Alaska and northern Quebec"

And what do you mean he doesn't explain how the ridges could have formed? Did you look at the title of the paper? They're Eolian Dunes created by the prevailing winds.

I'll read the paper you cited when I get a chance, but just because there may have been a meteor strike doesn't mean it was responsible for the Carolina Bays. As Swezey points out, there is no evidence of disturbance of the underlying strata of the Carolina Bays. Even if there were a strike on the Laurentide ice sheet, it seems to me that any ice chunks would have been vaporized either from the impact or from the air resistance of travelling through the atmosphere at supersonic speeds. And even if they weren't vaporized, they certainly would have caused a disturbance in the underlying strata of wherever they impacted.
 
Glitch said:
What do you think happened that could explain both the sudden drop in temperature and the extinction of the mega-fauna around the world during that same period?
Click to expand...
Two different explanations: The Lake Agassiz event is most likely what caused the Younger Dryas temperature drop.

The extinction of the megafauna (especially in the Americas) was probably mostly caused by humans settling new areas for the first time, which were unpopulated or sparsely populated prior to this. The early Native American tribes began populating and spreading throughout the New World around this time (I know they got there earlier than this, but the populations were very small). Humans had also moved into parts of Europe and Russia that were previously too cold for human life during the brief warm period preceding the Younger Dryas. This resulted in lots of megafauna which had previously not encountered humans being hunted to extinction.
 
Cordelier said:
Discontinuous permafrost can co-exist with boreal forests. From the text I quoted earlier:
Click to expand...
Very true, and boreal forests can exist without permafrost. One is not an indicator of the other.

Cordelier said:
"thermokarst lakes are also present in zones of discontinuous permafrost such as the boreal forest regions of central Alaska and northern Quebec"
Click to expand...
That is not entirely true. Thermokarsts exist where permafrost once existed, but has either completely melted or is in the process of melting. If there was never any permafrost, then there cannot be a thermokarst.

Cordelier said:
And what do you mean he doesn't explain how the ridges could have formed? Did you look at the title of the paper? They're Eolian Dunes created by the prevailing winds.
Click to expand...
Prevailing winds do not form perfect elliptical shapes. Winds create dunes in the form of waves, not geometric shapes. So that part of his paper is complete bullshit. You will never find an example of winds creating elliptical patterns anywhere.

As I already pointed out above, the fact that the underlying strata was not disturbed indicates that it had to be ice that made those Carolina Bays. Ice would have left no traces once it melted, which would have happened quickly after traveling Mach 11 to reenter the atmosphere.

It also means that the Laurentide Ice Sheet had to extend as far south as central Wisconsin and Michigan by 12,900 years ago, otherwise the impactor would have struck land and not ice. This poses a problem, since everything I have seen of that time period indicates that the Laurentide Ice Sheet had already receded back into Canada and was no longer present in either Wisconsin or Michigan.

Since the impact point is immutable, determined by the angle of the Carolina Bays, and none of the underlying strata of the Carolina Bays were disturbed, the impact could only have occurred when the ice sheet extended into both States. Which would put the date at 15,000 years ago or before. Unless we somehow got the location of the Laurentide Ice Sheet wrong for that time.
 
There were not enough humans on the planet to make a dent in the mega-fauna population. Furthermore, humans had been living in North American, Europe, and Australia for 30,000+ years, with the mega-fauna, before the mega-fauna went extinct. So they could not have been hunted into extinction. Various human species and mega-fauna had co-existed for hundreds of thousands of years before they went extinct. Nor was cold a factor, since the mega-fauna had already survived much colder temperatures for a much longer period during prior glacial events.

It should also be noted that according to our own DNA, whatever killed the mega-fauna 12,900 years ago, also severely depleted the human population. Not as badly as the Toba eruption 74,000 years ago, but it was a noticeable decline.
 
This is the best information that I've found concerning the location of the Laurentide Ice Sheet from 18,000 years ago until 5,000 years ago. The data comes from the Geological Survey of Canada:

Since we know the impacts that created the Carolina Bays occurred in central Wisconsin and Michigan, and the impacts had to be on ice and not on land, that would place the impacts prior to ~13,500 years ago. Which means that it could not be the event that started the Younger Dryas or wiped out the mega-fauna.
 
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