Ice sheet melt identified as trigger of Big Freeze

Mar 31, 2010

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, 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 .

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 .

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 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 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 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.

The study will help shed light on the implications of fresh water input into the North Atlantic today. There are current concerns that changes in the salinity of the ocean today, could cause another shut down of the . Current climate changes, including global warming, may be altering the planetary system which regulates evaporation and precipitation, and moves fresh water around the globe.

The findings, which show the cause, location, timing and magnitude of the mega-flood, will enable scientists to better understand how sensitive both oceans and climates are to fresh-water inputs and the potential climate changes which may ensue if the North Atlantic continues to alter.

Dr Mark Bateman, from the University of Sheffield's Centre for International Drylands Research at the Department of Geography, said: "The findings of this paper through the combination of luminescence dating, landscape elevation models and sedimentary evidence allows an insight into what must have been one of the most catastrophic geological events in recent earth's history. They also show how events within the Earth-climate system in North America had huge impacts in Europe."

Explore further: Experts express concern over cyclone trends in the British-Irish Isles

More information: The paper, entitled ‘Identification of Younger Dryas outburst flood path from Lake Agassiz to the Arctic Ocean’ was published in Volume 464 (7289) of Nature: Julian B. Murton, Mark D. Bateman, Scott R. Dallimore, James T. Teller and Zhirong Yang.

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2.7 / 5 (3) Mar 31, 2010
This does not bode well for global warming fans such as myself.
3 / 5 (2) Mar 31, 2010
This does not bode well for global warming fans such as myself.


By why would you be a fan of global warming..
3 / 5 (6) Mar 31, 2010
In this instance, global(?) warming melted an ice sheet which led to localized cooling in Europe.
4.5 / 5 (11) Mar 31, 2010
Fans or Sceptics we're all in the same boat so to speak and 1400 years of consequences is a long time to pay if we sleepwalk into making a mess of our planets climatic balance. Every study like this goes a little way to understanding the complexity of it all.
2.8 / 5 (12) Mar 31, 2010
In my opinion, this demonstrates the variability of earths climate which is and always will be out of our control. seems like the earth has a natural system for regulating temps over thousands of years. Go figure! Global warming is happening, but probably not as much due to humans as the alarmists suggest. I wonder if we will decide to start spending tax payer money on warming the planet when the global cooling scenario starts. It will be continued redisribution of wealth either way.
2.3 / 5 (9) Mar 31, 2010
@fhtmguy: You didn't read the article or you didn't understand it. Which one is true?
1.3 / 5 (7) Mar 31, 2010
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Abstract: Using Google Earth and browsing the geographic appearance of the Earth’s crust starting from the South Pacific Ocean right above Antarctica and traveling over to Drake’s Passage and into the South Atlantic Ocean there seems to be a visual trace that some sort of cosmic collision occurred in that area. The impact of the object surfed across the ocean and collided with the bottom of South America where it once connected to Antarctica creating Drake’s Passage opening. This impact also may have had the kinetic energy to break the Earth’s crustal plate and create the fault lines in addition to changing Earth’s axial tilt. [Report and Opinion. 2010;2(2):1-2]. (ISSN: 1553-9873).

3 / 5 (8) Mar 31, 2010
3.3 / 5 (8) Mar 31, 2010
This isn't exactly a new theory, nor is evidence that a mega-flood occurred just before the onset of the Younger Dryas.
3.1 / 5 (7) Mar 31, 2010
In this instance, global(?) warming melted an ice sheet which led to localized cooling in Europe.

The Younger Dryas was not a local event. The entire northern hemisphere was affected and the last glaciation (not Ice Age, btw, but glaciation), while it had been ending, lasted another 1000 years.
4.5 / 5 (6) Mar 31, 2010
This event is very interesting but it has limited use in predicting the effects of the current global warming. The freshwater deposited in the north Atlantic by this flood were several orders of magnitude bigger than freshwater melt-off from Greenland today.
2.7 / 5 (7) Apr 01, 2010
@fhtmguy: You didn't read the article or you didn't understand it. Which one is true?

I understood his point and drew the same conclusion from the article. A very rapid release of fresh water caused a warming climate to plunge back into a Glaciation period that lasted centuries. Perhaps you need to think about what happened and why before you start accusing people of being lazy and or ignorant.
5 / 5 (6) Apr 01, 2010
This megaflood came from water dammed up by receding glaciers that covered North America.
There is no such possibilty now because there are no such glaciers. They left and behind them we have the Great Lakes.
4.5 / 5 (2) Apr 01, 2010
Uh-oh. So should I invest in air-conditioning or electric blankets? :)
3 / 5 (2) Apr 01, 2010
I had several "wa-h-aat?" moments reading this article. a) the Canadian northern artic islands extend right up to very nearly the north pole. How does added freshwater ice from the Mckenzie delta get round to the Atlantic gulf stream during an ice age? b) the continental height of land between Artic and Atlantic / Gulf of Mexico is very low, about 450 meters just south of the great lakes. The plains at province of Alberta, just south of McKenzie delta, are at elevation of about 1000 meters. Why wouldn't Lake A. have drained directly to the Atlantic via St. Lawrence, rather than out through McKenzie?

Of course none of this reduces our need to study and mitigate potential global warming.
2.5 / 5 (4) Apr 01, 2010
Global warming is good because it always has been. Warm periods = boom times; Cooling periods = contraction, starvation, disease. Take your pick.

The predictions of current Gulf Stream change are being disproven with every new measurement. It ain't happening. The mega-flood was remarkable because it was so mega. Quantity matters.
3 / 5 (6) Apr 01, 2010
@jeffhans: Shootist put it well. This has absolutely no bearing on the climate variations we see today or will see within a large number of generations. By attempting to equalize what is seen today with what has happened in massive events in the past would be ridiculous and would indicate that that person had no clue what this article actually said.

And yet you agreed with fhtguy. Good jorb.
2.5 / 5 (4) Apr 01, 2010
b) the continental height of land between Artic and Atlantic / Gulf of Mexico is very low, about 450 meters just south of the great lakes. The plains at province of Alberta, just south of McKenzie delta, are at elevation of about 1000 meters. Why wouldn't Lake A. have drained directly to the Atlantic via St. Lawrence, rather than out through McKenzie?

Of course none of this reduces our need to study and mitigate potential global warming.

Remember that "sea level" has changed. Not just from addition or removal of water but from the land rebounding after the ice sheet melted. Land south of the Great Lakes that is now 450 meters above sea level may have been 100 meters below sea level when a 2km thick ice sheet lay atop it.

But the mega flood did exit the St. Lawrence, and through Hudson Bay and down, what would become, the Mississippi.
2.7 / 5 (3) Apr 01, 2010
Why wouldn't Lake A. have drained directly to the Atlantic via St. Lawrence, rather than out through McKenzie?"

These pathways are still visible on topographic maps of the area. Hell you can see the drainage pattern in Google Earth.

Maybe I am misunderstanding what you're saying.
3 / 5 (2) Apr 02, 2010
Yeah this really doesn't have much to do with current weather and climate variation. The mechanisms are a great thing to study but I doubt we're going to be increasing the ocean's volume by 10% as that flood did. The sea level rise from that singular event is estimated at 2 to 10 meters almost instantly.
3 / 5 (4) Apr 04, 2010
Where do you get that +10 percent figure? That there is a LOT of water. Are you including the successive Spokane Floods, which also happened in the late, even very late Pleistocene?

Also- it's not entirely a sure thing at what specific temp/salinity the conveyor will break down, nor is it entirely certain just how much meltwater is and will be contributed by the Greenland icesheet- especially if warming continues. Probably isn't entirely wise to sound the "stand down" just yet.
3 / 5 (2) Apr 04, 2010
2.3 / 5 (3) Apr 04, 2010
brianH as you posted on 01/04 i'm assuming that was a joke right? "that global warming is good"
well, apart from events like the great die off 250 million years ago yeah.
we're finding more an more how complex the mechanisms of the climate system are, your not too aware of the effects on our crop yields from the changing climate, or the range shift being experianced by countless species.
this idea put about that CO2 is a boom for bio-growth is basically true but misses a lot in it's broad generalisations just as making generalisations about climate change are.
3 / 5 (4) Apr 04, 2010
A nice summary, but I don't see that figure anywhere in it.
Also, I notice that there is no mention of glacial flood outlet to arctic via the MacKenzie, nor any mention of Spokane floods, which were apparently the most massive of all of these Laurentide Ice Sheet glacial floods.
The article appears to be a little incomplete/dated. That's alright though- this flood event through the Mackenzie still dumped hundreds of cubic kilometers of meltwater into the arctic ocean, and obviously would have had significant effects, regardless of whether it interfered with the conveyor.
5 / 5 (1) Apr 06, 2010
Volume of ice reduction over thermal expansion of water equation yields the total volume, divide by present total volume and you get your percentage.

The laurentide Ice sheet flooding total figures for the 9000 year event were well over 10% total ocean volume.

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