Skip to comments.The Intriguing Problem Of The Younger Dryas—What Does It Mean And What Caused It?
Posted on 06/21/2012 10:11:38 AM PDT by Ernest_at_the_Beach
This is a follow up posting to Younger Dryas -The Rest of the Story!
Guest post by Don J. Easterbrook
Dept. of Geology, Western Washington University.
The Younger Dryas was a period of rapid cooling in the late Pleistocene 12,800 to 11,500 calendar years ago. It followed closely on the heels of a dramatically abrupt warming that brought the last Ice Age to a close (17,500 calendar years ago), lasted for about 1,300 years, then ended as abruptly as it started. The cause of these remarkably sudden climate changes has puzzled geologists and climatologists for decades and despite much effort to find the answer, can still only be considered enigmatic.
The Younger Dryas interruption of the global warming that resulted in the abrupt, wholesale melting of the huge late Pleistocene ice sheets was first discovered in European pollen studies about 75 years ago. Terrestrial plants and pollen indicate that arboreal forests were replaced by tundra vegetation during a cool climate. This cool period was named after the pale yellow flower Dryas octopetella, an arctic wildflower typical of cold, open, Arctic environments. The Younger Dryas return to a cold, glacial climate was first considered to be a regional event restricted to Europe, but later studies have shown that it was a world-wide event. The problem became even more complicated when oxygen isotope data from ice cores in Antarctica and Greenland showed not only the Younger Dryas cooling, but several other shorter cooling/warming events, now known as Dansgaard-Oerscher events.
The Younger Dryas is the longest and coldest of several very abrupt climatic changes that took place near the end of the late Pleistocene. Among these abrupt changes in climate were: (1) sudden global warming 14,500 years ago (Fig. 1) that sent the immense Pleistocene ice sheets into rapid retreat, (2) several episodes of climatic warming and cooling between ~14,400 and 12,800 years ago, (3) sudden cooling 12,800 years ago at the beginning of the Younger Dryas, and (4) ~11,500 years ago, abrupt climatic warming of up to 10º C in just a few decades. Perhaps the most precise record of late Pleistocene climate changes is found in the ice core stratigraphy of the Greenland Ice Sheet Project (GISP) and the Greenland Ice Core Project (GRIP). The GRIP ice core is especially important because the ages of the ice at various levels in the core has been determined by the counting down of annual layers in the ice, giving a very accurate chronolgoy, and climatic fluctuations have been determined by measurement of oxygen isotope ratios. Isotope data from the GISP2 Greenland ice core suggests that Greenland was more than~10°C colder during the Younger Dryas and that the sudden warming of 10° ±4°C that ended the Younger Dryas occurred in only about 40 to 50. years.
Figure 1. Temperature fluctuations over the past 17,000 years showing the abrupt cooling during the Younger Dryas. The late Pleistocene cold glacial climate that built immense ice sheets terminated suddenly about 14,500 years ago (1), causing glaciers to melt dramatically. About 12,800 years ago, after about 2000 years of fluctuating climate (2-4), temperatures plunged suddenly (5) and remained cool for 1300 years (6). About 11,500 years ago, the climate again warmed suddenly and the Younger Dryas ended (7).
Radiocarbon and cosmogenic dating of glacial moraines in regions all over the world and abrupt changes in oxygen isotope ratios in ice cores indicate that the Younger Dryas cooling was globally synchronous. Evidence of Younger Dryas advance of continental ice sheets is reported from the Scandinavian ice sheet, the Laurentide ice sheet in eastern North America, the Cordilleran ice sheet in western North America, and the Siberian ice sheet in Russia. Alpine and ice cap glaciers also responded to the abrupt Younger Dryas cooling in both the Northern and Southern hemispheres, e.g., many places in the Rocky Mts. of the U.S. and Canada, the Cascade Mts. of Washington, the European Alps, the Southern Alps of New Zealand, and the Andes Mts. in Patagonia of South America.
Figure 2. Temperature fluctuations over the past 15,000 years showing the abrupt cooling during the Younger Dryas and other warming and cooling periods, the Oldest Dryas (cool), Bölllng (warm), Older Dryas (cool), Allerød (warm), InterAllerød (cool), and Younger Dryas (cool).
Figure 3. Oxygen isotope record from the Greenland ice core showing an abrupt temperature drop 12,800 years ago, 1300 years of cool climate, and sudden warming 11,500 years ago.
The Younger Dryas had multiple glacial advances and retreats
The Younger Dryas was not just a single climatic event. Late Pleistocene climatic warming and cooling not only occurred before and after the YD, but also within it. All three major Pleistocene ice sheets, the Scandinavian, Laurentide, and Cordilleran, experienced double moraine-building episodes, as did a large number of alpine glaciers. Multiple YD moraines of the Scandinavian Ice Sheet have long been documented and a vast literature exists. The Scandinavian Ice Sheet readvanced during the YD and built two extensive end moraines across southern Finland, the central Swedish moraines, and the Ra moraines of southwestern Norway(Fig. 4). 14C dates indicate they were separated by about 500 years.
Figure 4. Double Younger Dryas moraines of the Scandinavian Ice Sheet.
Among the first multiple YD moraines to be recognized were the Loch Lomond moraines of the Scotish Highlands. Alpine glaciers and icefields in Britain readvanced or re-formed during the YD and built extensive moraines at the glacier margins. The largest YD icefield at this time was the Scotish Highland glacier complex, but smaller alpine glaciers occurred in the Hebrides and Cairngorms of Scotland, in the English Lake District, and in Ireland. The Loch Lomond moraines consist of multiple moraines. Radiocarbon dates constrain the age of the Loch Lomond moraines between 12.9 and 11.5 calendar years ago.
Multiple Younger Dryas moraines of alpine glaciers also occur throughout the world, e.g., the European Alps, the Rocky Mts., Alaska, the Cascade Range, the Andes, the New Zealand Alps, and elsewhere.
Figure 5. Double Younger Dryas moraines at Titcomb Lakes in the Wind River Range of Wyoming.
The multiple nature of YD moraines in widely separated areas of the world and in both hemispheres indicates that the YD consisted of more than a single climatic event and these occurred virtually simultaneously worldwide. Both ice sheets and alpine glaciers were sensitive to the multiple YD phases. The GISP2 ice core shows two peaks within the YD that match the glacial record. The absence of a time lag between the N and S Hemispheres glacial fluctuations precludes an ocean cause and is not consistent with the North Atlantic Deep Ocean Water hypothesis for the cause of the Younger Dryas, nor with a cosmic impact or volcanic origin.
Both 14C and 10Be production rates in the upper atmosphere changed during the YD. 14C and 10Be are isotopes produced by collision of incoming radiation with atoms in the upper atmosphere. The change in their production rates means that the Younger Dryas was associated with changes in the amount of radiation entering the Earths atmosphere, leading to the intriguing possibility that the YD was caused by solar fluctuations.
Why the Younger Dryas is important
What can we learn from all this? The ice core isotope data were hugely significant because they showed that the Younger Dryas, as well as the other late Pleistocene warming and cooling events could not possibly have been caused by slow, Croll-Milankovitch orbital forcing, which occurs over many tens of thousands of years. The ice core isotope data thus essentially killed the Croll-Milankovitch theory as the cause of the Ice Ages.
In an attempt to save the Croll-Milankovitch theory, Broecker and Dention (1990) published a paper postulating that large amounts of fresh water discharged into the north Atlantic about 12,800 years ago when retreat of the Laurentide ice sheet allowed drainage of glacial Lake Agassiz to spill eastward into the Atlantic Ocean. They proposed that this large influx of fresh water might have stopped the formation of descending, higher-density water in the North Atlantic, thereby interrupting deep-water currents that distribute large amounts of heat globally and initiating a short-term return to glacial conditions. If indeed that was the case, then the Younger Dryas would have been initiated in the North Atlantic and propagated from there to the Southern Hemisphere and the rest of the world. Since that would take time, it means that the YD should be 400-1000 years younger in the Southern Hemisphere and Pacific areas than in the Northern Hemisphere. However, numerous radiocarbon and cosmogenic dates of the Younger Dryas all over the world indicate the cooling was globally synchronous. Thus, the North Atlantic deep current theory is not consistent with the chronology of the Younger Dryas.
The climatic fluctuations before and after the Younger Dryas, as well as the fluctuations within it, and the duration of these changes are not consistent with a single event cause of the YD. Neither cosmic impact or volcanic eruptions could produce the abrupt, multiple climatic changes that occurred during the late Pleistocene.
Makes our current warming/cooling cycles seem puny.
Be sure and go to link at #19 and scan down to post #2 where Sunkenciv puts up an extraordinary series of links for more reading....amazing !!
The Official Website thereof ^ | prior to July 15, 2011 | Dr. Robert M. Schoch
Posted on Fri 15 Jul 2011 10:15:16 AM PDT by SunkenCiv
15,000 to 11,000 years ago Earth experienced a series of climatic fluctuations... there was a short cold spell, known as the Younger Dryas, before the final warming and... end of the last ice age. Based on Greenland ice core data, the Younger Dryas began... 10,900 B.C., and its ending... circa 9700 B.C. and may have occurred within an incredible three years... I once hypothesized that comets were responsible. A comet hitting the land or a shallow ocean, or exploding above the land's surface, scattering dust and debris into the atmosphere, would cause global cooling... This pattern fits well with the cooling at 10,900 B.C. and there is evidence of a cometary explosion over North America at this time... comets hitting deep oceans were responsible. A comet might break the thin oceanic crust, releasing heat from the hot magma beneath. Vaporized and displaced water would rain down on Earth, and tsunamis would wash across coastal areas, warming the planet... [But] Plasma hitting the surface of Earth could heat and fuse rock, incinerate flammable materials, melt ice caps, vaporize shallow bodies of water creating an extended deluge of rain, and send the climate into a warming spell. The release of pressure that follows the melting of thousands-of-meters-thick ice sheets can induce earthquakes and even cause hot rock under pressure to melt and erupt to the surface as volcanoes... The plasma event of 9700 B.C. eradicated advanced civilizations and high cultures of the time, and... could be the basis for the nearly universal myth of a Golden Age, a time when beings on Earth had mental abilities far surpassing those of later times. The 9700 B.C. event may be the original basis for the Atlantis legends; the timeframe fits well with Plato's account.
(Excerpt) Read more at robertschoch.com ...
Very nice, comprehensive thread on the glitch coming out of the Wisconsin Ice Age. Thanks!
I thought the hypothesis from the comment ( See # 10 on this thread ) made sense.
They could not take advantage of their success however because Obama traveled back in time and drove them off.
Man , ...there is just so much good stuff out there on these great internet sites.
The Cycle of Cosmic Catastrophes:
Flood, Fire, and Famine
in the History of Civilization
by Richard Firestone,
Allen West, and
|GGG managers are SunkenCiv, StayAt HomeMother & Ernest_at_the_Beach|
Thanks Ernest! I blush!
It was all those SUV’s back then.
I assume that PH- Post Hegira would be the norm by now but Moslems are not all that clear just when H was and there are several date systems stemming from it. Choosing one would upset adherents of the others.
How about 14,000 Winters ago, or many moons have passed since....
An excellent run down of the complex climate changes after the end of the recent great Ice Age. Personally, I am inclined to think the several of the major ice ages were caused by major terrestrial events. The Long Valley and Yellowstone megavolcanic events over 700,000 and 600,000 year ago come to mind. On the other hand I would not be surprised if others were begun by major boloid events. I think Firestone et al give an excellent easy to read account of events that may have caused the Younger Dryas. As one comment points out there could have been several such events relatively close in time.
The great Chesapeake Meteor event around 34 million years ago was one of several in that period. A ten mile diameter crater was found of that age off Toms River, NJ. Also Popogai (sp?), a 60 mile diameter crater in Russia has that age. On the other hand while the most recent ice age began about 125,000 ya, around 74,000 ya the megavolcano Toba left a crater 18 by 65 miles and the charts show a major downturn in temperature for that period.
In Egyptian history there is a period of perhaps 200 years prior to 2,000 BC known as the First Intermediate Period, documented in the Ipuwer papyrus housed in the Leyden (sp?) Museum. Checking on craters, I found that there were a number of significantly large boloid craters (from 5 to 14 miles in diameter) in Argentina with the right age for that period. SC has reported on the 2 mile diameter crater found in the drained Iraq Marshes also about 2,000 BC.
Detail on the eruption of Laacher See Volcano in Germany, 12,900 ya is well described in Hans-Ulrich Schmincke’s book Volcanism (2004). This Plinian eruption was slightly larger than Pinatubo. In other words there are potential a number of potential interactive forces at work influencing the Younger Dryas.
While, I think that a lot more needs to be known and worked out scientifically about anthropogenic climate influence, I think the basic thing we have to realize is that there are a number of possible potential influence on climate. Since highly educated scientists tend to be experts on volcanoes, cosmic events, climate, archaeology, or ancient history, etc, we have lacked a fully functioning interdisciplinary approach to answering such complex questions. One of the things I love about both Catastrophism and GGG is that these sites bring together a number of gifted and curious amateur science sleuths.
But that's me.
I want a fixed date from SOMEWHERE. ANYWHERE works... Jan 1st, 1970 is special for me. 1340607344
Meh... Demand a fixed time constant. It's for the wimmen.
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