 |
Earth Sciences Forum
This site is dedicated to the Earth Sciences. We are here for you to discuss issues regarding any aspect of the Earth sciences, at all levels of knowledge. Questions are welcomed, as are open scientific debates. Enjoy!!!
|
| View previous topic :: View next topic |
| Author |
Message |
Andre
Joined: 21 Jul 2007
Posts: 298
Location: Germany - The Nederlands
|
 Posted: Sun Nov 04, 2007 2:23 pm Post subject: Where is the Dryas anyway? |
 |
|
Stupid question? let's see.
Spencer Weart has made a minute research to paleoclimatologic records. he says about the Dryas octopetala pollen:
| Quote: | | The most prominent oscillation — already noticed in glacial moraines in Scandinavia around the turn of the century — had begun with a rise in temperature, named the Allerød warm period. This was followed by a spell of bitterly cold weather, first identified in the 1930s using Swedish data. It was dubbed the "Younger Dryas" period after Dryas octopetala, graceful but hardy Arctic flower whose pollen gave witness to frigid tundra. (The glacial period that preceded the Allerød was the "Older Dryas.") The Younger Dryas cold spell was followed by a more gradual warming, ending at temperatures even higher than the present. In 1955 the timing was pinned down in a study that used a new technique for dating, measuring the radioactive isotope carbon-14. The study revealed that the chief oscillation of temperatures had come around 12,000 years ago. The changes had been rapid — where "rapid," for climate scientists at mid-century, meant a change that progressed over as little as one or two thousand years. Most scientists believed such a shift had to be a local circumstance, not a world-wide phenomenon. There were no data to drive them to any other conclusion, for it was impossible to correlate sequences of varves (or anything else) between different continents. That would only become possible when radiocarbon dating overcame the many inaccuracies and uncertainties that beset the technique in its early years.(7*) |
The ref being:
| Quote: | Outside Scandinavia, carbon-14 dating of trees overridden by the North American ice sheet showed the front had advanced and retreated by up to a kilometer a year between 13,600 and 12,200 years ago. Flint (1955)
Flint, Richard F. (1955). "Rates of Advance and Retreat of the Margin of the Late-Wisconsin Ice Sheet." American J. Science 253: 249-55. |
Wait a minute, what was this again with the carbon dating problems and when were those really sorted out? That was about the early 1990s when varve counting versus carbon dates from a Japanese lake Suigetsu. There is no way for Flint in 1955 to have corrected the dates to the appropriate calendar age!!
So those 12000 carbon years would nowaday be about 13,800 calendar years and that would be shortly after the gigantic Bolling spike at 14,500 years ago:
So if we want to find the orginal dryas pollen back in Sweden, we might not find them in the Younger Dryas but much earlier.
I found this:
Main pollen inventory from six Swedisch lake cores, stacked vertically. The only reference of "dryas" is in the orange cell in Lake Bolmen around 14,000 years ago. None whatsoever in the Younger Dryas.
Incidentely the yellow cells contain the genus Empetrum, crow berry, a predominantly sub arctic species of boreal forests and wet tundras. And were are those? Not in the Younger Dryas but both in the preceding Allerod and the following Preboreal. The species form the Younger dryas have a too broad range to judge temperatures, but we see several trees (betula - birch, and juniperus) so we are below the treeline.
But the big problem is: where is the mythical Dryas that named the Younger Dryas?
_________________
Moderator of http://tech.groups.yahoo.com/group/climatesceptics/
"Don't worry about the world coming to an end today. It's already tomorrow in Australia."
Charley Brown |
|
| Back to top |
|
 |
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
|
|
FAQ
Search
Memberlist
Usergroups
Join! (free) 
Profile
Log in to check your private messages
Log in
