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Andre
Joined: 21 Jul 2007
Posts: 298
Location: Germany - The Nederlands
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 Posted: Sun Jul 29, 2007 2:04 pm Post subject: Exhibit #6, The Younger Dryas and North America |
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The objective of the "Exhibit-#n-The-Younger-Dryas-and .......,"-threads is to investigate for ourselfs what evidence is available to judge about the alleged cold conditions of the Younger Dryas.
It appears that North America shows more variation and contradictions than elsewhere.
This fresh study appears to be in line with the general trend, dry but not indicated as cooler:
Deglacial climate variability in central Florida, USA
Willard, D.A., C.E. Bernhardt, G.R. Brooks, T.M. Cronin, T. Edgar and R. Larson, 2007: Deglacial climate variability in central Florida, USA; Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 251, Issues 3-4, 8 August 2007, Pages 366-382
| Quote: | Abstract
Pollen and ostracode evidence from lacustrine sediments underlying modern Tampa Bay, Florida, document frequent and abrupt climatic and hydrological events superimposed on deglacial warming in the subtropics. Radiocarbon chronology on well-preserved mollusk shells and pollen residue from core MD02-2579 documents continuous sedimentation in a variety of non-marine habitats in a karst-controlled basin from 20 ka to 11.5 ka.
During the last glacial maximum (LGM), much drier and cooler-than-modern conditions are indicated by pollen assemblages enriched in Chenopodiaceae and Carya, with rare Pinus (< 10%). Pinus pollen increased to 20–40% during the warming of the initial deglaciation ( 17.2 ka), reaching near modern abundance (60–80%) during warmer, moister climates of the Bølling/Allerød interval (14.7–12.9 ka). Within the Bølling/Allerød, centennial-scale dry events corresponding to the Older Dryas and Intra-Allerød Cold Period indicate rapid vegetation response (< 50 years) to climate variability. The Younger Dryas (12.9–11.6 ka) was characterized by two distinct phases: slightly drier than the peak Bølling/Allerød between 12.9 and 12.3 ka and much drier from 12.3 to 11.5 ka. The Tampa Bay record of deglacial atmospheric temperature and moisture can be correlated with other paleoclimate records in the North Atlantic region and has implications for climate-forcing by ice-sheet fluctuation, thermohaline circulation, and atmospheric circulation. |
emphasis mine
Notice the initial warming also way before the Bolling Allerod. And indeed if you start the Younger Dryas too early (12,900 years ago instead of 12,665 Meerfelder maar varve years ago) then the first part certainly is wetter.
More later for some contrasts.
See also
The Younger Dryas exhibits
Exhibit #1, The Younger Dryas and the Meerfelder maar
Exhibit #2, The Younger Dryas and Mediterranean region
Exhibit #3, The Younger Dryas and South greenland
Exhibit #4, The Younger Dryas and Glaciation
Exhibit #5, The Younger Dryas and the Mystery interval
Exhibit #6, The Younger Dryas and North America
Exhibit #7, The start of the Younger Dryas
Exhibit #8, The Younger Dryas and the Siberian Steppes
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Last edited by Andre on Tue Aug 21, 2007 7:18 pm; edited 1 time in total |
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Andre
Joined: 21 Jul 2007
Posts: 298
Location: Germany - The Nederlands
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| Posted: Thu Aug 09, 2007 8:14 pm Post subject: |
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Here is such an outlier:
| Quote: | | Based on speleotem growth Polyak et al 2004 find in New Mexico that the Bølling (14,500-14,000ka) was wetter, the Allerød (14,000-12,700Ka) was supposed to be arid whilst the Younger Dryas was supposed to be wetter again. This is at odds with most proxies, although regional variation is certainly not to be ruled out. It should also be noted that the 230/232Th dating is depending on whether or not the assumptions about initial 230/232Th ratios are correct under several additional fractionation processes. |
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Latecommer
Joined: 26 Jul 2007
Posts: 45
Location: Central California
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| Posted: Sun Aug 12, 2007 3:09 pm Post subject: |
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Very nice work Andre, Is there any estimate of when you will release the entire work?
D
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Andre
Joined: 21 Jul 2007
Posts: 298
Location: Germany - The Nederlands
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| Posted: Sun Aug 12, 2007 9:37 pm Post subject: |
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Well, let's see.
The outline is ready, compilation of publications as here in the exhibits is about 50-75%. That takes a lot of time. present size 22 pages text; of summing up facts, exclusive 16 pages of references. it will grow some more.
I really need to quantify the deuterium excess of Masson Delmotte et al 2005 Sciencemag to show that this is consistent with aridity. I guess it can be done.
Several weeks I guess to have the first draft ready. One more generation to get it published. Of course there are major hurdles. Science progresses one death at the time.
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Andre
Joined: 21 Jul 2007
Posts: 298
Location: Germany - The Nederlands
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| Posted: Tue Aug 21, 2007 7:05 pm Post subject: |
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A few more from the concept paper:
| Quote: | Pienitz et al 2000, define an “interval II (c. 10 500–8100 yr BP)” and contend that: The early Holocene period showed initially high diatom-inferred salinity values (|20 g L-1), probably driven by low effective moisture and higher temperatures. However 10,500 yr BP calibrates to 12590 Cal BP . Consequently their interval II -higher temperature -appears including most of the Younger Dryas.
Kneller M. and D. Peteet, 1999: find multiple climate oscillations from a Central Appalachian Pollen and Macrofossil Record but these do not coincide with the Younger Dryas
Ager (2003) questions the nature of the Younger Dryas, seeing a invasion of Populus between 11 ka and 9,5 ka BP (12.9 – 10.7 ka cal BP)
Clark 2003 observes that the Sierra Nevada remained largely or entirely free of glacier ice, including during the Younger Dryas (YD) chronozone
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