Earth Sciences Forum

Andre

So when did it start and what would that matter?
That's a vital question.

Wikipedia wasn't sure:

scpg02 · Joined: 22 Jul 2007 Posts: 221 Location: Sacramento

I feel lost. Basically what your saying is that what they have been using to denote temperature was really showing precipitation or lack there of.

This doesn’t surprise me. I have always believed that the science follows the politics rather than the other way around. I’ve seen it too many times when it comes to property/water rights, logging, grazing etc.

Andre · Posted: Mon Aug 20, 2007 8:56 pm Post subject:

I can imagine that, but I'm sure that the mistake here, is essentially politics free. Isotope thermometry started long before the global warming hype. Dansgaard was the inventor. First publishing was 1964.

Richard Alley writes in his famous Two Mile Time Machine:

Essan · Joined: 30 Jul 2007 Posts: 11 Location: Evesham, Worcs

The only way such a sudden drop in temp seems to have been explained, is by a sudden switch off of the NAD ...... but there are question marks over why this happened and even if it actually happened at all.

Couple of questions: would a switch off of the NAD cause a reduction in precipitation in the N Atlantic regions?

What other causes might there be for a 'sudden' reduction in precipitation?
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Andre · Posted: Tue Aug 21, 2007 3:08 pm Post subject:

Andre · Posted: Wed Aug 22, 2007 9:31 am Post subject:

let's go back to the start of the Younger Dryas, because it's essential if we talk 12,900 or 12,680 Cal years BP. Because there is that last Allerod spike in between:

They have invented an interesting extra terrestrial event for the cause of the Younger Dryas here:

Firestone R, et al, New Insights into Younger Dryas Climatic Instability, Mass Extinction, the Clovis People, and Extraterrestrial Impacts

Andre · Posted: Wed Aug 29, 2007 2:22 pm Post subject:

pasting a part of the paper. This is essential. It shows that the wide spread glacial re-advances occured just before the Younger Dryas:

Dating the transition of the Allerod to the Younger Dryas

Latecommer · Joined: 26 Jul 2007 Posts: 45 Location: Central California

Andre
Could you please give us a quick opinion on what ice cores are good for and what they are not? I have been reading much about how they do not serve as a very good proxie for co2 levels. Do you agree with that POV?

Regards
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Andre · Posted: Thu Aug 30, 2007 10:06 am Post subject:

HighPlanesDrifter · Posted: Wed Oct 24, 2007 4:39 pm Post subject: YD discussion at RC

Andre,

I thought about you this morning when I read this post over @ RC. You might consider posting some of your theories about the YD (such as precipitation pattern change rather than temperature change) and questions (such as what papers make the claim for finding Dryas octopetala pollen from that period?) in this thread. The folks at RC would be much more qualified to address your thoughts than I am.

Cheers, hpd

PS. You have the option to link to this site through your name. Should you choose to, I imagine it would increase the traffic here in your YD section substantially.

Andre · Posted: Thu Oct 25, 2007 9:25 pm Post subject:

Thanks HPD

My reply is #32

This is the rebuttal NQ and I prepared for the Firetone impact hypothesis:

Andre · Posted: Tue Feb 05, 2008 9:42 am Post subject:

This graph shows the reason of the Younger Dryas controversy. On top two compilations of many paleo botanic studies dividing the Younger Dryas in two parts, a wet cold first part from about 11,000 ¹⁴C years BP to ~10500 ¹⁴C years BP. Carbon years (¹⁴C years BP) on the upper scale. This is followed by a second warmer but drier part. On the lower scale the counted (calendar years) showing two isotope records with high correlation, the Greenland GRIP ice core and a varve counted core from the Ammersee in Southern Germany in the middle of the area of the inventarisation of Isarin and Bohncke.

So if you let the Younger Dryas start at the red vertical line around 12900 calendar years ago, you capture the cold phase and you can argue that the YD was about a sudden return to cold glacial conditions. However the isotopes went the other way, up instead of down.

If you start at the isotope drop around 12650 calendar years ago, the alleged start of the cold phase of Younger Dryas at the vertical bold black line, you won't find any sudden temperature drop, not even a cold Younger Dryas. So this is what caused the controversy. Not calibrating all events on the same time scale and the abbaration of the GISP-2 ice core.
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Andre · Posted: Thu Feb 07, 2008 10:51 am Post subject:

Meanwhile there is a new chronology for the GRIP/NGRIP/Dye-3 ice cores in Greenland.

The publication: http://www.gfy.ku.dk/~www-glac/papers/pdfs/220.pdf

The data: http://www.gfy.ku.dk/~www-glac/da...CC05_NGRIP_GRIP_20y_27nov2006.txt

Now I converted the "b2k" base of their GICC05 timescale (2000AD) to the traditional 1950AD to stay compatible with the rest. Then we get this for the start of the Younger Dryas:

The graph shows 100 years smoothed data, for comparison the original GRIP data are visible showing that it's rather hard to plot an arbitrary mid point as starting point of the YD.

Anyway we now get values around 12,780 cal Year BP, over 100 years older than previously. Why?

Notice in the text of the data: