6 replies to this topic

[sepulchrave]

To paraphrase an article on Ars Technica:

It seems like some climatologists (Mann, Fuentes, and Rutherford) are suggesting that large-scale volcanic activity can prevent an entire year of tree growth, thus changing the chronology of tree rings (in a paper published in Nature Geoscience here).

Some dendrochronologists reject this assertion (in a paper published in Nature Geoscience here).

If I recall correctly, Doug1o29 has some experience with dendrochronology, do you have any comments on this debate?

(And it would be nice if all other commenters could avoid the usual flame war about anthropogenic climate change for once...)

[questionmark]

you mean locally? Yes that is a known phenomenon in Kamchatka, for example, but surely not global. If there is a large local event (like Krakatau) it should be taken into account.

[Doug1o29]

sepulchrave, on 04 February 2013 - 07:12 PM, said:

To paraphrase an article on Ars Technica:

It seems like some climatologists (Mann, Fuentes, and Rutherford) are suggesting that large-scale volcanic activity can prevent an entire year of tree growth, thus changing the chronology of tree rings (in a paper published in Nature Geoscience here).

Some dendrochronologists reject this assertion (in a paper published in Nature Geoscience here).

If I recall correctly, Doug1o29 has some experience with dendrochronology, do you have any comments on this debate?

(And it would be nice if all other commenters could avoid the usual flame war about anthropogenic climate change for once...)

Anything that puts a tree under extreme stress can cause it to suspend growth.  That could be severe cold, severe drought, loss of a major part of its crown to wind or ice, or even just getting bent too far.  Trees growing near timberline can suspend growth en masse.  But there are usually a few around that keep growing.  These can be used to determine which rings are missing in other nearby trees.

If you pretend that trees don't do this and you make an estimate of past temperatures based on it, you get a higher temperature than if you included the missing rings.  Mann noted that if he did not include the zeroes, the temperature estimate matched up nicely with previous estimates of high-latitude temperatures during the Medieval Warm Period.  Thus, he assumed that there had been a mistake in reading the cores.  A small army of dendrochronologists are getting ready to draw and quarter him as a result.  It will be interesting to see how this plays out.

In this case, I think we just have to live with the fact that not all estimates of past temperatures are going to agree perfectly.
Doug

[sepulchrave]

Thanks for the insight, guys!

[Raptor Witness]

Doug1o29, on 04 February 2013 - 10:06 PM, said:

Anything that puts a tree under extreme stress can cause it to suspend growth.  That could be severe cold, severe drought, loss of a major part of its crown to wind or ice, or even just getting bent too far.  Trees growing near timberline can suspend growth en masse.  But there are usually a few around that keep growing.  These can be used to determine which rings are missing in other nearby trees.
Doug

I have a large collection of petrified wood from the Mississippi Alluvial plain. I wonder how hard it would be to date some of it, as a result of the hard work done in this area of science.

I might be willing to share some to a starving scientist who is trying to piece together the past.

[Doug1o29]

Raptor Witness, on 07 February 2013 - 08:47 PM, said:

I have a large collection of petrified wood from the Mississippi Alluvial plain. I wonder how hard it would be to date some of it, as a result of the hard work done in this area of science.

I might be willing to share some to a starving scientist who is trying to piece together the past.

If it is truly petrified, getting an exact date is all but hopeless as no tree-ring calendars go back far enough to provide a cross date.  Such a problem would occur at Petrified Forest, for example.  In this case, you could still produce a free-floating chronology - a series of ring widths suitable for calculating rainfall, for example, except that you wouldn't know which years those were.

With sub-fossil wood, you might be able to match it to an existing chronology which would give you the exact years.  There is a chronology currently being put together for the Mississippi River system - the northern part of it - that will reach back 12,000+ years when complete.  Parts of it are useable right now, except that it hasn't been published.  Most of the samples being used have been recovered from permanently-flooded sites where the wood is protected from decay.  The problem is that when it is exposed to the air, the wood quickly decomposes, so special efforts have to be made to preserve it.

I am trying to solve a similar problem right now.  A guy was cleaning out a pond and pulled out a number of old sawlogs, which he left on the bank to dry.  They all have dry rot.  If I can figure out how to stablilize them, I might be able to produce a chronology from them.  Stay tuned.

If you want to see what we can do, PM me.

Your name wouldn't be Michael or Richard, would it?
Doug

[Raptor Witness]

Doug1o29, on 07 February 2013 - 11:21 PM, said:

If it is truly petrified, getting an exact date is all but hopeless as no tree-ring calendars go back far enough to provide a cross date.  Such a problem would occur at Petrified Forest, for example.  In this case, you could still produce a free-floating chronology - a series of ring widths suitable for calculating rainfall, for example, except that you wouldn't know which years those were.

If you want to see what we can do, PM me.

Your name wouldn't be Michael or Richard, would it?
Doug

This is opalized, mostly. The cool thing is some of it is of a natural color, appearing like real pine, for example. This is very rare in my experience, but I have limited qualities of this.

I'll try and take a picture for you of some, and publish them here. I have tons of the stuff, of all colors, shapes, and sizes.

I also have some bark, I believe, which is cool.  I have an indian tool made out of petrified wood, which is really cool. I think it may be a fire starter, or used for grinding small stuff, perhaps medicine. I'm not sure, it's a bit of a mystery, but fairly certain it's been worked by man.

Edited by Raptor Witness, 07 February 2013 - 11:34 PM.