Comments on: Geological Perspective #2

By: TCO

TCO — Mon, 19 Sep 2005 03:50:03 +0000

1. Do you buy the O18 proxy in these bugs?

2. Any danger that GW will plip us back into the Pliocene? (I would like it actually…alligators.)

By: John G. Bell

John G. Bell — Tue, 07 Jun 2005 20:00:12 +0000

Kenneth H. Schatten was almost a dozen years ahead of me on this. See Heliographic latitude dependence of the Sun’s irradiance, Journal of Geophysical Research, vol. 98, no. A11, p. 18,907-18,910

abstract: http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993JGR….9818907S&db_key=AST

Seems like being on the sun’s spin axis is a cool place to be. More so 850Kys ago?

By: John G. Bell

John G. Bell — Fri, 27 May 2005 17:23:49 +0000

Re #5; The inclination cycle would expose the earth more to the sun’s poles. The sun’s poles never get sunspots. Perhaps sunspots are new to the last 850Kyrs? You wouldn’t think the impact would be large enough. That the average irradiance could be so changed by 1.5 degree more or less of a solar pole view. A change in irradiance over solar latitude away from uniformity 850kys ago might do it if it was large enough.

I had confused axial tilt with precession in my earlier comments, so much of what I said belongs in the dust bin. Andre you are much too kind .

By: John G. Bell

John G. Bell — Fri, 27 May 2005 14:41:26 +0000

Andre, Thank you for link to the Muler article.

By: John G. Bell

John G. Bell — Fri, 27 May 2005 13:54:31 +0000

Andre, some of the information on Milankovitich theory I was working with came from

http://www.usask.ca/geology/classes/geol206/glacial.html

It gives the cycle time for eccentricity changes as 92K to 100K years and changes in the tilt of the earth’s axis a cycle time of 41k years. de Gariedel-Thoron in the Nature article doesn’t mention Milankovitich but has in figure 2 of the article a couple of spectral analysis graphs of sea surface temperatures. One from 6 to 850kyrs, the other from 900 to 1,748kyrs ago. What they show is that the 100kyr cycle most prominent in the former and the 41kyr cycle in the latter. He has the 23kyr cycle also marked which is related to the precession of the equinoxes. The sliding of the Antartic continent over the pole saw the pole dive to the center of the Antartic land mass around 850kyrs ago. I wondered if that change might explain the switch from 41kyr to 100kyr glacial cycles 850kyrs ago. Back to the library! Thanks

By: André Bijkerk

André Bijkerk — Fri, 27 May 2005 06:47:41 +0000

Re #4; John, on your #25 mentiones the eccentricity cycle as predominant for the 100Ky. I know, you can find multiple textbook explications about this but still I don’t think it isn’t. The original Croll-Milankovitch eccentricity cycle is composed of two main components, the stronger cycle 410Ky and the weaker 90Ky. So it’s a mystery how it changed in the books to 100Ky after the discovery of that benthic foram signal and of course echoed in the Antarctic ice cores, 420Ky in Vostok, (Petit et al 1999) and 740Ky in EPICA Dome-C (Jouzel et al 2004). Richard Muller had another elegant hypothesis about this behavior, a cosmic dust band around the sun that the Earth would enter every 100Ky due to an inclination cycle.

http://muller.lbl.gov/papers/sciencespectra.htm

Now, dust indeed shows in the ice cores during the deepest pits in the cycles but closer investigation shows that it all Earth related, not cosmogenic. There is no other evidence like increased cosmogenic radioactivity so this hypothesis remains very tentative. Moreover if you really zoom into the abundant available details details of the last “termination” things are definitely not what they seem to be. There is still a lot to resolve.

By: John G. Bell

John G. Bell — Thu, 26 May 2005 20:59:07 +0000

Andre, see my comments: http://www.climateaudit.org/index.php?p=191 #24 & #25. I think all sorts of hints can be found in that Nature article. I’ll add to #25 to say that an
Antartic bay, I forget which now, might have been broken up every 41K years before 850k years ago. This could be caused by sea level increase from melting, perhaps in other locations, lifting the ice off the floor of the bay. The pole was close to the bay before 850k years ago, but it has since moved inland. Warning I probably don’t know what I’m talking about, I have no formal education in this. But do look at the article for the data content.

By: Paul Gosling

Paul Gosling — Thu, 26 May 2005 10:22:22 +0000

Looking on this scale the decline in temperature from 4 My BP looks almost linear. This would suggest the cause is a gradual change, such as the rise of the Hymalaya, or declining atmospheric CO2, rather than a sudden change, such as the closing of the Panama isthmus.

By: Andre Bijkerk

Andre Bijkerk — Thu, 26 May 2005 07:37:13 +0000

The most recent benthic stack that is supposed to represent climate is of Lisiecki and Raymo http://www.maureenraymo.com/current_projects.php#millennial

The graph is actually giving the variation in oxygen isotopes (d18O) of certain ocean floor dwelling (benthic)foraminifera, that are analysed from ocean sediment cores. some go back to much older strata. So if an ice sheet is building up it is made of light water with more 16O, because of the fractination during the evaporation. More 16O water evaporates so more 18O water stays behind. Now if the evaporated water does not return because it is used for ice sheet building then the amount of remaining 18O water in the oceans increases. So more 18O in the forams means: either the local water is colder or there is more 18O in the water, which means that there are polar ice sheets which means that it is cold.

However, there is a lot of “if-it-rains-the-streets-are-wet. The-streets-are-wet-so-it-rains” reasoning here. Foram d18O is also dependent on salinity and acidity, so a current change or other conditions changing may also cause d18O changes in forams. Then, ice sheets may only be building if the poles are land on a hundred million years scale. And due to of course of lot of plate tectonic every now and then a continent swarfs over the poles. Then a ice sheet may build but does it mean that the global temperature changes? I think not (that’s also regarding that greenhouse – ice house hypothesis in the other blog.

back to the benthic stack. Note also the big change around 900,000 years ago when the predominant weak cycle frequency shifted from ~41,000 years to the strong ~100,000 signal. The former is thought to be related to the obliquity cycle of the Earth spin axis. For the latter all current explanations do not suffice. This is a beautiful detective plot, waiting to be solved.

By: Larry Huldén

Larry Huldén — Wed, 25 May 2005 07:31:34 +0000

Commenting on:
“It’s interesting that the variations in the Pliocene on a millennial/10-millennial scale were much smaller than in the Pleistocene”
It’s also interesting that nowadays the annual variations in the temperatures are much smaller in the tropics than in the north. On the other hand the recent increasing temperature trend (if really existing) is lower in the north than in the tropics, because summer temperature trend seems to be somehow buffered in the north. In Finland the summer temperature trend seems to correlate with northern hemispheric tree rings. In that way the tree rings seem to respond correctly to the measured temperatures in the north. They haven’t grown more because temperatures haven’t increased.
Larry Huldén