Happy Perihelion: Closest Approach to the Sun!

[Xnn]

Not quite yet I know, but as everyone else is wishing happy New Years, it seems to be the season to wish good will.

On or around the 4th of January we (everyone on Earth that is) will be at our closest to the sun. That the calendar year just started is only a coincidence. Due to orbital variations, our date of closest approach varies a little bit over time. That is the time/season of perihelion will gradually shift over thousands of years. Earth's axis is slowly but continuously changing, with a cycle of approximately 25,765 years.

Currently the distance between the Earth and sun varies between 98.3– 101.7% of its average distance. At its average distance sunlight amounts to about 1365.5 watts/m^2. Being at perihelion, the sun’s intensity is greater of course. However, since intensity varies by the inverse square of the distance, its intensity is now about 1412.3 watts/m^2. That is a 6.7% increase over where it was just last summer!

Ever wonder how our climate would be if perihelion occurred in June instead of January? It won’t happen for another 12,000 years or so, but when it does Northern hemisphere summers would be warmer and winters colder. Just the opposite will happen in the southern hemisphere and there is another difference too. It not just that most of us live in the north, but there is much more land than the south.

The extra land of the north provides a big platform for seasonal snow, and snow feeds back into the climate through the change in albedo. That is the amount of sunlight that is absorbed. Less snow means more sunlight is absorbed and more warmth. More snow leads to less absorption and cooler temperatures.

 

[Andre]

Although the precession cycle of the equinoxes amounts to 25,765 years, this precession cycle of the aphelion/perihelion is a mix of cycles between 19,000 years and 23,000 years. The difference between the two is caused mainly by Jupiters gravity, shifting the perihelion/aphelion.

http://www.emporia.edu/Earth'sci/student/howard2/theory.htm

 

[marcus]

Sure we should have a Perihelion Party!
And there should be a lifesize papier mâché figure of Hans Kepler to sit at the table.
He is Mr. Perihelion of course because if it weren't for ellipses we wouldn't ever have a perihelion, it would just be dumb circles all the time.

I think you had a good idea to wish us a Happy Perihelion and I wish you one too, and fun and good fortune throughout the Orbit!

We need to be more aware of the sun. And the other stars as well.

Maybe to save trouble making the papier mâché figure I could dress up as Kepler. I always wanted to do this...

 

[Mammo]

Currently the distance between the Earth and sun varies between 98.3– 101.7% of its average distance. At its average distance sunlight amounts to about 1365.5 watts/m^2. Being at perihelion, the sun’s intensity is greater of course. However, since intensity varies by the inverse square of the distance, its intensity is now about 1412.3 watts/m^2. That is a 6.7% increase over where it was just last summer!

How does this post relate to the 100-kyr eccentricity cycle? After reading 'The Two Mile Time Machine' by Richard Alley, I was left with the impression that the insolation difference of a varying Earth-Sun distance of around 6% was not enough to explain the cycle of the ice ages. Can someone please enlighten me if I'm simply being stupid.

 

[Xnn]

Mammo;

Hopefully, I can figure out how to include attachments here.

About 2.5 million years ago periodic ice ages began.
Originally, the warm periods were on 41,000 year cycles.
Over time, the warm periods degraded to 100,000 year cycles.

The Earth's orbit basically has 20,000, 41,000 and 100,000 year cyles to it.
There is not much difference between the 41,000 and 100,000 year cycles.
So, it has been a struggle to figure out why the Earth did the transition.
The latest that I've heard is that CO2 levels were just getting too low and the Earth appeared to be gradually slipping into a permanent ice age.

Here's a useful image and an good science article.

 

[Andre]

But it's a bit different.

The big main eccentricity cycle are http://books.google.nl/books?id=s78sAPvQjN0C&pg=PA66&lpg=PA66&dq=eccentricity+cycle+413,000&source=bl&ots=P3XwkpkuWL&sig=h9GsEc4ZXmpxZ2UwQdycHfw8-3w&hl=en&sa=X&oi=book_result&resnum=9&ct=result . (413 ka and 100ka)

The former is stronger but does not show up at the Maritieme Isotope Stages, the latter is weaker but seems to dominate the cycles. I have never heard a satisfactory explanation for that.

There are more events that could be tied to the switch from the 41ka world to the 100ka world, the magnetic reversal from Matuyama to Brunhes chron (730 Ka ago). the latter being much more variable than the former and the Stilostomella extinction during the Mid Pleistocene.

 

[hypatia]

I'm making a vast array of perihelion foods. Cooked outside on a solar collector while wearing sunglasses. And if I have any time left, I may carve a spirit stone, and line it up with my house and the angle of the sun. Just so the archeologist's have something to do, in a 1,000 years from now.

 

[Xnn]

Andrea;

The Huybers paper explains that glaciers/ice caps are sensitive to insolation integrated over the duration of the summer. And integrated summer insolation is primarily controlled by obliquity and not precession, which is on a 40K yr cycle.
However, as the Earth cooled during the Pleistocene, the 40K cycle heat eventually wasn't always enough to triger glacial termination.

Sometimes it wasn't until the 2nd or 3rd cylces that the glacial sheets would be sufficiently melted. 80K and 120K averaged out to 100K.

So, there really is no pure 100K cycle. It just happens to be the average value over the last million years of 2 or 3 40K cycles.

 

[Andre]

Andrea;

You're Italian?

The Huybers paper explains that glaciers/ice caps are sensitive to insolation integrated over the duration of the summer. And integrated summer insolation is primarily controlled by obliquity and not precession, which is on a 40K yr cycle.
However, as the Earth cooled during the Pleistocene, the 40K cycle heat eventually wasn't always enough to triger glacial termination.

Sometimes it wasn't until the 2nd or 3rd cylces that the glacial sheets would be sufficiently melted. 80K and 120K averaged out to 100K.

It would be nice to have a ref to see what they did to validate that hypothesis. For instance if we look at the over familiar See saw here:

[PLAIN]http://www.climateactionnetwork.ca/images/charts/vostok-ice-core.jpg

We note pretty low conditions around 50-25ka. However if we compare that with other climate data, things look much different, take for instance North Siberia in http://epic.awi.de/Publications/Hub2004a.pdf

we see a distinct dry an warm period in the Middle Weichselian MW-I and MW- II("Karginian") warmer summers than at present, evidently the mid Weichselian glaciation was long forgotten

 

[Xnn]

You're Italian?

No, just a typo. Sorry.

We note pretty low conditions around 50-25ka. However if we compare that with other climate data, things look much different, take for instance North Siberia. we see a distinct dry an warm period in the Middle Weichselian MW-I and MW- II("Karginian") warmer summers than at present, evidently the mid Weichselian glaciation was long forgotten.

25-50ka NH glaciation was much greater than the present.
Globally dryer conditions existed; which should include North Siberia.

Centered around about 30 and 50ka, perihelions occurred during the summer.
So, during those periods, one could expect Siberia to have somewhat warmer summers.
Not as warm as 10ka when perihelion and obliquity worked together, but warmer.

One the other hand, centered around about 41ka, perihelion occurred in winter as it does now, but with different eccentricity. Not sure how eccentricity would work out 41ka. Possibly it leads to warmer summers, but it depends somewhat on actual latitude. Siberia is a very large area. Not all of it is at 65N.

Also, as the Huyber paper points out, glaciers respond to intergrated insolation.
Short hot summers are not as important as longer warmer summers.
The Hubbertin paper may be focusing on fauna, which probably respond differantly.

 

[baywax]

Excellent thread!

Another excuse to celebrate. Perfect!

 

[Andre]

...The Hubbertin paper may be focusing on fauna, which probably respond differantly.

Note that the climate analysis is based on insect remains. Several insects are supposed to reside in well defined biotopes including climate.

...25-50ka NH glaciation was much greater than the present...

For testing statements like that, perhaps we should also have a look in the http://www.thecanadianencyclopedia.com/index.cfm?PgNm=TCE&Params=A1ARTA0010506

BLUEFISH CAVES (I-III) is one of the most important cave sites in Canada because it contains: (1) evidence of some of the earliest people in North America (from about 25 000 to 10 000 years ago)*;...

..Most of the bones are Late Wisconsinan (about 30 000 to 15 000 years ago)* in age. One of the most spectacular specimens from the area is a partial Yukon horse carcass from Last Chance Creek that dates to about 26 000* years ago

Ice age vertebrate remains near Dawson City are mainly exposed during placer mining for gold. Nearly 70 fossil localities are recorded in the region. Most of the bones are Late Wisconsinan (about 30 000 to 15 000 years ago)* in age.

And more, http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VGS-4GDSF04-1&_user=10&_coverDate=01%2F31%2F2006&_rdoc=3&_fmt=high&_orig=browse&_srch=doc-info(%23toc%236046%232006%23998579999%23606772%23FLA%23display%23Volumes)&_cdi=6046&_sort=d&_docanchor=&view=c&_ct=23&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=6aa2a25bfa4e0d16bce862cdf4458bc1

..Nine AMS radiocarbon ages place these data between ca. 18,880–16,440 14C yr BP (22,313–19,597 cal. yr BP). These data indicate that xeric steppe, rich in bunchgrasses Poa and Elymus, Artemisia frigida and diverse forbs was interspersed within a mosaic of local vegetation types...

Our paleoecological data reflect environments inhabited by the diverse late Pleistocene Bluefish Caves fauna, including woolly mammoth, horse, steppe bison, and saiga antelope.

Of course we all have the lonely mammoth on our retina's dragging itself through the snow in a howling blizzard, a pack of hungy wolves in his wake, but horses? and antelopes? Doesn't really suggest extensive glaciation, does it?

*Note that Paleontologist aways talk carbon dates So calibration makes it a few thousand years older

 

[Mammo]

Mammo;

Hopefully, I can figure out how to include attachments here.

About 2.5 million years ago periodic ice ages began.
Originally, the warm periods were on 41,000 year cycles.
Over time, the warm periods degraded to 100,000 year cycles.

The Earth's orbit basically has 20,000, 41,000 and 100,000 year cyles to it.
There is not much difference between the 41,000 and 100,000 year cycles.
So, it has been a struggle to figure out why the Earth did the transition.
The latest that I've heard is that CO2 levels were just getting too low and the Earth appeared to be gradually slipping into a permanent ice age.

Here's a useful image and an good science article.

Thanks Xnn for the excellent clarification. It's now a lot clearer.

 

[Xnn]

Of course we all have the lonely mammoth on our retina's dragging itself through the snow in a howling blizzard, a pack of hungy wolves in his wake, but horses? and antelopes? Doesn't really suggest extensive glaciation, does it?

Are you of the belief that glaciation 25-50 Ka in the NH was less extensive than the present??

 

[Andre]

Are you of the belief that glaciation 25-50 Ka in the NH was less extensive than the present??

I try never to be "in belief". I merely test hypotheses and at stake currently is if the isotope see saw in the benthic stacks, indeed represents ice (sheet) volume according to the direct evidence and as demonstrated here, it does not look good so far.

Moreover the formulation "less extensive than the present" is a strawman, the statement was:

25-50ka NH glaciation was much greater than the present.

Perhaps it wasn't that 'much' enough to satisfy the isotope - ice sheet hypothesis

 

[Xnn]

I try never to be "in belief".

Then are you a perpetual skeptic?

That is no beliefs, just criticisms?

 

[Andre]

It's irrelevant but see my signature what I stand for.

Just trying to validate theories like this this.

However this one was develloped while there was still notion of a large http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VBC-41XM80M-14&_user=10&_coverDate=01%2F31%2F2001&_alid=848412560&_rdoc=1&_fmt=high&_orig=search&_cdi=5923&_sort=d&_docanchor=&view=c&_ct=1&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=5a173137505a6a5a81b6f2ad28b44042.

 

[baywax]

Can any of GW be explained by the cycle of the perihelion?

We are getting down to -50 degrees C in our central provinces (CDN)

We've had more snow on the West Coast than any other time for
the season, since 40 years ago. The all time record has been broken.

 

[Xnn]

baywax;

The perihelion has been proceeding in the wrong direction to explain global warming.
It moves very slowing and since it is occurring in January, one would expect summer to be cool enough in the NH for most glaciers to accumulate ice.

However, there was an increase in total solar irradiance upto about 1945 that can explain the warming of the 1930's and early 40's. Since that time, solar irradiance has been on the decline.

 

[Xnn]

Andre;

Skepticism is good, but too much of anything is too much.

Anyhow, If you check around I'm sure you will find that there are several species of horses and antelopes well adapted to cold climates. In fact, there are still ape like creatures from tropical Africa that settled in the Arctic.

 

[Andre]

Andre;

Skepticism is good, but too much of anything is too much.

Irrelevant. Doesn't change anything to the truth

Anyhow, If you check around I'm sure you will find that there are several species of horses and antelopes well adapted to cold climates. In fact, there are still ape like creatures from tropical Africa that settled in the Arctic.

Of course. that's not the point. The point is that there are no grazers on an ice sheet of several 1000s feet height and we are looking for the missing ice sheets to add up to the isotope - ice volume hypothesis.

Edit, addition

There was no ice sheet on Finland either.

http://www.cosis.net/abstracts/EGU05/04737/EGU05-J-04737.pdf

 

[Xnn]

Andre;

I thought you were suggesting that horses and antelopes for some reason could not exist is the same lattitude as glaciation. If you have some other reason to doubt NH glaciation between 20 - 50ka being more extensive than the present, then perhaps you could explain it better, but I'd be skeptical of that.

 

[Andre]

Andre;

I thought you were suggesting that horses and antelopes for some reason could not exist is the same lattitude as glaciation. If you have some other reason to doubt NH glaciation between 20 - 50ka being more extensive than the present, then perhaps you could explain it better, but I'd be skeptical of that.

You're moving the goal posts again, forgetting to mention "much".

Years ago, ice sheet models were used to try and match the isotope balance of the Isotope stages. Fortunaltely there was little hard data on the extent of the ice sheets and Siberia was unassessable politically. So it was easy to project large ice sheets over there and balance the numbers.

In reality there was not a trace of ice over there in the period of interest as shown in the previous refs meaning that the numbers don't add up anymore.


Edit: There was not a lot of ice sheet on Finland and NW Russia neither:

http://www.cosis.net/abstracts/EGU05/04737/EGU05-J-04737.pdf

..Nine samples of bone and tooth enamel from woolly mammoth (Mammuthus primigenius)
remains found from Finland, Russian Karelia andWestern Russia were analysed...

All samples have been radiocarbon dated in previous studies (Ukkonen et al., 1999; Lõugas et al., 2002; Saarnisto & Lunkka, unpub.;M. Saarnisto, pers.comm. 2003; I. Demidov, pers.comm. 2003), and are of late Middle Weichselian to Late Weichselian age, ranging from > 45 800 to 18 700 cal yr BP.

 

[Xnn]

Andre;

The extent of NH glaciation between 20 to 50ka was much more extensive than it is now.

It wasn't a constant amount the entire period, as I'm sure it varied.
Also, I can't quantify how much greater it was, but it was clearly much more extensive than the present.

 

[baywax]

You're moving the goal posts again, forgetting to mention "much".

Years ago, ice sheet models were used to try and match the isotope balance of the Isotope stages. Fortunaltely there was little hard data on the extent of the ice sheets and Siberia was unassessable politically. So it was easy to project large ice sheets over there and balance the numbers.

In reality there was not a trace of ice over there in the period of interest as shown in the previous refs meaning that the numbers don't add up anymore.Edit: There was not a lot of ice sheet on Finland and NW Russia neither:

http://www.cosis.net/abstracts/EGU05/04737/EGU05-J-04737.pdf

Galapagos of the North (Haida Gwaii)

Apparently parts of these islands were spared the ravages of the last Ice Age. You can see that diversity appears to have continued here whereas elsewhere it was suppressed.

The fact they missed out on certain effects from the last ice age, coupled with their isolation from the Canadian mainland, has resulted in an abundance of organisms. Thirty-nine subspecies of endemic plants and animals have been recorded so far, including unique varieties of moss, fish, and the Haida Gwaii bear - a fine example of evolution in action. Stuck in an environment where small mammals were rare, this subspecies decided to snack instead on the shellfish that litter the islands' coastline. The result is the biggest black bear on Earth, with giant jaws perfectly adapted to prising open clams and mussels.

http://www.smh.com.au/news/canada/galapagos-of-the-north/2008/04/10/1207420567833.html

There is some evidence of human migration coming down from the Yukon Territories on an inland route, but the dates are inconclusive at this time... though one site was dated only by stratification as being around 13,000 bp. This would put it at the LGM. Perhaps a southern vacation trip for the Bluefish Cave people.

 

[Andre]

Andre;

The extent of NH glaciation between 20 to 50ka was much more extensive than it is now.

Would you have any direct evidence for that? Note that using the isotope stages is a begging the question fallacy, the same hypothesis is not proof for the hypothesis. So far we have only found areas which were not glaciated.

and

Andrea;

The Huybers paper explains that glaciers/ice caps are sensitive to insolation integrated over the duration of the summer. And integrated summer insolation is primarily controlled by obliquity and not precession, which is on a 40K yr cycle.
However, as the Earth cooled during the Pleistocene, the 40K cycle heat eventually wasn't always enough to triger glacial termination.

Sometimes it wasn't until the 2nd or 3rd cylces that the glacial sheets would be sufficiently melted. 80K and 120K averaged out to 100K.

So, there really is no pure 100K cycle. It just happens to be the average value over the last million years of 2 or 3 40K cycles.

That's exactly the problem as we just have found out that the ice did in fact retreat after the second Weichselian glaciation, yet this is not visible in the isotopes.

 

[Xnn]

Andre;

If you have a good paper about this isotope thing you are all concerned about, I can review it, but until then I won't comment on it.

However, there is plenty of evidence that the extent of glaciation during the last glacial maximum was much greater than the present. Consider the rise in sea level for starters.

130 meters of sea level is an awful lot of ice!

Could there have been a limited retreat between 50ka to 20ka?
Yes, but not to the same extent as the present.

 

[Andre]

yes that sea level rise, first of all this is after the Last Glacial Maximum of which I have no reason to challenge that for now; I'm challenging only the extend of the ice sheet before it. But still there is something strange with that sea level rise, especially that Melt Water Pulse 1A. let's dig up a very old thread here and copy paste (sorry links broken):

In another thread I murmured something about asymmetric climate problems at the end of the last ice age. Here, I’ll show three studies that form a big conflict together around a sudden sea level rise that is known as “Melt Water Pulse 1A”. ...

Clark et al (2004), http://www.geo.oregonstate.edu/people/faculty/clark_publications/Clarketal.-Science-2004.pdf. Science 21 May 2004: 1141-1144

In which it is shown that clear geologic evidence exists that the great melting at the end of the ice ages started 19,000 years ago, which is a bit odd since the ice cores of Antarctica did not start to show any warming before 17,300 years ago, whilst the Greenland Ice cores waited until some 14,600 years ago. So Clark et al contend:

The initiation of warming at 19,000 years B.P. at Atlantic and Antarctic sites (Fig. 3, D to F) records this expected ocean response to the 19-ky MWP. In particular, we note that warming occurred at Antarctic sites before any substantial rise in atmospheric CO2 (23) and despite a gradual decrease in austral summer insolation.

We have two remarkable things here that the warming began some 2000 years before the CO2 rose, which is held responsible for a large role in that warming and second, that it was Antarctica that warmed and hence started to melt. Let’s keep that in mind when we look at a second study about that Meltwater Pulse 1A.

Weaver A.J. et al (2003) http://www.geo.oregonstate.edu/people/faculty/clark_publications/weaveretal.-science-2003.pdf 14 March 2003 Vol 299 Science pp1710 - 1713

Meltwater pulse 1A (mwp-1A) was a prominent feature of the last deglaciation, which led to a sea-level rise of about 20 meters in less than 500 years. Concurrent with mwp-1A was the onset of the Bølling-Allerød interstadial event (14,600 years before the present), which marked the termination of the last glacial period. Previous studies have been unable to reconcile a warm Northern Hemisphere with mwp-1A originating from the Laurentide or Fennoscandian ice sheets. With the use of a climate model of intermediate complexity, we demonstrate that with mwp-1A originating from the Antarctic Ice Sheet, consistent with recent sea-level fingerprinting inferences…

That’s pretty clear. ...it’s also mentioned again that the warming in the south started as early as 19000 years ago. BTW this is not the only study that gives Meltwater Pulse 1A an Antarctic origin.

Also keep in mind that the current ice sheet of Greenland, central in the public interest, is good for a sea level rise of 7 meters. Apparently, Meltwater Pulse 1A was equivalent to the melting of almost three Greenland ice sheets within 500 years.

But now the third study:

Clark P.U. and Mix A.C (2002)http://www.geo.oregonstate.edu/people/faculty/clark_publications/clark&mix-qsr-2002.pdf, Quaternary Science Reviews 21 (2002) 1–7

We are interested in table 1 about the contribution of the several Ice sheets to the sea level rise. For Antarctica we see a series of 24,5 meters from the oldest studies to 14,0 meters in the more recent studies. Given the fact that there is hardly any tectonic post glacial rebound at Antarctica, that only land ice counts and that there is no room whatsoever to have 2-3 additional Greenland Ice sheets anywhere on the Antarctic continental shelf, 14 meters does seem to be quite a bit already. Now as the melting apparently started 19,000 years ago and lasted several thousand years as the end of the Ice age is marked at 11,600 years ago, you’d expect only millimetres per year from Antarctica but no, it was 20 meters in 500 years, meltwater pulse 1A.
...

As said although the links are broken, the refs are complete and it should be possible to retrieve. So what is MWP1A in reality and what is going on here?

 

[baywax]

yes that sea level rise, first of all this is after the Last Glacial Maximum of which I have no reason to challenge that, I challenge only the extend of the ice sheet before it. But still there is something strange with that, especially that Melt Water Pulse 1A, there something with that, let's dig up a very old thread here and copy paste (sorry links broken):
Links are broken but the refs are complete and it should be possible to retrieve. So what is MWP1A in reality and what is going on here.

I seem to remember a mention of the sea floor rising due to an unrelated (to glaciation) event... thus, giving the false appearance that the sea level had risen around that period. Do you remember what that was Andre?

 

[turbo]

I seem to remember a mention of the sea floor rising due to an unrelated (to glaciation) event... thus, giving the false appearance that the sea level had risen around that period. Do you remember what that was Andre?

I am not a climatologist, nor do I play one on TV. As a soils-tester/soils scientist back in the '70s (when I naively thought that I could chase seasonal construction jobs all over the state and make good money, I can assure you that during our last period of marine sedimentation (corresponding with the recession of the glaciers covering Maine) the oceans covered low elevations to a latitude of about 45 deg N. Clay and silt deposits pretty much lock in that event. When I was a kid, we were told that the glacial cap depressed the crust, and I have seen enough evidence of glaciation on fairly significant mountains (including the deposition of much earlier fossil-bearing sedimentary rocks at high elevations) to believe that this was true, though most of the fossil record may have been established before the Appalachian uplift event. Non-climatologist out.

 

[Xnn]

Historic sea level record over last million years.

Nothing within 50 meters of current levels between 20 to 50ka;
clearly impling much more estensive glaciation.

A slight rise around 30ka when the perihelion was in summer
and enough melt water pulses to keep everyone guessing!

 

[Mammo]

Historic sea level record over last million years.

Nothing within 50 meters of current levels between 20 to 50ka;
clearly impling much more estensive glaciation.

A slight rise around 30ka when the perihelion was in summer
and enough melt water pulses to keep everyone guessing!

I agree that sea levels show that glaciation was more extensive compared with today between 20 to 50 ka. But it is still possible that northern Siberia was warmer than today due to a stronger Gulf Stream bringing warm water into the Arctic basin. Hence a solution to the horses and antelopes, the 'Canadian Galapagos' and human dispersal conundrums. It all fits.

 

[Andre]

But we should be sure if we are looking at the real sea levels here. The graph is actually the result of modelling based on hypotheses suffering from several assumptions that may or may not be true. We can only be sure when the graph is supported by evidence, there is some evidence that the last 20,000 years is about sea level rise, although the impossible Meltwater Pulse 1A puts some question marks to it, however remember this post in the other thread, which focus in on the early period in b):

There are still more problems around the dating of the last interglacial, the Eemian aka Sangamonian.

http://www.sciencemag.org/cgi/content/abstract/283/5399/197

..The early (about 140,000 years ago) start of the penultimate deglaciation, well before the peak in insolation, is consistent with the Devils Hole chronology..

and
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V61-4NPG0G1-5&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=24ce14d831a1e24f41f6caa61725cd9d

...The age of the younger flowstone demonstrates that the early highstand occurred before 134.8 ± 2.0 ka, and uplift arguments suggest that the bioherms are unlikely to be older than 136 ka. These data are consistent with the notion that most of termination II (TII) sea-level rise had occurred before 135 ka; indeed they suggest sea-level at this time reached about 2–4 (± 4) m below present sea-level, 6–18 (± 4) m higher than previous estimates. This early highstand was itself punctuated by a rapid sea-level oscillation of > 10 m (as yet undated), and this oscillation, supported by new TII sea-level data from the Red Sea [Siddall, M., Bard, E., Rohling, E.J., Hemleben, C., 2006, Sea-level reversal during termination II, Geology, 34, 817–820.], probably occurred in about 1000 yr.

but also similar problems earlier http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VBC-4K717WK-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=f35a8571598ae887ad898cb5755cfc24

...But U–Th and δ18O data indicate the presence of an additional highstand which post-dates the expected end of MIS 7 (*) by up to 10 ka. This event is also seen in coral reconstructions of sea-level. It suggests that sea-level is not responding in any simple way to northern-hemisphere summer insolation,...

..Although the most extreme of these dates may not be reliable (based on the low-aragonite content of the sediment) the other three appear robust and suggest that full MIS 9 interglacial conditions were established at 343 ka. This is ≈8 ka prior to the date expected if this warm period were driven by northern-hemisphere summer insolation

(*) MIS= Maritime Isotope Stage, commonly used counted periods of general high and low isotope ratio's (δ¹⁸O) in the oceanic sediment cores, we are now in MIS1, MIS2 was the last glacial maximum.

So if there is a clear area where things do not add up, isn't this a reason to rethink basics?

 

[Mammo]

Mammo;

Hopefully, I can figure out how to include attachments here.

About 2.5 million years ago periodic ice ages began.
Originally, the warm periods were on 41,000 year cycles.
Over time, the warm periods degraded to 100,000 year cycles.

The Earth's orbit basically has 20,000, 41,000 and 100,000 year cyles to it.
There is not much difference between the 41,000 and 100,000 year cycles.
So, it has been a struggle to figure out why the Earth did the transition.
The latest that I've heard is that CO2 levels were just getting too low and the Earth appeared to be gradually slipping into a permanent ice age.

Here's a useful image and an good science article.

This is an interesting summary of the situation: http://www.moraymo.us/current_projects.php . The change from a 41,000 to 100,000 cycle appears to be quite abrupt. What is the mechanism for an abrupt permanent decrease in global CO2 levels?

But it's a bit different.

The big main eccentricity cycle are http://books.google.nl/books?id=s78sAPvQjN0C&pg=PA66&lpg=PA66&dq=eccentricity+cycle+413,000&source=bl&ots=P3XwkpkuWL&sig=h9GsEc4ZXmpxZ2UwQdycHfw8-3w&hl=en&sa=X&oi=book_result&resnum=9&ct=result . (413 ka and 100ka)

The former is stronger but does not show up at the Maritieme Isotope Stages, the latter is weaker but seems to dominate the cycles. I have never heard a satisfactory explanation for that.

There are more events that could be tied to the switch from the 41ka world to the 100ka world, the magnetic reversal from Matuyama to Brunhes chron (730 Ka ago). the latter being much more variable than the former and the Stilostomella extinction during the Mid Pleistocene.

Is it possible that the switch could be linked to the joining of the North and South American continents due to continental drift? This would imply that ocean current circulation is a pivotal parameter in glaciation cycles. An interesting article on the latest satellite measurements of continental drift is here: newscientist article

 

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This is an interesting summary of the situation: http://www.moraymo.us/current_projects.php. The change from a 41,000 to 100,000 cycle appears to be quite abrupt. What is the mechanism for an abrupt permanent decrease in global CO2 levels?

Is it possible that the switch could be linked to the joining of the North and South American continents due to continental drift? This would imply that ocean current circulation is a pivotal parameter in glaciation cycles. An interesting article on the latest satellite measurements of continental drift is here: newscientist article

I'm not so sure that CO2 levels dropped abruptly; rather they gradually lowered until the 41K cycles were no longer enough to trigger de-glaciation. Once that happened, the climate had to wait for something more than the normal 41K forcing.

I suspect it was a combiation of things that caused the cooling; the ithmus of Panama closing, Himilayians getting that much higher and proflieration of C4 plants.

The closing of the Panama Ithmus is the most difficult for me to understand. Indeed, I suspect nobody can really prove how that would work. The modeling of ocean currents is very poor. It occurs at roughly the right time, but coincidence does not prove causation.

However, for instance maybe somehow the ithmus shifted ocean currents enough to bring more rain to the Amazon or some other part of the world and that allowed enough additional plants to grow that they absorbed substiantlly more CO2. Or maybe the extra rain fell on the Himilayians where it weathered rocks and washed into the sea.