Happy Perihelion: Closest Approach to the Sun!

[Mammo]

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.

Okay, that makes sense, but what exactly is that 'something'?

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.

Now I've thought about it more, I suspect that the closing of the Panama Isthmus could be dated to around 2.5 million years ago and be responsible for the start of the age of glaciations. The additional current could be the tipping point needed for the Gulf Stream to reach the Arctic basin. It is not only summer melt temperatures which define glaciation but also the rate of snow accumulation. A stronger Gulf Stream would imply more precipitation for the landmasses of 65' N. Some areas would be warmer, such as northern Siberia, and some areas colder, such as North America, due to the extension of the icesheets. Is this too fanciful a notion?

 

[Xnn]

Mammo;

That is a good point. Wthout the Gulf Stream, there may not have been enough moisture in the Northern Hemisphere for ice sheets to grow. It could also have something to do with the Gulf of Mexico becoming much warmer than it would have been otherwise, and allowing it to be a source of moisture for the area of the Laurentide ice sheet.

 

[Mammo]

Mammo;

That is a good point. Wthout the Gulf Stream, there may not have been enough moisture in the Northern Hemisphere for ice sheets to grow.

Thanks for that. This side of the argument often seems neglected.

It could also have something to do with the Gulf of Mexico becoming much warmer than it would have been otherwise, and allowing it to be a source of moisture for the area of the Laurentide ice sheet.

A fair point, but you then have to explain the reason behind the warming of the Gulf of Mexico.

 

[Xnn]

The prevailing winds at the latitude of the Gulf are from the east and the surface waters tend to move westward.

With the Ithmus in place, it blocks surface waters from being blown into the Pacific, thus allowing the Gulf to warm more than it would otherwise.

 

[Mammo]

The prevailing winds at the latitude of the Gulf are from the east and the surface waters tend to move westward.

With the Ithmus in place, it blocks surface waters from being blown into the Pacific, thus allowing the Gulf to warm more than it would otherwise.

The warming effect due to frictional forces would, at first thought, be very minimal. The Wikipedia entry on the Panama Isthmus is quite enlightening:

"The Isthmus of Panama, also historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North and South America. It was formed some 3 million years ago during the Pliocene epoch."

"Scientists believe the formation of the Isthmus of Panama is one of the most important geologic events in the last 60 million years. Even though only a small sliver of land relative to the sizes of continents, the Isthmus of Panama had an enormous impact on Earth's climate and its environment. By shutting down the flow of water between the two oceans, the land bridge re-routed ocean currents in both the Atlantic and Pacific Oceans. Atlantic currents were forced northward, and eventually settled into a new current pattern that we call the Gulf Stream today. With warm Caribbean waters flowing toward the northeast Atlantic, the climate of northwestern Europe grew warmer. (Winters there would be as much as 10 °C colder in winter without the transport of heat from the Gulf Stream.) The Atlantic, no longer mingling with the Pacific, grew saltier. Each of these changes helped establish the global ocean circulation pattern in place today. In short, the Isthmus of Panama directly and indirectly influenced ocean and atmospheric circulation patterns, which regulated patterns of rainfall, which in turn sculpted landscapes.[1]

Evidence also suggests that the creation of this land mass and the subsequent, warm wet weather over northern Europe resulted in the formation of an Arctic ice cap and contributed to the current ice age."

 

[Xnn]

I did not mean to imply that frictional forces would warm the waters. Instead, that the prevailing winds generally tend to blow warmer equatorial waters from between Africa and S. America into the Gulf. Without a downwind exit, the Gulf tends to gather a lot of warm water.

I also didn't realize that the Atlantic was saltier than the Pacific.

 

[Mammo]

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.

Going back to an early post, I looked into the http://www.people.fas.harvard.edu/~phuybers/Doc/HuybersWunschNature2005.pdf and have now realized that this combining of obliquity cycles to explain the 100 kyr signal is just a theory. It is far from conclusive and does not dispute the possibility of an orbital eccentrcity component. It is only stating that the 41 kyr cycle is most definitely a major factor in the deglaciation cycles.

 

[baywax]

Coronal mass ejections during a solar maximum may explain the extreme nature of the Meltwater pulse occurring at the end of the LGM.

Paper:

Abstract

Hammer et al. (Climatic Change 35 (1997) 1) report the presence of regularly spaced acidity peaks (H+,F-,Cl-) in the Byrd Station, Antarctica ice core. The event has a duration of about one century and falls at the beginning of the deglacial warming. Volcanism appears to be an unlikely cause since the total acid deposition of this event was about 18 fold greater than the largest known volcanic eruption, and since volcanic eruptions are not known to recur with such regularity. We show that the recurrence period of these peaks averages to 11.5±2.4 years, which approximates the solar cycle period, and suggest that this feature may have an extraterrestrial origin. We propose that this material may mark a period of enhanced interstellar dust and gas influx modulated by the solar cycle. The presence of this material could have made the Sun more active and have been responsible for initiating the warming that ended the last ice age.

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6T-4F02GW3-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=525b790381836d913d8c819d3245c1cc

 

[Andre]

Going back to an early post, I looked into the http://www.people.fas.harvard.edu/~phuybers/Doc/HuybersWunschNature2005.pdf and have now realized that this combining of obliquity cycles to explain the 100 kyr signal is just a theory. It is far from conclusive and does not dispute the possibility of an orbital eccentrcity component. It is only stating that the 41 kyr cycle is most definitely a major factor in the deglaciation cycles.

Not even a theory, it's a hypothesis because it has not been tested. That's why I took some effort in the first posts of this thread to search for ice sheets in between glacial advances. So far nothing.

 

[Andre]

Coronal mass ejections during a solar maximum may explain the extreme nature of the Meltwater pulse occurring at the end of the LGM.

Paper:

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6T-4F02GW3-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=525b790381836d913d8c819d3245c1cc

Have you seen the complete paper? I miss the link with the meltwater pulses during the glacial transition, of which the largest (MWP1A) can be considered doubtfull, lacking a distinct source. https://www.physicsforums.com/showpost.php?p=2023624&postcount=28

 

[baywax]

Have you seen the complete paper? I miss the link with the meltwater pulses during the glacial transition, of which the largest (MWP1A) can be considered doubtfull, lacking a distinct source. https://www.physicsforums.com/showpost.php?p=2023624&postcount=28

Sorry, I haven't seen the whole paper... I'll try to dig it up.

Here it is Andre: Solar Cycle Variations in Ice Acidity at the End of the Last Ice Age: Possible Marker of a Climatically Significant Interstellar Dust Incursion

Full paper in PDF

http://arxiv.org/pdf/physics/0502019v1

 

[Andre]

Thanks Baywax, not surprising that the solar cycles are reflected in the ice cores. The 15,8 Kya Electrical Conductivity spike is food for thought. As far as I recall, there are no other events known at that time while Melt Water Pulse 1A is dated around 14,5 Kya at the onset of the Bolling event.

 

[Mammo]

Not even a theory, it's a hypothesis because it has not been tested. That's why I took some effort in the first posts of this thread to search for ice sheets in between glacial advances. So far nothing.

I feel a bit foolish by being taken in by Xnn's initial confidence. The Wikipedia Milankovitch Cycles entry is very informative. I can't believe that I hadn't seen it before.

Sorry, I haven't seen the whole paper... I'll try to dig it up.

Here it is Andre: Solar Cycle Variations in Ice Acidity at the End of the Last Ice Age: Possible Marker of a Climatically Significant Interstellar Dust Incursion

Full paper in PDF

http://arxiv.org/pdf/physics/0502019v1

It's an interesting paper in general. I've only just printed it out and intend to go through it in detail. Nice find.

 

[Andre]

I feel a bit foolish by being taken in by Xnn's initial confidence. The Wikipedia Milankovitch Cycles entry is very informative. I can't believe that I hadn't seen it before.

Reason enough to do the "auditting", don't you think?

 

[Xnn]

Hey; now what am I being accused of?

The main point of the Huybers paper is that glaciers are primarily sensitive to insolation integrated over the duration of the summer. The maximum solar intensity or the duration of the summer is not as important. Eccentricity plays a part in the integrations, but has a minor role compared to obliquity. So, when ever anyone tries to correlate insolation to climate, keep in mind that it should be an integrated value and not just the peak summer value.

To fully explain these climatic cycles there will have to be advances in understanding the behavior of glaciers to changes in solar isolation, temperature, humidity as well as how greenhouse gases rise and fall and at least a dozen other things. In short it becomes more a problem of modeling the Earth's entire climate as opposed to looking for simple one to one correlations.

For example, it is commonly understood that the albedo of freshly fallen snow is extremely high; maybe 0.95. Over time, it lowers to about 0.80. As snow warms it drops to 0.4 and when melt ponds begin to form it can get as low as 0.1. These are huge differences, and guess what: They are not well understood or modeled. The same can be said of ocean currents and variable climate patterns like ENSO.

On top of that we have all types of seemingly random events that can also make huge short term differences. Volcanic eruptions and comets for example.

 

[baywax]

Thanks Baywax, not surprising that the solar cycles are reflected in the ice cores. The 15,8 Kya Electrical Conductivity spike is food for thought. As far as I recall, there are no other events known at that time while Melt Water Pulse 1A is dated around 14,5 Kya at the onset of the Bolling event.

Apparently I can't cut and paste from the document right now but somewhere in the middle of the paper there are references to why cosmic dust would first cool then cause a warming enough to de-glaciate. Its a pretty comprehensive paper. It just sounds kind of "loony" when he goes on about "galactic rays" etc... but, hey, we are in a galaxy here!

 

[Xnn]

Its a pretty comprehensive paper. It just sounds kind of "loony" when he goes on about "galactic rays" etc... but, hey, we are in a galaxy here!

I agree!

There have been at least 20 glaciation and de-glaciations over the past few million years.
They tend to happen at a periodicity of 40k years, until more recently when they occurred less frequently. These have been correlated for the most part to regular changes in Earth's orbit.

So, while there may have been a galactic ray occurance at some time in the past, it is difficult to see how or why galactic rays could explain all the other glaciations and de-glaciations.

 

[Andre]

I agree!

There have been at least 20 glaciation and de-glaciations over the past few million years.
They tend to happen at a periodicity of 40k years, until more recently when they occurred less frequently. These have been correlated for the most part to regular changes in Earth's orbit.

Have they? Can we have a look at that. Does it also explain the MIS-6 termination (Saalian/Illenoian) chronology problems?

 

[Xnn]

Have they? Can we have a look at that. Does it also explain the MIS-6 termination (Saalian/Illenoian) chronology problems?

Sure; just take a look at Figure 3 of the following link:

http://www.people.fas.harvard.edu/~phuybers/Doc/HuybersTziperman_Paleoceanography2008.pdf

 

[baywax]

So, while there may have been a galactic ray occurance at some time in the past, it is difficult to see how or why galactic rays could explain all the other glaciations and de-glaciations.

Its possible there is a corresponding cycle to the "galactic ray volleys" that matches the glaciation and deglaciation.

I've pulled a snippet off the PDF but the attachment gods don't work on sunday. It is where the "galactic ray volley" is mentioned in the paper. I'll try later. Its around page 8.

 

[Andre]

Sure; just take a look at Figure 3 of the following link:

http://www.people.fas.harvard.edu/~phuybers/Doc/HuybersTziperman_Paleoceanography2008.pdf

Exactly, the stubborn reality as demonstrated earlier does not fit in the hypothesis pattern, so it is ignored and replaced with models which can make elephants fly.

Without a clear explanation why the conflicts noted by Esat et al 1999, Henderson et al 2006, Andrews et al 2007 and others are cathegorically ignored, there isn't much of a case, is there?

 

[Xnn]

... there isn't much of a case, is there?

Ahhh, just the opposite!

All the more reason to write grant requests and commission more studies to resolve yet another problem with consistent dating.

 

[Andre]

Ahhh, just the opposite!

All the more reason to write grant requests and commission more studies to resolve yet another problem with consistent dating.

You're commercializing science.

In the old days it would be a Popperian falsification. Failed hypothesis, end of story.

 

[Xnn]

Ahh Andre;

Such drama.

Realistically, there have got to be hundreds of problems with inconsistent dating of all the various geological measurements. Nothing is perfect and people do make mistakes.

Some are bigger deals than others. Who is to say which has a chance of shaking the fundamentals of science or is just a case of somebody making an error.

That is why there are reviews of grant request. It if is important enough, then somebody will be able to easily justify a grant. If not, then maybe someday, somebody will figure out exactly where the error is. The key is that there are priorities.

Just because somebody thinks they found an error in somebody else's work is no gurantee that there is something wrong with the funadamentals. It could just be a lousy field data/study/paper/journal.

So, if it is possible that there is a real problem, then a grant will be requested, a study will be done, and if it gets past peer reviews of a reputable science journal then people will someday say either:

1. Somebody corrected a previous mistake that got past peer review.

Or;

2. Hey, there really is something fundamentally wrong with how everybody was thinking.

However, it would be wrong to automatically jump to the conclusion that all discrepancies are indications that there are wide spread fundamental misunderstandings.

 

[Andre]

Ahh Andre;
So, if it is possible that there is a real problem, then a grant will be requested, a study will be done, and if it gets past peer reviews of a reputable science journal then people will someday say either:

1. Somebody corrected a previous mistake that got past peer review.

Or;

2. Hey, there really is something fundamentally wrong with how everybody was thinking.

However, it would be wrong to automatically jump to the conclusion that all discrepancies are indications that there are wide spread fundamental misunderstandings.

So far we have seen discrepancys in the sea levels at the last two terminations, a prelimilary highstand well in MIS 6 instead of the end of it. Then there is the impossible Meltwater Pulse A1 having no source. Next, we have seen that the isotope - ice volume hypothesis does not add up.

Then there is the preliminary NH warming prior to the Bolling event, challenging the Greenland istope thermometer and the other isotope proxies (Ammersee and several speleothems). and I didn't say that we are done, yet

So what you do think it's going to be?

 

[Xnn]

So, what do you think it's going to be?

Lots and lots of grant requests!

I mean if these are legitimate discrepancies (and I'm not enough of an expert to say if they are or are not), then it ought to be possible to get some money to figure them out. Of course, they won't give the money to anybody. But a person with the right credentials ought to able to. Wether the answer will be #1 or #2, it is not for me to say.



BTW;

This thread has gone a long way off topic, which was orignally about the Perihelion.
If anybody wishes to discuss the perihelion, then please feel free to add to this thread. However, if it is another topic, then please start a new thread.

Thanks,
Xnn