CO2 Variance in the Atmosphere

[Saul]

There is an unexplained mystery as to why atmosphere CO2 levels varies long term (geologically) and short term (glacial/interglacial cycle.)

Contrary to what is repeated in many blogs the glacial/interglacial cycle changes of about 90ppm to 100 ppm is not due to colder oceans being able to hold more CO2.

Simple back of the envelop analysis considering the change of solubility of CO2 in water with temperature, the maximum cooling of the ocean possible (The limit of ocean cooling is freezing the entire ocean.) and the increase in CO2 due to the reduction in the area of the planet covered by plants during the glacial period (In addition during the glacial phase, many plants die due to extremely low CO2, tropical forest are converted to grasslands and vast regions of the planet are covered by ice sheets which increases atmospheric CO2 by roughly the same amount as cooling oceans.), indicates the absolute maximum explainable due to planet cooling during the glacial period 6.5 ppm. The remaining 80 ppm to 90 ppm is drop in CO2 has no explanation.

Also puzzling is C12 significantly increases during the glacial period.

Possibly the answer to this puzzle would also explain why CO2 levels have been dropping on the planet over the last 25 million years. CO2 prior to anthropic changes, were at the lowest level in 500 million years.

Has anyone seen any papers that try to explain the long term drop in CO2?

This paper explains the mystery and proves a hypothesis that wind blown dust during the glacial period (The planet is drier when it is colder. Many plants die as a result of the low CO2 during the glacial period so desertification increases.) makes the oceans more productive and that more productive ocean (algae) reduces CO2.

The paper I provide a link to was published in 2000. A more recent paper shows the CO2 changes due not correlate with wind blown dust that increase by a factor of roughly 10 times during the glacial periods. I also have a very recent power point presentation that notes this problem is close to becoming a paradox.

http://www.up.ethz.ch/education/biogeochem_cycles/reading_list/sigman_nat_00.pdf

Glacial/interglacial variations in atmospheric carbon dioxide by Daniel M. Sigman & Edward A. Boyle

Twenty years ago, measurements on ice cores showed that the concentration of carbon dioxide in the atmosphere was lower during ice ages than it is today. As yet, there is no broadly accepted explanation for this difference. Current investigations focus on the ocean's `biological pump', the sequestration of carbon in the ocean interior by the rain of organic carbon out of the surface ocean, and its effect on the burial of calcium carbonate in marine sediments. Some researchers surmise that the whole-ocean reservoir of algal nutrients was larger during glacial times, strengthening the biological pump at low latitudes, where these nutrients are currently limiting. Others propose that the biological pump was more efficient during glacial times because of more complete utilization of nutrients at high latitudes, where much of the nutrient supply currently goes unused. We present a version of the latter hypothesis that focuses on the open ocean surrounding Antarctica, involving both the biology and physics of that region.

An opposing effect on atmospheric CO2 to that of glacial/ interglacial temperature change is provided by the increased salinity of the glacial ocean, due to the storage of fresh water on land in extensive Northern Hemisphere ice sheets. Based on the approximately 120m depression of sea level during the last ice age18, the whole ocean was about 3% saltier than it is today. All else being constant, this increase would have reduced the solubility of CO2 in sea water and raised atmospheric CO2 by 6.5 p.p.m.v. Taking the estimated temperature and salinity effects together, we would expect the atmospheric CO2 concentration of the ice age world to have been 23.5 p.p.m.v. lower. Folding in the effect of a 500 Pg C transfer from the continents to the ocean/atmosphere system, we are left with an 8.5 p.p.m.v. decrease in CO2 (Table 1). There are uncertainties in each of these effects, but it seems that most of the 80±100 p.p.m.v. CO2 change across the last glacial/ interglacial transition must be explained by other processes. We must move on to the more complex aspects of the ocean carbon cycle.

 

[sylas]

There is an unexplained mystery as to why atmosphere CO2 levels varies long term (geologically) and short term (glacial/interglacial cycle.)

I agree. This is an open research question, and we don't know all the details of how the carbon cycle works to resolve it.

Contrary to what is repeated in many blogs the glacial/interglacial cycle changes of about 90ppm to 100 ppm is not due to colder oceans being able to hold more CO2.

It's true enough that the magnitude of change in atmospheric CO2 is large, and that there is mostly like more involved that changes in solubility. Merely saying it is not due to colder oceans, however, is inadequate. Colder oceans do certainly contribute, and your own reference confirms it. The issue is rather; how much? And what else is going on to make up the difference?

Your reference proposes a fairly significant 30ppm contribution from increased solubility of CO₂ in colder oceans. That is large enough to be an important part of the equation, and even that might be an underestimate. But it's still not enough, and what is worse, the paper identities other effects, not directly from temperature, which may work in reverse so as to mask a large part of the draw down into colder oceans.

Simple back of the envelop analysis considering the change of solubility of CO2 in water with temperature, the maximum cooling of the ocean possible (The limit of ocean cooling is freezing the entire ocean.) and the increase in CO2 due to the reduction in the area of the planet covered by plants during the glacial period (In addition during the glacial phase, many plants die due to extremely low CO2, tropical forest are converted to grasslands and vast regions of the planet are covered by ice sheets which increases atmospheric CO2 by roughly the same amount as cooling oceans.), indicates the absolute maximum explainable due to planet cooling during the glacial period 6.5 ppm. The remaining 80 ppm to 90 ppm is drop in CO2 has no explanation.

As a minor correction, the number you want from your reference is 8.5, not 6.5. Your reference is:

• Sigman, D.M., and Boyle, E.A. (2000) http://www.up.ethz.ch/education/biogeochem_cycles/reading_list/sigman_nat_00.pdf , in Nature, Vol 407, 19 Oct 2000, pp 859-869.

The estimate is carried through on page 861, as follows:

• Based on a sea level drop of 120m, they estimate an increase in salinity of 3%. I think this must be based on total salt content with reduced volume; it's what I get using average ocean depth, which is 3790m. All else being constant (i.e.; no temperature change) the author states this would RAISE atmospheric CO₂ by 6.5ppm, though reduced solubility.
• As for the temperature effect, the authors cite a 30ppm decrease in atmospheric CO₂ from increased solubility. The discussion, however, notes explicitly that this is using a simple ocean box model, called CYCOPS, which might be underestimating the temperature sensitivity. They merely note that this is subject to debate. It's not back of the envelope stuff.
• The author ALSO takes into account a 500 Pg decrease in terrestrial CO₂, corresponding to another 15ppm transferred INTO the atmosphere. I got a bit lost with that calculation.
• All told, with +6.5 (salinity) -30 (temperature) +15 (terrestrial) the author concludes 8.5ppm drop in atmospheric CO₂.

I'm not an expert, and I think a lot of debate on this subject goes wrong because people overestimate their own knowledge. So I try to be cautious and realistic about what I've learned so far. And this is not a calculation I'm in a good position to defend as authoritative.

So I give it as a question; not a claim: how did he get such a large figure for the terrestrial to atmosphere transfer? He speaks of a 500Pg loss of terrestrial carbon, and that would correspond to about 250ppm if all into the atmosphere. With 15ppm change, he's giving some 6% of the decrease into the atmosphere. But the atmosphere is less than 1.5% of the total ocean/land reservoir, by his own figure 1. I may have mixed up my numbers here, but this sounds like way too much into the atmosphere. There is some discussion in the paper, and I didn't follow it too well. My back of the envelope hugely simplistic estimate, dividing up the 500 Pg proportionally between reservoirs, suggests a bit less than 4ppm gain from this effect; not 15. That raises the net drop from 8.5 to nearly 20ppm.

Similarly, it seems at least possible to me that receding oceans may actually end up depositing some of their salt load, and that increasing salinity may also make it easier for the ocean to deposit salt. If there's an equilibrium salt cycle (I'm guessing!) then the simple volume based calculation is going to over estimate salinity, and the salinity effect may be less than 6.5.

So any of his three estimated contributions could be a bit off. By and large, however, I agree that there's more going on, not taken into account in the simple +6.5 -30 +15 equation, even if we adjust them a bit. Any way you cut it, we don't know where all the carbon went. There are some speculative suggestions in the paper – and thanks for the reference. It's a good one to go into my collection.

Whatever else is contributing to the CO₂ drop, it is likely something to do with changes that take place in an ice age. Note the direction of causality here. Something is driving CO₂ levels. And we know only a part of what is involved.

Possibly the answer to this puzzle would also explain why CO2 levels have been dropping on the planet over the last 25 million years. CO2 prior to anthropic changes, were at the lowest level in 500 million years.

Has anyone seen any papers that try to explain the long term drop in CO2?

On very long time scales like this, it is bound to be involving the small fluxes of carbon into and out of geological reserves. That is, it's no longer just a case of ocean, atmosphere and biosphere. On long time spans, weathering and geological deposition become the main factors. There's quite a lot on this in the literature, and in the other thread I cited for you a good review article:

• Bergman, N.H. et al (2004) COPSE: A new model of biogeochemical cycling over Phanerozoic time, in American Journal of Science, Vol. 304, May 2004, P.397-437; doi:10.2475/ajs.304.5.397

That's just a start; you'll need to start following the references back from there. If you want to explain the drop, rather than merely measure it, then you want to look for papers that are model based rather than proxy based. The GEOCARB work is one of the most important references, I suspect.

Interesting stuff. Thanks -- Sylas

 

[Xnn]

Has anyone seen any papers that try to explain the long term drop in CO2?

Can't say I've seen a paper, but my understanding is that C4 plants evolved between 32 to 25 Ma.

C4 plants grow very fast, are more efficient at carbon fixation and are drought resistant.
Example include sugarcane, maize, sorghum and switchgrass.

Not sure if they are the primary cause, but suspect they are at least part of it.


http://www.eurekalert.org/pub_releases/2007-12/cp-alb122007.php

 

[Skyhunter]

Can't say I've seen a paper, but my understanding is that C4 plants evolved between 32 to 25 Ma.

C4 plants grow very fast, are more efficient at carbon fixiation and are drought resistant.
Example include sugarcane, maize, sorghum and switchgrass.

Not sure if they are the primary cause, but suspect they are at least part of it.


http://www.eurekalert.org/pub_releases/2007-12/cp-alb122007.php

C4 plants absorb more ¹³C where C3 plants have a preference for ¹²C.

¹²C would be expected to increase during glaciation since there are fewer C3 plants to absorb it

 

[Saul]

I have been looking at the formation of the planet's atmosphere as well as long term changes in CO2.

There is evidence of massive increases in CO2 from CH4 injection. The injected carbon is low in C13. (Curiously "natural gas" is also low in C13.) The injection rate is sustained for tens of thousands of years.

If you refer to my comments in Sylas' thread, I present evidence that CO2 saturates such that additional CO2 injected into the planet's atmosphere has less and less affect. This temperature increase can be explained by a steady release of CH4.

If you look at the spectrual analysis the absorption frequency of CH4 falls in a region that is currently transmitted out into space. A steady massive release of CH4 will cause the planetary temperature increase noted in this paper. CO2 will not.

Comment: Has anyone in the forum looked at the problem of how to explain the formation of the Earth's atmosphere and oceans?

Now the question is where is the source for the massive long term release of CH4?

An Ancient Carbon Mystery, Mark Pagani, Ken Caldeira, David Archer, James C. Zachoshttp://earth.geology.yale.edu/~mp364/data/2006Pagani.Science.pdf

Temperature records from the tropics to the poles indicate that at the start of the PETM, global temperatures increased by at least 5°C in less than 10,000 years (2). The rise in surface temperature was associated with changes in the global hydrological cycle (3) and a large decrease in the 13C/12C ratio of marine (4) and terrestrial carbonates (5) and of organic carbon (3). This carbon isotopic excursion indicates that changes in the global carbon cycle were linked to global warming.

Temperature records from the tropics to the poles indicate that at the start of the PETM, global temperatures increased by at least 5°C in less than 10,000 years (2). The rise in surface temperature was associated with changes in the global hydrological cycle (3) and a large decrease in the 13C/12C ratio of marine (4) and terrestrial carbonates (5) and of organic carbon (3). This carbon isotopic excursion indicates that changes in the global carbon cycle were linked to global warming.

Sustaining this concentration for tens of thousands of years implies partial equilibration with the carbonate system in the ocean, indicating a total release of 5400 to 112,000 PgC (see the second figure), with 3900 to 57,000 PgC of released carbon residing in the ocean (and with additional carbon supplied by the dissolution of carbonates). The extraordinary magnitude of these estimates is evident when compared against the 5000 PgC estimated for conventional fossil fuel resources available today.

 

[sylas]

If you refer to my comments in Sylas' thread, I present evidence that CO2 saturates such that additional CO2 injected into the planet's atmosphere has less and less affect. […]

I can't let a claim like that pass without comment. Your comments on saturation in the other thread ([post=2165276]msg #2[/post] and [post=2165577]msg #4[/post]) give no evidence; only a claim, or a "belief" that such evidence exists. (You have given evidence relating to other matters, of course.)

Your definition of the term "saturation" was non-standard. You originally proposed that it means no further temperature impact from additional CO₂. I explained in [post=2165483]msg #3[/post] of the other thread that it actually refers to absorption of light at a given frequency. The atmosphere is "saturated" at a given frequency if it is opaque, so that all the light at that frequency is absorbed.

The impact of a greenhouse gas (not only CO₂) is largely from increased absorption in the wings of a saturated band of the spectrum. Therefore the atmosphere is NOT saturated by your usage, and by conventional usage: increasing concentrations of CO₂ will increase the width of the saturated band. This is basic physics.

The reduced effect of CO₂ as atmospheric concentration increases is because the impact is logarithmic. This was explicit from my very first post in the other thread. The logarithmic relation holds for CH₄ as much as for CO₂. As concentrations of a greenhouse gas increase, you need larger and larger absolute additions for the same impact. The impact of additional gas is roughly proportional to the factor by which concentrations increase, not the absolute amount added.

We've made a fair bit of progress in the other thread, and some has been quite interesting. The discussion has moved on, with an implicit shared recognition of the underlying forcing from increased absorption. We're now looking at "sensitivity", or how much impact there is from forcing. That has nothing to do with "saturation". Climate sensitivity determines response to ANY forcing; solar, greenhouse, CO₂, CH₄, albedo, anything at all. It's a crucial part of the paper Saul has cited.

OK… back to this thread, paleoclimate, and the carbon cycle. The material above is relevant background, so keep it in mind. Continuing the quoted extract:

[…] This temperature increase can be explained by a steady release of CH4.

If you look at the spectrual analysis the absorption frequency of CH4 falls in a region that is currently transmitted out into space. A steady massive release of CH4 will cause the planetary temperature increase noted in this paper. CO2 will not.

The first part of this is fine. CH₄ does have a very strong warming impact, because atmospheric concentrations are so low. Even a small addition is a large proportional increase. The important absorption for CH₄ is around 8 microns, and this band is far from being saturated.

CH₄ is measured in parts per billion (ppb). CO₂ is measured in parts per million (ppm). Even though the absolute increase of CO₂ in the modern era has been about 100 times greater than the absolute CH₄ increase, the actual forcing impact is only about 3 times greater.

Your final three word claim on CO₂ is wrong, and conflicts with elementary physics as explained in the other thread. The impact of CO₂ is easily the largest greenhouse forcing in the modern era.

So… what about the notion that CH₄ might work for explaining large temperature changes in prehistory. Moving on…

Pagani et al (2006): An Ancient Carbon Mystery

Now the question is where is the source for the massive long term release of CH4?

An Ancient Carbon Mystery, Mark Pagani, Ken Caldeira, David Archer, James C. Zachos

http://earth.geology.yale.edu/~mp364/data/2006Pagani.Science.pdf

This is a well known and widely cited paper. Just for interest, one of the authors, David Archer, is a professor of geophysical sciences at the University of Chicago. He's the guy who provides the http://geosci.uchicago.edu/~archer/cgimodels/radiation.html I have been using to try and explain about saturation in the other thread. You can use it to explore the impact of CH₄ concentrations. Put the "sensor altitude" at about 15 to 20km (around the tropopause) looking down, and then fool around with CH₄ settings. Watch the changes in magnitude of outgoing radiation at the tropopause to get the approximate forcing.

Pagani et al addresses the PETM -- "Paleocene-Eocene Thermal Maximum". This strange and not yet well understood event occurred some 55 million years ago, and lasted about 170,000 years (a little bit longer than the most recent ice age, or "glacial"). In the PETM, temperatures increased by something like 5 degrees in less than 10,000 years. That's fast by geological standards. Explaining this is a difficulty.

The obvious explanation is a greenhouse effect from CO₂, given the observed change in carbon isotopes that Saul mentions. The abstract of this paper is brief and to the point:

Sudden global warming 55 million years ago provides evidence for high climate sensitivity to atmospheric CO₂, but the source of the carbon remains enigmatic.

-- Abstract, Pagani et al (2006) in Science, Vol 314, pp1556-1557​

Saul is asking the wrong question. It's not… where did the CH₄ come from? The question he should be asking is: how come these guys didn't think of the CH₄ explanation?

The answer is explicit in the paper, and implicit in Saul's own post. Saul himself says: "There is evidence of massive increases in CO2 from CH4 injection.". That's right. Adding CH₄ leads to higher CO₂ concentrations. Pagani et al explain why:

According to one hypothesis, the PETM was caused by the release of ~2000 PgC from the destabilization of methane hydrates (which would subsequently oxidize to form CO₂).

-- Pagani et. al. (2006) bottom of page 1556​

CH₄ is very reactive. It has a short atmospheric lifetime, of around 8 to 12 years. Hence adding large amounts of CH₄ to the atmosphere leads rapidly to an increase in CO₂. This reaction series is well known, and so the brief aside in the paper is sufficient to make the link between destabilized methane hydrates and increased CO₂.

Given that the temperature rise in the PETM was over 10,000 years, and the whole event lasted 170,000 years, CH₄ is not a credible basis for driving the impact. It can't last long enough. It can, however, be the source of a sustained CO₂ rise, and this is the reason for considering methane hydrates.

None of Saul's extracts from the paper back up his proposal for methane being the driver. They all refer to the problem of getting enough carbon into the atmosphere. Saul puts special bold emphasis on his third extract from the paper, but the implications deal with chemical equilibriation implications, which are the basis for rejecting a sustained high level of methane.

Rather than quote long extracts, I'll summarize the argument as given by Pagani et. al.

1. Estimates of atmospheric CO₂ before the PETM range from 600 to 2800ppm. (i.e. lots of uncertainty is acknowledged!)
2. Climate sensitivity is between 1.5 and 4.5 C per 2xCO₂. This is precisely the range I have been giving in the other thread, by the way.
3. The temperature increase is 5C. The factor increase is thus between 2^5/1.5 and 2^5/4.5. The smallest absolute increase would be from a 600ppm starting point, by a factor of 2.16 up to about 1300ppm, and the largest would be from a 2800ppm starting point by a factor of 10.08 up to about 28200ppm. 1ppm works out to 2.15 Pg of carbon, and so the total increase in carbon in the atmosphere ranges from about 1500 Pg to 55000 Pg. The full calculation is obvious; the paper only quotes the result.
4. (A minor aside. I bet they made a typo. There's a mention of 750ppm in the low bound calculation, which should probably be 700ppm. It's an intermediate value on the way to the 1500 Pg low bound on atmospheric carbon, and my working of the numbers from the same starting point to the same ending point suggests that 700 is the proper intermediate. 700*2.15 = 1505. The end result and the conclusions are unaffected.)
5. Immediately after this is the extract that Saul highlighted. Any increase in atmospheric carbon involves requires partial equilibration with carbon in the ocean, and a correspondingly larger amount of carbon into the oceans. The total amount of carbon required rises to a range of 5400 Pg to 112000 Pg.

A crucial number in this is the sensitivity. To get the low end estimate of carbon, you have to assume a high value of climate sensitivity. The conclusion of the paper, in the second last paragraph is as follows:

Thus, the PETM either resulted from an enormous input of CO₂ that currently defies a mechanistic explanation, or climate sensitivity to CO₂ was extremely high.

-- Pagani et al. (2006), second last paragraph.​

If Saul would like to argue that methane is a major climate driver, he's got the wrong peer reviewed source for doing it. This source uses carbon dioxide as the climate driver. So also does the cited reference first proposing methane hydrates for PETM, which is research by http://www3.bio.uu.nl/palaeo/people/Appy/index.html .

Methane in the Quaternary period, and in the industrial era

There are changes in CH₄ concentration in Earth's atmosphere over time. In the Quaternary, where they can be measured from ice cores, it ranges from about 400 to 700 ppb, and has a strong positive correlation with CO₂ and with temperature, as we should expect. This is over the cycles of ice ages (glaciations) occurring in the last 1.8 million years or so.

At these concentrations, the CO₂ forcing is much larger than the CH₄ forcing.

Since the industrial era, CH₄ concentrations have soared to 1700ppb, and this makes a substantial part of the anthropogenic greenhouse impact, almost 1/3 as much as the main CO₂ impact. This is also one of the ways the anthropogenic impact can be most effectively reduced, because as methane emissions drop, the atmospheric concentration will fall rapidly by the natural removal of CH₄ from the atmosphere.

Cheers -- sylas

 

[Xnn]

(Curiously "natural gas" is also low in C13.)

Comment: Has anyone in the forum looked at the problem of how to explain the formation of the Earth's atmosphere and oceans?

Now the question is where is the source for the massive long term release of CH4?

As I understand it, plants tend to deplete C13 when they form lipids, from which petroleum is derived. Not sure how natural gas is formed, but if it is from fractination of petroleum, then it'd make sense that natural gas is depleted in C13.

The current theory on the source of CH4 are methane clathrates in the ocean. Fortunately, these are mostly in deep cold water and are fairly stable. There is some concern that as polar waters warm there could be additional methane releases, but so far that doesn't not appear to be a significant factor.

Formation/evolution of the oceans and atmosphere is fascinating. Originally, the atmosphere was mostly water, CO2 and sulfur gas. Then it rained, and green oceans formed. Took a billion years or so to precepitate out the iron and get a blue sky. Likewise, to precepitate out the CO2 into carbonates. Then plant life eliminated almost all CO2 and the oceans almost totally froze. It wasn't until after the big thaw, that free oxygen existed and the cambria explosion occured. Nitrogen has steadily accumulated over history as it is inert.

 

[Saul]

Let’s set aside the CO2 does or does not saturate question and try to explain why CO2 levels in the atmosphere vary through time.

As CO2 is removed from the earth’s atmosphere by natural processes there needs to be a constant source to replenish the carbon that is removed to the mantel.

Let’s flash back to the early atmosphere and the paradoxes associated with explaining the observations.

Carbon is roughly 200 times more concentrated on the earth’s crust than it is in basement rocks. One theory to explain that finding is that the early Earth had an atmosphere which was roughly 80 times denser than its is currently (about the same as Venus which has a surface pressure of 90 atmospheres). This massive carbon dioxide atmosphere then precipitated out on to the crust. Plate tectonics and volcanic activity then releases carbon back in the atmosphere.

The fact that the Earth has a very low abundance of the heavy noble gases is a paradox for the all at once CO2 theory. As there is no mechanism to remove heavy noble gases from the earth’s atmosphere, if the early atmosphere was 80 times denser (80 atmospheres) than the current atmosphere there should be orders of magnitude more heavy noble gases in the current atmosphere.

Another issue with the all at once CO2 theory is that the sediment record (over the last 2 billion years) shows a steady deposit of carbonates as if the CO2 comes from a new source and is then deposited on the earth’s surface after reactions in the earth’s atmosphere and oceans. The source for the carbon appears to be CH4 which would also explain geological evidence for gradual increasing ocean level. (The oceans are currently saturated with CH4 and there is no explanation as to source.)

The continuous CH4 source hypothesis is supported by the C13/C12 ratio found in carbonate sediments. As plants preferentially use C12 the atmosphere would if the CO2 was recycled, gradually increase in C13 content, which when deposited in carbonates would create an increase in the C13 to C12 ratio as one moves up the carbonate deposit from deposits 500 million years ago to present.

That is not the case. The C13/C12 ratio remains roughly the same expect for occasionally periods when there is an abrupt increase in reduction in C13.

 

[Xnn]

The heavier noble gases (Xenon for example) at not totally inert. They have Van Der Wall forces and there are indications that they can bond with oxygen as well. See the following link for a possible explanation.

http://www.sciencemag.org/cgi/content/abstract/310/5751/1174

Not too sure about CH4 being constant in the oceans. Thought the PETM purged most of it and that it was gradually building up since then. However, if the oceans warm significantly, then CH4 could be released.

 

[sylas]

The heavier noble gases (Xenon for example) at not totally inert. They have Van Der Wall forces and there are indications that they can bond with oxygen as well. See the following link for a possible explanation.

http://www.sciencemag.org/cgi/content/abstract/310/5751/1174

That's interesting! Thanks very much... I had not known that the heavy noble gases can make co-valent bonds. And on reading a bit further, I even find that physicsforums has addressed such bonds before: thread [thread=142490]Coordinate Covalent Bonds[/thread].

Man, I love this forum.

Not too sure about CH4 being constant in the oceans. Thought the PETM purged most of it and that it was gradually building up since then. However, if the oceans warm significantly, then CH4 could be released.

What Saul is referring to, I think, is that the upper ocean seems to be saturated with methane. That would make it implausible to be building up since PETM; it implies a source hard at work over much shorter time spans. Here's a paper which might help on the source of so much methane in the upper ocean:

Karl, D. et al. (2008) Aerobic production of methane in the sea, in Nature Geoscience 1, 473 - 478 (2008)

Karl and colleagues became interested in the "methane enigma" and why the surface ocean was loaded with methane, well above levels found in the atmosphere.

They found a possible solution in the compound methylphosphonate, an unusual organic compound discovered in the 1960s.

-- from report at physorg.com​

Here's what I don't understand. Saul says:

The fact that the Earth has a very low abundance of the heavy noble gases is a paradox for the all at once CO2 theory.

What does CO2 have to do with the low abundance of heavy noble gases?

Cheers -- Sylas

 

[Saul]

That's interesting! Thanks very much... I had not known that the heavy noble gases can make co-valent bonds. And on reading a bit further, I even find that physicsforums has addressed such bonds before: thread [thread=142490]Coordinate Covalent Bonds[/thread].

What does CO2 have to do with the low abundance of heavy noble gases?

Cheers -- Sylas

Hi Sylas,

We are looking for the continuous source of CO2 to resupply the planet's atmosphere, as CO2 is constantly removed from the atmosphere, if it is not replenished, all plant life will die, if it is not replenished. The last couple of comments have looked at what is known about the early atmosphere to look for clues about the mechanisms and facts that the correct mechanism must explain. (i.e. Constraints for the correct solution.)

Data and analysis supports the hypothesis that the moon was formed from the late impact of a Mars sized body with the proto-earth. When the moon formed, the Earth's early atmosphere was removed. The question is what is the source of the planet's oceans and atmosphere, after that event?

The late chondritic veneer hypothesis proposes a solution using late bombardment of chondritic comets, to create an atmosphere and ocean. There are, however, a number of problems with that hypothesis. The He3 in the planet's oceans is a fraction of what is found in comets which indicates the source of the planet's oceans is not a late bombardment of comets.

A second and less discussed problem is the amount of noble gases in the atmosphere. The late veneer hypothesis has the majority of the volatile elements deposited on the Earth's surface by the late bombardment of comets. The majority of the Earth's CO2 is hypothesized to precipitate out moving into the outer crust of the planet, at that time. (Carbon in the outer crust is found at a concentration that is roughly 200 times greater than what is found in the mantel.) As noted above, that would require an initial atmosphere which roughly 80 time more dense than the current atmosphere. As 80 times the current atmosphere density is required, there should be super solar abundances of noble elements in the atmosphere. (i.e. The majority of CO2 leaves that atmosphere and moves in the outer crust, but noble elements cannot and hence should be found at super solar and super chrondric levels.) This is not the case. Noble elements in the atmosphere are equal to or less than solar and chrondric comets.

An alternative hypothesis to explain the formation and evolution of atmosphere was championed by the late Thomas Gold. That hypothesis was the Earth's CO2 and H2O from the planet's core which is gradually injected over time. Gold provides evidence for the gradual release hypothesis in detail in his book "The Deep Hot Biosphere", which is available in synopsis form on the web.

With the gradual release hypothesis CH4 is continually injected into the atmosphere so the oceans increase in volume over time which explains the missing sedimentary rock in the early geological record. A gradual release also allows time for the geomagnetic field to form which protects the atmosphere from stripping by the solar wind.

Now accepting Gold's hypothesis as a strawman (i.e. Assume the hypothesis could be correct and then try to understand its associated mechanisms and associated predictions.), there is now a continuous source of CH4 to supply the atmosphere. What would modulate that continuous source of CH4? Why are CO2 levels at their lowest levels in 500 million years?

http://www.astrobio.net/news/index.php?name=News&file=article&sid=2708&theme=Printer

http://www.springerlink.com/content/k641167267t84108/

 

[Saul]

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1692179

The following is an excerpt from Berner's paper that discusses the question what stops CO2 from become too high or too low in the atmosphere? (i.e. Too low planet freezes and all plants die. Too high, planet becomes perhaps too hot.)

Table 1 shows that the total amount of carbon in the atmosphere is very small compared with the total amount of Carbon in rocks from both organic and inorganic sources.

As volcanic and tectonic rates vary significant what regulates CO2 in the atmosphere?

The carbon cycle and CO2 over Phanerozoic time: the role of land plants by Robert A. Berner

Table 1. Masses of carbon in various reservoirs
Location___________Mass (10^18 g of C)
carbonate in rocks____________ 60,000
organic C in rocks ____________15,000
ocean HCO3 +CO3 ___________42
soil carbon___________________ 4
atmospheric CO2 ______________0.7
biosphere____________________0.6

Demonstration of the quantitative dominance of the long-term cycle on a multimillion-year time-scale can be seen from table 1. The amount of carbon present in all life is about 0.6 10^18 g of C. By comparison, the amount of organic carbon (kerogen, coal, hydrocarbons) stored in rocks is roughly 15 000 10^18 g, and about 60 10^18 g of this is weathered, or formed by burial in sediments, in 1,000,000 years. Thus, about 100 times as much C as exists in life (or in the atmosphere) is turned over every million years as part of the long-term carbon cycle.

Exchange imbalances, however, must be very small. There is extremely little CO2 in the atmosphere compared to that in rocks (table 1), so that over a few million years if inputs and outputs were not closely balanced, the atmosphere would become overwhelmed with CO2. This is shown in figure 2. Just a 25% sustained imbalance in the Urey reactions results in complete loss of CO2 or extremely high values (note the logarithmic scale). If atmospheric CO2 had varied this much over the past 550 million years, the Earth, because of the atmospheric greenhouse e¡ect, would have been too hot or too cold to preserve life.

 

[Xnn]

The icy objects that collided with Earth over 4 billion years ago, probably do not perfectly match modern comets. There are no precise measurements of the composition of all the different comets anyways, but they are mostly water, ammonia and methane. With ultravoilet radiation and phytosynthesis, this can be converted into water, nitrogen, oxygen and carbonates with excess hydrogen being ejected to outer space.

Popular press books that argue for attention sometime do so at the expense of reality. This includes those that propose free thinking revolutions to science; such as Tom Golds. However, if there is anything to it, then it will will be found in the higher level peer review science journals.

The Azolla event may be responsible for CO2 levels being so low: arctic ocean covered with fresh water allowing oxygen free bottom to sequester carbon.

 

[Saul]

The icy objects that collided with Earth over 4 billion years ago, probably do not perfectly match modern comets. There are no precise measurements of the composition of all the different comets anyways, but they are mostly water, ammonia and methane. With ultravoilet radiation and phytosynthesis, this can be converted into water, nitrogen, oxygen and carbonates with excess hydrogen being ejected to outer space.

Popular press books that argue for attention sometime do so at the expense of reality. This includes those that propose free thinking revolutions to science; such as Tom Golds. However, if there is anything to it, then it will will be found in the higher level peer review science journals.

The Azolla event may be responsible for CO2 levels being so low: arctic ocean covered with fresh water allowing oxygen free bottom to sequester carbon.

Xnn,

Origin of the Earth's Atmosphere
Are you suggesting comet's change over time? Where isotopes and elements are created as time passes? The late veneer theory where by the Earth's atmosphere is created by a special group of comets is not plausible.


CO2 level variance in the atmosphere
1) CO2 must be constantly be produced as there is a net loss as carbon is sequestered. As I noted there are massive increases in carbon that observed in the paleoclimatic record have no explanation.

2) The current long term drop in CO2 levels does not have an explanation.

3) The drop of CO2 levels in the glacial phase by 90 ppm to 100 ppm does not have an explanation.

No one has taken the multiple strawman suggested mechanisms and used them to explain the observations.

Thomas Gold's Theory
As a number of authors have noted the late veneer theory of the formation of the atmosphere was disproved by recent comet isotopes observations. It is clear from your comment that you have not looked into Gold's theory and the observations that support his theory. I will when I have time start a separate thread to outline both the theory and the observations. Please differ a decision until you have had a chance to think about observations and the theory.

Comment:
As there is a list of unexplained anomalies, it makes sense from a process standpoint (if the objective is solving the problem) T

 

[Saul]

The icy objects that collided with Earth over 4 billion years ago, probably do not perfectly match modern comets. There are no precise measurements of the composition of all the different comets anyways, but they are mostly water, ammonia and methane. With ultravoilet radiation and phytosynthesis, this can be converted into water, nitrogen, oxygen and carbonates with excess hydrogen being ejected to outer space.

Popular press books that argue for attention sometime do so at the expense of reality. This includes those that propose free thinking revolutions to science; such as Tom Golds. However, if there is anything to it, then it will will be found in the higher level peer review science journals.

The Azolla event may be responsible for CO2 levels being so low: arctic ocean covered with fresh water allowing oxygen free bottom to sequester carbon.

Xnn,

Origin of the Earth's Atmosphere
Are you suggesting comet's change over time? Where isotopes and elements are created as time passes? The late veneer theory where by the Earth's atmosphere is created by a special group of comets is not plausible. (Some authors suggested to keep the theory alive an interaction with a body of comets from a different comet cloud, however, basic orbital theory shows that is not possible. i.e. There would be observed effects (multiple bands of comets created) which there is not. It is not possible to strip a few comets from the a cloud, and so on.)


CO2 level variance in the atmosphere
1) CO2 must be constantly be produced by some source on the Earth as there is a net loss as carbon is sequestered. As I noted there are massive increases in carbon that are observed in the paleoclimatic record that currently has no explanation. To explain the current observations the source of CO2 for the atmosphere must modulate on a long term basis. Where is the source of the carbon? What is modulating it?

2) The current long term drop in CO2 levels does not have an explanation.

3) The drop of CO2 levels in the glacial phase by 90 ppm to 100 ppm does not have an explanation.

No one has taken the multiple strawman suggested mechanisms and used them to explain the observations.

Thomas Gold's Theory
As a number of authors have noted the late veneer theory of the formation of the atmosphere was disproved by recent comet isotopes observations. It is clear from your comment that you have not looked into Gold's theory and the observations that support his theory. I will when I have time start a separate thread to outline both the theory and the observations. Please differ a decision until you have had a chance to think about observations and the theory.

 

[Xnn]

Xnn,

Origin of the Earth's Atmosphere
Are you suggesting comet's change over time? Where isotopes and elements are created as time passes? .

No. Rather that the icy objects that impacted Earth 4 billion years ago do need to match the comets that we observe now. For instance, they originated from different regions of the solar system. Comets come from the outer reaches, whereas the icy objects impacting Earth were probably formed in the general vicinity of Earth's orbit. They were basking in relatively intense sunlight for a few million years before impacting earth. This could have preferentially stripped off some materials. Also, I suspect they were much larger than comets. Probably more like planetiods.

CO2 level variance in the atmosphere
1) CO2 must be constantly be produced by some source on the Earth as there is a net loss as carbon is sequestered. As I noted there are massive increases in carbon that are observed in the paleoclimatic record that currently has no explanation. To explain the current observations the source of CO2 for the atmosphere must modulate on a long term basis. Where is the source of the carbon? What is modulating it?

Volcanos! Nobody ever said that the rate of volcanism is constant. As the continental plates more around the earth, the rate of volcanic erruption varies.

CO2 levels in the atmosphere are modulated by weathering of rocks. Rocks containing calcium and magnesium are best. The rise of the Himilayians, which exposed rocks subject to weathering has been proposed as a mechanism for the long term decline of CO2 levels.

However, another possible explanation is the Azolla event. That is the artic ocean becamae isolated and a layer of fresh water covered the surface. The salt water bottom then became anoxic and allowed azollas to become sequestered.

2) The current long term drop in CO2 levels does not have an explanation.

The uplift of mountain ranges and subsequent weathering are AFAIK, the leading explanation.

http://www.sciencedaily.com/releases/2006/10/061025185539.htm

3) The drop of CO2 levels in the glacial phase by 90 ppm to 100 ppm does not have an explanation.

Silly me, but I thought it had to do with the hydrologic cycle. During interglacials, the oceans are warm and precipitation is high. This means more weathering of rocks and greater sequesteration of CO2. As the ice sheets advance and the oceans cool, global preciptation diminishes and not as much CO2 is sequestered and a new lower baseline is established; roughly 100 ppm less.

Thomas Gold's Theory
It is clear from your comment that you have not looked into Gold's theory and the observations that support his theory. I will when I have time start a separate thread to outline both the theory and the observations. Please differ a decision until you have had a chance to think about observations and the theory.

If he has relevant articles that were published in higher level peer review science journals, then I'll consider them very carefully. However AFAIK, Gold's theory has never been used to identify potential locations for any oil deposits let alone actually discover any.

 

[chriscolose]

The full range of CO2 variation over glacial-interglacial cycles involves multiple things going on. Another mechanism is found in this recent Science paper
http://www.sciencemag.org/cgi/content/abstract/323/5920/1443

I know I shouldn't post blog links here, but I wrote a summary of the paper at the below link, and the primary author of the study also commented (rather lengthy) which provides good insight into the topic question
http://chriscolose.wordpress.com/2009/03/14/a-new-hypothesis-for-deglacial-co2-rise/

 

[Saul]

No. Rather that the icy objects that impacted Earth 4 billion years ago do need to match the comets that we observe now. For instance, they originated from different regions of the solar system. Comets come from the outer reaches, whereas the icy objects impacting Earth were probably formed in the general vicinity of Earth's orbit. They were basking in relatively intense sunlight for a few million years before impacting earth. This could have preferentially stripped off some materials. Also, I suspect they were much larger than comets. Probably more like planetiods.

Saul:
There comets formed from a large cloud have gas and should hence have the same percentage of elements and isotopes. There is no mechanism to isolate and elements and isotopes in a gas cloud. There is a very short period when the late veneer theory requires the rain of unique comets. Where are the unique comets now?

Xnn: Volcanos! Nobody ever said that the rate of volcanism is constant. As the continental plates more around the earth, the rate of volcanic erruption varies.

CO2 levels in the atmosphere are modulated by weathering of rocks. Rocks containing calcium and magnesium are best. The rise of the Himilayians, which exposed rocks subject to weathering has been proposed as a mechanism for the long term decline of CO2 levels.

However, another possible explanation is the Azolla event. That is the artic ocean becamae isolated and a layer of fresh water covered the surface. The salt water bottom then became anoxic and allowed azollas to become sequestered.


The uplift of mountain ranges and subsequent weathering are AFAIK, the leading explanation.

http://www.sciencedaily.com/releases/2006/10/061025185539.htm

Saul:
There is no evidence for less or more volcanic activity in this period. What could be causing the increase or decrease in volcanic activity for 10 millions of years. Why is the Earth continuing to cool?

If the cause of the long term drop in CO2 was due to more efficient sequestering of CO2 in the arctic ocean when it was fresh, then Co2 levels should gradually rise now.

The formation of the Himalayan mountains cannot explain the drop. There is negative feedback due to reduced CO2 dissolved in water that regulates that processes. There is also if I remember a problem of timing.

Xnn: Silly me, but I thought it had to do with the hydrologic cycle. During interglacials, the oceans are warm and precipitation is high. This means more weathering of rocks and greater sequesteration of CO2. As the ice sheets advance and the oceans cool, global preciptation diminishes and not as much CO2 is sequestered and a new lower baseline is established; roughly 100 ppm less.

Your mechanism is inverted. When there is less precipitation there should be less CO2 sequestered which should mean CO2 levels rise when the planet cools and there is less precipation. CO2 levels fall however during the glacial phase.

Xnn: If he has relevant articles that were published in higher level peer review science journals, then I'll consider them very carefully. However AFAIK, Gold's theory has never been used to identify potential locations for any oil deposits let alone actually discover any.

Saul: I will when I have some time start a thread to discuss Gold's hypothesis. The facts support Gold's hypothesis.