Global warming has been causing the "bleaching" of coral reefs. A bleached coral reef has lost its photosynthesizing symbiotic organisms, called zooxanthellae. It may look white as a ghost — as in the picture above — but it is not yet dead. If the zooxanthellae come back, the reef can recover.
With this year’s record high temperatures, many coral reefs are actually dying:
• Dan Charles, Massive coral die-off reported in Indonesia, Morning Edition, August 17, 2010.
DAN CHARLES: This past spring and early summer, the Andaman Sea, off the coast of Sumatra, was three, five, even seven degrees [Fahrenheit] warmer than normal. That can be dangerous to coral, so scientists from the Wildlife Conservation Society went out to the reefs to take a look. At that time, about 60 percent of the coral had turned white – it was under extreme stress but still alive.
Caleb McClennen from the Wildlife Conservation Society says they just went out to take a look again.
DR. CALEB MCCLENNEN: The shocking situation, now, is that about 80 percent of those that were bleached have now died.
CHARLES: That’s just in the area McClennen’s colleagues were able to survey. They’re asking other scientists to check on coral in other areas of the Andaman Sea.
Similar mass bleaching events have been observed this year in Sri Lanka, Thailand, Malaysia, and other parts of Indonesia.
For more, see:
• Environmental news service, Corals bleached and dying in overheated south Asian waters, August 16, 2010.
It’s interesting to look back back at the history of corals — click for a bigger view:
Corals have been around for a long time. But the corals we see now are completely different from those that ruled the seas before the Permian-Triassic extinction event 250 million years ago. Those earlier corals, in turn, are completely different from those that dominated before the Ordovician began around 490 million years ago. A major group of corals called the Heliolitida died out in the Late Devonian extinction. And so on.
Why? Corals live near the surface of the ocean and are thus particularly sensitive not only to temperature changes but also changes in sea levels and changes in the amount of dissolved CO2, which makes seawater more acid.
We are now starting to see what the Holocene extinction will do to corals. Not only the warming but also the acidification of oceans are hurting them. Indeed, seawater is reaching the point where aragonite, the mineral from which corals are made, becomes more soluble in water.
This paper reviews the issue:
• O. Hoegh-Guldberg, P. J. Mumby, A. J. Hooten, R. S. Steneck, P. Greenfield, E. Gomez, C. D. Harvell, P. F. Sale, A. J. Edwards, K. Caldeira, N. Knowlton, C. M. Eakin, R. Iglesias-Prieto, N. Muthiga, R. H. Bradbury, A. Dubi and M. E. Hatziolos, Coral reefs under rapid climate change and ocean acidification, Science 318 (14 December 2007), 1737-1742.
Chris Colose has a nice summary of what this paper predicts under three scenarios:
1) If CO2 is stablilized today, at 380 ppm-like conditions, corals will change a bit but areas will remain coral dominated. Hoegh-Guldberg et al. emphasize the importance of solving regional problems such as fishing pressure, and air/water quality which are human-induced but not directly linked to climate change/ocean acidification.
2) Increases of CO2 at 450 to 500 ppmv at current >1 ppmv/yr scenario will cause significant declines in coral populations. Natural adaptive shifts to symbionts with a +2°C resistance may delay the demise of some reefs, and this will differ by area. Carbonate-ion concentrations will drop below the 200 µmol kg-1 threshold and coral erosion will outweigh calcification, with significant impacts on marine biodiversity.
3) In the words of the study, a scenario of >500 ppmv and +2°C sea surface temperatures “will reduce coral reef ecosystems to crumbling frameworks with few calcareous corals”. Due to latitudinally decreasing aragonite concentrations and projected atmospheric CO2 increases adaptation to higher latitudes with areas of more thermal tolerance is unlikely. Coral reefs exist within a narrow band of temperature, light, and aragonite saturation states, and expected rises in SST’s will produce many changes on timescales of decades to centuries (Hoegh-Guldberg 2005). Rising sea levels may also harm reefs which necessitate shallow water conditions. Under business-as-usual to higher range scenarios used by the IPCC, corals will become rare in the tropics, and have huge impacts on biodiversity and the ecosystem services they provide.
The chemistry of coral is actually quite subtle. Here’s a nice introduction, at least for people who aren’t scared by section headings like “Why don’t corals simply pump more protons?”:
• Anne L. Cohen and Michael Holcomb, Why corals care about ocean acidification: uncovering the mechanism, Oceanography 22 (2009), 118-127.
Azimuth 
Your link to the last paper is broken. It should be http://www.tos.org/oceanography/issues/issue_archive/issue_pdfs/22_4/22-4_kleypas.pdf
Sunblock, especially high SPF versions abundantly slathered upon pale dermis, could easily devastate photosynthetic marine organisms.
1) Heavily touristed and studied coral reefs would suffer anomalous bleaching, plus down-current plumes of bleaching, and
2) Enviro-whiners screaching “proximity is not causality” in the manner that Global Warmists decry the saturated spectral lines of CO2 while ignoring “ecological alternative” hydrochlorofluorocarbon refrigarant crappy working fluids with 10,000+ times the IR-trapping intensity of CO2 and operating in formerly transparent atmospheric spectral windows.
To “do something about it,” gene-gineer high temp coral symbionts and seed bleached regions. That solves the Official problem. A social advocate makes virtue of failure. The worse the cure the better the treatment – and the more that is required.
Female hormone pharma (contraception and menopausal hormone replacement) survives sewage treatment. SSRI anti-depression pharma (e.g., Prozac) ditto. Recreational pharma ditto. The first two empirically exert massive deleterious impacts upon aquatic life downstream: male fish are feminized, shellfish are reproductively disordered, considerable collected observations “remain to be published.”
This is neither the first warm interglacial period nor the warmest interglacial period. 300 ppm CO2 levels are not even interesting. The difference is anthropogenic sewage – especially the imposed Enviro-whiner trinity of expensive, shoddy, deadly pruning the tree of knowledge by displacing proven technologies with Tinker Bell’s butt dust.
Hi, Uncle Al! Interesting suggestions.
I know there are lots of bad consequences to the massive release of hormones into the environment, including feminization of male fish in rivers that get a lot of waste water effluent. Are you suggesting that this is what’s killing coral? I haven’t heard of hormonal effects in oceans.
Or are you saying that sunblock is the cause?
As far as I can tell, while small outbreaks of coral bleaching can be attributed to many causes, the mass coral bleaching events, and the current dieoff, are correlated to ocean temperatures. For example, a really big coral bleaching event occurred during the 1998 El Niño, and this is another El Niño. But there’s a lot more evidence than that. Try reading this:
• Paul Marshall and Heidi Schuttenberg, A reef manager’s guide to coral bleaching.
A little taste:
You write:
The last interglacial this hot occurred about 400,000 years ago. With just 1°C more warming it’ll be the hottest it’s been in the last 1,350,000 years. Weather isn’t climate, and they didn’t have weather stations back in the Pleistocene, but as far as I can tell, this summer could easily be one of the hottest summers in the last 1,350,000 years.
So sayeth thou.
By the way: Calling people rude names like ‘whiner’ isn’t allowed on this blog. I’ve made an exception this once for you because I know this is your typical tone of voice and I value your expertise in chemistry — but I won’t allow it in the future. For one thing, it’ll piss people off and make my job as moderator harder.
People who are tempted to take Al’s bait and flame back: your posts won’t show up, so don’t bother.
rude names like ‘whiner’ Point taken for local rules of engagement.
An engineer’s first task in solving a problem is to determine its real world cause. Consonant warming of Mars, Jupiter, and Saturn falsify a purely anthropogenic sourcing of terrestrial “warming,” itself suffering manipulated data.
“We must do something” is not “we must do something pertinent.” Politics is a stomach: it has no brain; it knows it is hungry, and the inevitable results are somebody else’s problem. Hunger is due to weather, famine is due to politics.
The Earth is pushing 7 billion people when family size is trivially restrained. The vast majority is atechnological, even within the First World, but it has its votes. Earth is stripped of all easily obtainable resources. Its food productivities are flensed to the bone. Its wastes are planetary. The planet is dying. Best case we are increasingly screwed. Current case we are imploded.
Technology has always found ways to make way more from much less, teosinte to Intel. Luddite recidivism is common: Dark Ages, Cambodian Khmer Rouge, Cuba until it switched from snit to productivity. Sacrifice only engenders more sacrifice. Conservation is a crock – do the maths. March or die.
The ongoing Harvard ethics scandal is emblematic of social engineering. Reality is not a peer vote. We are not passengers on Spaceship Earth, we are crew. Anybody who will not swab the decks is out the airlock – or we all are.
Finally… Is there a loophole in physics? Can we satisfy what is but find a way out, as whale oil became petroleum? 2000 years of Euclid were not dinged by triangles on the Earth’s surface always containing more than 180 degrees. Physics cannot imagine mass distribution chirality, for no fundamental symmetry can be emergent. That is why I call for one modest experiment that cannot possibly work – unless it does. Do opposite shoes vacuum free fall identically?
The worst it can do is succeed.
Physics is not stupid, nor is chemistry. The only way to know is to look. Discovery is always insubordinate. Mediocrity is a vice of the doomed. Somebody should look. We are well and truly screwed if what we have is all there is.
I wrote:
Hoegh-Guldberg et al, in the abstract of their paper “Coral reefs under rapid climate change and ocean acidification”, put it a bit more conservatively:
But we’re not disagreeing much. The point is that the temperature record for the last 1.35 million years shows a peak around 420,000 years ago. We’re getting close to overtaking that peak. Once we pass that peak, it seems like it’ll be the hottest it’s been for 1.35 million years — or more, I’m not sure how much more.
Err, I meant http://www.tos.org/oceanography/issues/issue_archive/issue_pdfs/22_4/22-4_cohen.pdf . . . should really be more right when correcting people :)
Thanks! Fixed it.
Just to note that there are extensive populations of (relatively) deep-water corals that are also vulnerable.
Uncle Al reminded me: I shouldn’t just bemoan the death of coral reefs, I should say a bit about how to “do something about it”, and solicit suggestions from all of you.
Here’s what Hoegh-Guldberg has to say:
The big problem is global warming. This will not be stopped by small individual actions like replacing our light bulbs and the like — though it’s good to do all that stuff as part of an overall movement towards greater intelligence in energy usage. So, I think Hoegh-Guldberg is doing us a disservice in acting as if these small actions are significant steps towards solving that problem. As far as I can tell, only something like a carbon tax or cap-and-trade system can fix the big gaping externality of CO2 pollution.
However, he knows about coral reefs, so his points 1)-3) are very useful. In particular: it’s not instantly obvious that algae-eating herbivores like sea urchins and parrotfish can help coral reefs survive! But it goes like this, apparently: after a reef gets bleached, it has a lot more trouble bouncing back to good health if it gets covered with algae.
Farming corals sounds cool, especially if people can figure out how make money off it somehow, so they do it without anyone forcing them. Ideas?
I also wonder if some types of coral that may otherwise go extinct can be saved in artificial environments — big aquaria, basically.
Genetically engineering or breeding corals that can survive higher temperatures is also fine with me, if we can do it!
More important is the political message that everyone (or at least a vast majority) acknowledges that there are global effects of local resource consumption and the responsibility to do something about it, even if that is inconvenient. In Germany there was a long debate amongst politicians if waste separation had a chance to become accepted, with counter arguments like “people won’t accept to have three different trash cans in their kitchen”.
But it worked, smoothly, and now similar policies are installed without much fuss, see:
EU to switch off traditional light bulbs by 2012.
IMHO these small steps – with more symbolic significance than effects – are necessary before anyone has the courage to suggest more drastic measures (“anyone” is addressing people who are at risk to lose a significant amount of power, wealth and reputation if they publicly voice opinions that are unanimously repudiated by the mainstream, like MoP :-).
Tim wrote:
I agree that this is an important message. Back home in Riverside I have replaced my lightbulbs with compact fluorescents, I recycle trash religiously, and I have set up a composting bin. Only the last would be considered weird.
Here in Singapore there is no obvious way to recycle trash, and I think that’s shockingly backward. The lightbulbs are all fluorescent, but people blast the air conditioning at ridiculously cold temperatures — and indeed a repair man in our apartment complex suggested that leaving the air conditioner set at a temperature as high as 28°C (as we do) could damage the unit. Is that true??? I got the feeling he was just offended by the idea of someone living at such a high temperature. It’s a bit hard to have a personal compost pile when you live in an apartment, but I might try one on the balcony. (It might attract a bunch of scary tropical insects, and then lizards.)
In Shanghai people just set their trash in plastic bags by the entrance to the apartments, and workers take these bags to a large building in the apartment complex and sort it out by hand! — they have more poor people there. Semi-feral cats control the rodents that tend to accumulate in these trash heaps.
All these things matter.
What I meant was that if someone asks “what can we as a society to help coral reefs survive?”, and your main answer regarding carbon emissions is “switch to compact fluorescent light bulbs and use energy efficient appliances and vehicles”, that could lull people into thinking that’s enough action to solve the problem. And that would be a dangerous illusion: it’s nowhere near enough. The problem is orders of magnitude bigger than that.
As someone put it: if everybody does just a little to help prevent global warming… just a little will get done. And as someone else put it: we need to change our leaders, not just our lightbulbs.
That’s probably true. However, in the United States there are well-respected people in Congress who have been working hard to pass cap-and-trade legislation for CO2. Their efforts fell through this year, but it is important to keep thinking and talking about such ideas: they have a lot of support, just not enough yet.
Is the link behind “Hoegh-Guldberg” broken?
Whoops – I left out the “http://” part. Fixed – thanks!
You may be interested in an international research project called FORCE (Future of Reefs in a Changing Environment), one of their projects is about conserving and re-breeding corals, as you can see here.
Thanks!
I’m glad this topic has come up. I’ve got a few questions.
The equilibrium in question is
CO2+H2O ⇌ H2CO3 ⇌ HCO3– + H+ ⇌ CO32- + 2H+
If you take a carbonate solution and add another acid, like hydrochloric acid, it adds hydrogen ions to the right hand side of the equation, which by Le Chatelier’s principle, pushes the equilibrium to the left. CO3 is converted to bicarbonate and CO2.
What if you add CO2 on the left hand side? Why does this not push the equilibrium rightwards? (Please be careful not to use diagrams that assume constant DIC.) I’d be very interested in a proper explanation of this. (I suspect it’s true, but I don’t understand it.) And I’m not afraid of explanations involving rate constants.
If you take pure water and dissolve CO2 in it, the pH goes down. Which has more carbonate ions in it? Does lower pH always mean lower CO3?
Second question: the Earth’s history goes back more than a million years. What was the atmospheric CO2 level at the time corals first evolved?
The solubility of CO2 varies significantly with temperature. How far does pH vary, from freshwater to seawater, tropics to poles, surface to the deeps? How much from day to day, with turbulent mixing? How much does the shallow water temperature of the sea vary over the year? (Note, I mean the temperature, not the temperature anomaly.)
Fourth, Charles Darwin reported on the mechanism of the formation of coral atolls – something else he did on his travels. He said that atolls were at sea level or in shallow waters because the islands grew from coral and coral growth was limited by the surface, not the other way round. Given that coral species have already survived meltwater pulse 1a, can you say what the maximum growth rate of coral is, and what rate of sea level rise would exceed it? Is this rate less than what the IPCC projects?
Thanks.
I can’t answer your questions, at least not instantly — but they’re very interesting, so I hope some chemists and biologists jump in and help out. This is precisely the sort of thing I want to do here at Azimuth: join forces to figure things out.
All I can do instantly is quote some mildly relevant passages from the paper I cited:
• Anne L. Cohen and Michael Holcomb, Why corals care about ocean acidification: uncovering the mechanism, Oceanography 22 (2009), 118-127.
These passages don’t exactly answer your chemistry question, but they provide some clues that are worth pondering:
And then:
And this is where things get complicated… read the paper for more.
But returning to your chemistry question, which is much more basic — pardon the pun — I guess the most relevant passage was Ocean acidification reduces the pH and thus the abundance of carbonate ions in seawater. But what you’re asking is: why?
By the way, I mentioned coccolithophores above, so it’s worth noting that they could be very important.
Nullius wrote:
Some scholars claim it was created on the night before October 23rd, 4004 BC — but I’m inclined to agree with you here.
Good question! Yes, whenever I mention how temperatures and CO2 levels may soon soar above those we’re used to in late-Pleistocene interglacials, I think about how these conditions are still cold compared to earlier times. I’m no expert — indeed, the only reason I’m trying to answer your question is to learn stuff — but I believe the danger to corals has a lot to do with the suddenness with which conditions are changing. If conditions changed slowly enough, the corals could migrate to temperatures they liked, or even evolve to adjust. But we are seeing CO2 levels, and I believe temperatures as well, rise at spectacular rates.
(These rates may not be unprecedented: witness for example the Paleocene-Eocene Thermal Maximum. But a lot of stuff died during that episode.)
A bit more on coral’s adaptive abilities before I actually come around to your question. From:
• CRC Reef Research Centre, Coral bleaching and global climate change.
Okay, now back to your actual question: “What was the atmospheric CO2 level at the time corals first evolved?”
As I explained, corals of significantly different kinds have evolved several times in the Earth’s history, so the first corals were quite different from those we see today. I know practically nothing about those early corals, so I’ll stick to the corals we see today.
The kind we see today are the Scleractinia, or stony corals. They showed up about 220 million years ago, in the Middle Triassic. They filled a niche that was left open when the two main previous types of coral died out in the Permian-Triassic Extinction Event — along with 90% of all marine species.
So, you are asking me about the atmospheric CO2 concentration in the Middle Triassic (and later).
Of course my instant reaction is that there must be considerable uncertainty when it comes to questions like this. But I can browse the web with the best of them, and pull up a chart like this:
And indeed, there’s quite a spread of opinion (click for more info) — but we see that CO2 levels in the late Triassic and late Cretaceous may have hit a whopping 2000 ppm.
In case anyone out there hasn’t been keeping score, it’s only about 390 ppm today. So, clearly corals have survived much higher CO2 levels. It was also much warmer back then: for parts of the the Cretaceous, tropical sea surface temperatures may have commonly reached 35 C!
Did corals live in the tropics then, or did they prefer cooler locations? I don’t know.
Anyway: since the end of the Cretaceous around 65 million years ago, when the dinosaurs went extinct, it’s generally been getting colder, and CO2 levels have been dropping. So, to repeat myself: I’m not sure that what corals once tolerated long ago has much to do with what they can tolerate suddenly today.
Just to note that given sufficient time the ocean will buffer the acidity, meaning that pH wouldn’t have been much different from current even with much higher atmospheric CO2. A fast rise in CO2 will be accompanied by an increase in acidity, as we are seeing.
Do you know any place one can read a simple description of the chemistry involved? You’re making it sound like Nullius in Verba’s comment:
is exactly on target: namely, that the acidification is not an equilibrium effect, so understanding it requires thinking about reaction rates.
I’m certainly no expert, but I think one can speak in terms of a short-term equilibrium since the buffering process takes such a long time.
As for a comprehensive chemistry discussion, I’m not sure. Jean-Pierre Gattuso (who runs the EPOCA blog) should be able to give you a pointer.
Steve wrote:
Okay, I’ve changed my mind. I now think you’re right here: equilibrium chemistry should be enough to answer this question:
Why does adding CO2 to seawater make it more acid and reduce the level of CO3– (“carbonate”)?
An outline of the answer can be found in Kleypas and Langdon and the Royal Society report. But, it’s subtle.
See this discussion of a new paper on the Aptian acidification event (~121 mya). Of interest is the length of time it took for pH to return to normal. There’s nothing about corals, although at least some survived.
Also, EPOCA (the European Project on Ocean Acidification) has a very active blog. They don’t seem to miss much.
For anyone out there who is feeling really confused, it might help to start with this cheat sheet. Plain old water actually does fancy stuff like split into protons and hydroxide:
H2O = water
H+ = proton
OH– = hydroxide
But in fact a lone proton is very aggressive, so it usually latches onto a water molecule to form hydronium:
H3O+ = hydronium
There’s a lot more to this story… water is incredibly complex… but there’s no time for that now.
When you add carbon dioxide even more things form:
CO2 = carbon dioxide
H2CO3 = carbonic acid
HCO3– = bicarbonate
CO32- = carbonate
Carbonate looks like this:
Stick a proton on one of the oxygens here and you get bicarbonate (an illogical name; the chemistry nomenclature gurus prefer ‘hydrogen carbonate’). Stick on another proton and you get carbonic acid.
Okay, now read what Nullius wrote:
You’re making me feel I need a refresher course on chemistry! The Wikipedia writes the reaction a bit differently and seems to sidestep your paradox by bringing calcium carbonate into the game:
Thank you!
All of that is enormously helpful. Even if they don’t quite answer all the questions, they do move things forward. And I applaud your approach.
You’re absolutely right about the biological complexities. Life exists in a wide range of pH’s, each type of organism adapted to its own niche. Freshwater shellfish tolerate a far lower pH than found in salt water, for example. The tolerance of any particular species has more to do with its own individual biochemistry than any fundamentals of inorganic chemistry.
But I was already struggling to follow the basic chemistry without diving into the biology just yet.
The thing is, I strongly suspect that there is a good explanation, but every time somebody gives an explanation of ocean acidification for the general public, the real explanation is seen as too complicated and a simplified version substituted in its place. This makes it very difficult for a sceptic to approach the subject. You want to understand and check the science, not taking some Authority’s word for it. But the explanation on offer seems to have big holes in it. What are you supposed to do?
Adding CO2 does of course reduce pH. CO2 added on the left hand side shifts the balance to the right, increasing H(+) concentration. But there is an essential difference between adding carbonic acid and adding any other acid, and this point constantly gets glossed over. Adding any other acid reduces both pH and CO3 concentration, no argument. But that particular argument doesn’t extend (without modification) to adding CO2.
Introducing calcium ions may indeed have something to do with it, but at first glance it appears to be an equivalent way of writing the reaction we’ve already discussed; the steps all lumped together. The equation also doesn’t show the production of any hydrogen ions required to lower pH. And if you write in the next step implied by that statement “the right-hand side of the reaction produces an acidic compound” and show it acting as an acid, what do you get?
Nullius wrote:
I understand — but alas, my knowledge of chemistry seems approximately equal to yours, so I’m able to see why you’re confused, and be equally confused myself, but I’m not instantly able to help you. (I could probably figure it out with a bit of reading, but I’m kinda hoping that someone reading this knows some chemistry.)
I understand most of your worries but I don’t understand this sentence. What do you mean by “what do you get?” Do you mean “what acidic compound do you get?” or “what conclusion do you draw?”
Hmm, I guess you mean “what acidic compound do you get?”
What I meant was that for HCO3(-) to act as an acid, it means:
HCO3(-) = H(+) + CO3(2-)
i.e. it only acts as an acid by producing more carbonate ions.
In a sense, the calcium carbonate reaction is precisely the opposite of acidification. It is actually a case of the alkaline CaCO3 partially neutralising the (relatively) strong acid CO2 (or H2CO3 as it is in solution) to form a weaker acid HCO3(-). Instead of being able to donate two protons, like CO2, HCO3 can donate only one.
I suspect Wikipedia’s version is related to the IPCC’s AR4 Chapter 7 box 7.3 on page 529. Eqn 7.2 with the addition of Ca(2+) ions on either side would give it. But the IPCC’s version is even more obviously a rearrangement of the same equilibrium. The first step is the same as the first step of Eqn 7.1, and the second step is the second step of 7.1 written backwards.
I honestly wasn’t really expecting you to know the answer. But I thought you might be better placed to find one. A lot of places I ask the question, I’m dismissed as a ‘denier’ and ignored. “Scientists say…” and that’s good enough for them. Whereas you demonstrate the true spirit of scientific enquiry far better by wanting to know the answer yourself, and are less likely to be dismissed.
It may even be relevant to the solution. If it turns out that it is a matter of biology rather than chemistry, maybe we can do something about it by that means. Genetically engineering pH-tolerant corals, for instance?
In any case, I am grateful that you are even asking the question. I’m sure the answers will come in time.
‘Guess’? Well, I assume you don’t require an answer to that, now.
My apologies. I didn’t intend to start any trouble. I’m still grateful that you are asking the question.
No need for apologies!
I’m tracing back the literature, and some papers point to these for information on the underlying chemistry:
• Coral reefs and changing seawater carbonate chemistry, Royal Society Policy Document, 2005.
• J. A. Kleypas and C. Langdon, Coral reefs and changing seawater carbonate chemistry, in: Coral Reefs and Climate Change: Science and Management, edited by: Phinney, J. T., Hoegh-Guldberg, O., Kleypas, J., Skirving, W., Strong, A., American Geophysical Union, Washington, DC, 2006, pp. 73-110.
• S. Doney, V. Fabry, R. Feely, and J. Kleypas, Ocean acidification: the other CO2 problem, Annual Review of Marine Science 1 (2009), 169-192. Available here with subscription.
• K. Caldeira and M. E. Wickett, Anthropogenic carbon and ocean pH, Nature 425 (2003), 365-365. Available here with subscription.
Annex 1 of the first reference and the first few pages of the second one promise to be quite helpful. Reading a good chemistry book might also be good for me.
Anyone want to join in and figure this out?
Nullius: I think you want to understand the section beginning here in Kleypas and Langdon’s paper:
The explanation that follows is not easy.
The discussion here may be getting a bit hard to follow, but I’ve become fascinated by a question Nullius raised, so let me summarize it as follows:
Why does adding CO2 to water decrease the level of carbonate (CO32-)?
Some ideas from chemistry make this seem paradoxical at first glance. But let me show you this graph from the Royal Society report, which shows this effect at work:
I don’t think there’s a really a paradox. Extra CO2 in the water creates carbonic acid (H2CO3) which, being acidic, splits into bicarbonate (HCO3–) and free protons (H+):
CO2 + H2O ⇌ H2CO3 ⇌ HCO3– + H+
The free protons then react with existing carbonate to form bicarbonate:
CO32- + H+ ⇌ HCO3–
So, carbonate levels drop and bicarbonate levels increase.
However, it’s a tricky business, and it would really take some detailed calculations to understand the curves in the graph above!
Thanks for the links.
The Royal Society appendix just appears to repeat the same argument as in the IPCC or Wikipedia. It uses eqn 3 to increase concentrations of H(+) and HCO3(-), which appear on both sides of eqn 4, but only seems to consider the forward effect of the H(+) while failing to discuss the backwards influence of the extra HCO3(-). It doesn’t explain it at all.
However, after struggling to understand both papers, I think I can now see a way to salvage this. The rate equation for eqn 4 would be
[H(+)][CO3(2-)]/[HCO3(-)] = K
where K is a constant for the current temperature, pressure, etc.
If we simplify notation to get hc/b=K, rearrange K/c=h/b, and increase h and b by the same amount d, we get K/c’ = (h+d)/(b+d) = h/b + (b-h)d/(b(b+d)).
Now, if eqn 3 was all that was going on, then b=h and nothing happens. But we know from your second link that this isn’t the whole story. There’s this ‘total alkalinity’ that is also involved.
The Kleypas and Langdon paper also has some confusing aspects, and fails to really explain what is going on. For example, just after eqn 10 it discusses the effect of CaCO3 precipitation which obviously removes both Ca and CO3 ions – but where they only mention the removal of Ca ions and then state that Ca reduces by the conversion of carbonate to bicarbonate. Why does the direct removal of carbonate by precipitation not count?
I think they’re probably right that it does, but I don’t see how their explanation can be the right one.
Similarly, they make an approximation by dropping the Borate alkalinity (which they discuss, and is fair enough) and the hydrogen ion concentration, which they do almost entirely without discussion. With two terms dropped, they then use the remainder as an equality to say that as bicarbonate increases the carbonate must decrease. As explanations go, it’s somewhat lacking.
But again, with the insertion of a few assumptions and missing steps, I can see how to make progress. Eqn 7 seems to be based on the idea that the dissolved ions of the strong acids/bases are fixed, and those of the weak acids/bases adjust to fit. So the top line of eqn 7 may be considered a constant, and the bottom line says that a weighted sum of bicarbonate, carbonate, and hydrogen must be constant. This isn’t telling us anything new, of course. Just that for every hydrogen ion formed, a bicarbonate must turn into a carbonate, or carbon must enter externally from some uncharged species.
But I believe the reason that they neglect the hydrogen ions in TA to consider only Ca instead is that the salts of the strong acids and bases are balanced by carbonate/bicarbonate far in excess of what dissolved CO2 would create. The bicarbonate concentration is a huge number compared to the hydrogen ion concentration. Which brings us back to the end point we reached after considering the Royal Society paper.
With b much greater than h, (b-h)d/(b(b+d)) is positive, and so on adding CO2 the carbonate concentration c decreases. It happens because there’s proportionately a lot more bicarbonate (from other sources) than hydrogen, so the addition of CO2 has proportionately less effect on the bicarbonate, which is why they can just consider the forwards influence of the H(+) and ignore the backwards influence of the HCO3(-).
Fundamental to this argument are the rate equation given above, and the observation that most of the carbonate/bicarbonate is there to balance the strong acid/base salts. (Although there is a logical gap here – why carbonate and not anything else?) Only one paper alludes indirectly to the latter. Neither paper mentions the former. I don’t see how they could have derived the result without them.
I get the distinct impression with both papers that the authors didn’t fully understand why, only that it was so, and they tried to generate an ad hoc explanation that would pass. The reasoning is muddled and imprecise.
Which is concerning.
(I may of course be doing them an injustice – maybe they simply thought the real explanation was too complex. What do you think?)
But I think I can declare myself satisfied. Although there are still gaps and uncertainties in my understanding, I do at least have a plausible explanation now. My thanks!
I forgot to note – their equation for TA also neglects OH(-), which given that the sea is alkaline, is perhaps a significant omission.
However, it doesn’t affect the overall argument.
Balancing equations involving single weak acids and bases can be tricky. It is important to keep in mind that not only are are there multiple species, only *variable* fractions of them are ionized as indicated in the “intuitive” equations, and reality does not follow the “intuitive” stoichiometry.
Correctly balancing equations of multi-buffered systems like seawater (borate is very important, other not so much) is indeed complex. Worse, it’s not even a closed system and there are exchanges with gaseous and solid components!
I tried submitting this before, but it didn’t seem to work.
The Wikipedia page on calcium carbonate is the best thing on this issue that I have found so far. See especially the section on solubility with varying CO2 pressure.
http://en.wikipedia.org/wiki/Calcium_carbonate#With_varying_CO2_pressure
Increasing CO2 pressure causes more calcium carbonate to dissolve in pure water, so I don’t think there is any need to bring in concepts like total alkalinity in order to understand the basic mechanism.
Sorry, Graham, this comment of yours — and perhaps your previous try? — went into my spam box. I don’t know why.
Anyway, thanks for the comment.
Yes, as the pH level of the ocean drops, corals are on the way out. They are among the “walking dead” species, much like the Polar Bears.
John B,
Because of misinformation trumpeted by a few, you may not know that it is U.S. federal policy that climate change is happening, and that federal response is both required and happening e.g. plans to move docks to adapt to changing sea levels. One example is the interagency Climate Change Adaptation Task Force:
http://www.whitehouse.gov/administration/eop/ceq/initiatives/adaptation
Apropos of combining geometry, dynamics, wave-particle duality, phase transitions, and quantum information transmission (but not environmental, alas), it is interesting to me that Moire patterns from interfering holograms have been experimentally useful for decades. But where are the quantum gravity category theorists on this?
John F. wrote:
Thanks for the reminder!
I cheered on the Supreme Court decision that forced the EPA to address the threats due to CO2.
But I didn’t pay enough attention to the subsequent decision by the EPA that:
and
As for what category-theoretic physics says about Moire patterns, this isn’t the right blog entry for discussing that.
In case you don’t know the EPA is mid-process (IIRC they’ve received initial comments and are now writing the rule) for a parallel rule for ocean acidification per the Clean Water Act. This will create an entirely independent legal basis for regulating CO2 since the existing rule is under the authority of the Clean Air Act. It will be interesting to see how all of this unfolds, but an obvious key point is that with a CWA-based rule in place it would be difficult for Congress to gut independent CO2 regulation by the EPA since the only plausible way to do so is by way of a poison pill in a bill adding climate provisions to the CAA. Obama has promised to veto any direct attempt to take away the EPA’s authority.
But with the failure of Congress to act on a climate bill in this session and poor prospects for next session, the question becomes one of what the EPA is willing to do with its considerable authority. Sufficiently strong action would force Congress into trying to cut a deal, but we have yet to see much evidence for a willingness by the administration to engage in that sort of power politics, or indeed to take strong regulatory action absent legislative considerations.
On the plus side, for the first time we have scientists who understand the problem (Chu, Holdren and Lubchenco) in key policy-making positions, and I’m pretty sure they’ll insist on seeing something real in place during Obama’s first term (in part because there’s no guarantee of a second one).
This new paper (press release) on possible rates of acidification during the next century looks interesting, although not good news.
[…] reefs are also having trouble due to warming oceans. For example, there was a mass dieoff of corals this summer off the coast of […]
[…] reefs are also having trouble due to warming oceans. For example, this summer there was a mass dieoff of corals off the coast of […]
This press release describes a new paper finding that an ocean area of naturally low pH (due to volcanic CO2 emissions) points to major biodiversity trouble ahead.
[…] and produce hydrogen ions, leading to ocean acidification. You have already discussed this on your blog. In addition to acidification, the chemical buffering effect is lessened (the Revelle factor […]
This popped up on my radar this morning.
The heat kills Caribbean Coral
Southern Caribbean Sea could be experiencing the beginning of a mass mortality of corals, scientists suggest
http://translate.google.com/translate?js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&sl=es&tl=en&u=http%3A%2F%2Fwww.hoy.com.do%2Fel-pais%2F2010%2F9%2F12%2F341637%2FTierramericaEl-calor-mata-a-corales-caribenos
Ouch! Thanks for pointing that out, Eric. From earlier this year:
• NOAA Warns: Caribbean’s Coral Reefs In Danger This Year.
This looks like an already-in-English version of the page you pointed us to:
• Stephen Leahy, Record Temperatures Killing Caribbean Corals.
Yesterday on Croatian TV there was a woman from Dalmatia who does artistic jewelry out of sea shells. She was very concerned about the polution in the oceans. One of the striking details she was claiming is that even the structure of a shell is clearly falling down with the polution in oceans.
For example the shells from around Indonesia, while they look externally equally nice like the shells from somewhere around New Guinea where the polution is smaller, in fact are much easier to break during working on it (for jewelry purposes); there are more natural fractures and the material is less hard. It would be interesting to know what aspect of polution makes the shells “softer”. I consider the places where such beautiful shells live, relatively clean, so it is interesting that the mechanical properties fall down with relatively low polution.
This page
http://www.whoi.edu/OCB-OA/FAQs/
under
Why does increasing the dissolved CO2 concentration in seawater affect shell building in marine organisms?
says that what sound like small increases in ocean acidity (especially on the logarithmic pH scale) can have significant effects. I guess the question becomes why there’s significant acidity differences at various points around the globe.
There are a bunch of potentially useful links here, though the article itself is not very informative: what, for example, does it mean to say that oysters are ‘functionally extinct’? I still see them for sale.
• State of the ocean: ‘shocking’ report warns of mass extinction from current rate of marine distress, Huffington Post, 20 June 2011.
John wrote:
There is one – and only one – German oyster farm in the north sea at the coast of the island Sylt. The tides have a very strong effect in the north sea; the water line moves several kilometers, so that the oysters are under water half of the time, which is a kind of body building (open shell, close shell, open shell, close shell).
Those oysters are really expensive, but you’ll see them on sale, if you go to the really good chefs, for quite some time after there are no oysters left in the wild.
[…] and produce hydrogen ions, leading to ocean acidification. You have already discussed this on your blog. In addition to acidification, the chemical buffering effect is lessened (the Revelle factor […]
[…] and produce hydrogen ions, leading to ocean acidification. You have already discussed this on your blog. In addition to acidification, the chemical buffering effect is lessened (the Revelle factor […]