Arctic seas turn to acid, putting vital food chain at risk

[bascule]

http://www.guardian.co.uk/world/2009/oct/04/arctic-seas-turn-to-acid

 

Carbon-dioxide emissions are turning the waters of the Arctic Ocean into acid at an unprecedented rate, scientists have discovered. Research carried out in the archipelago of Svalbard has shown in many regions around the north pole seawater is likely to reach corrosive levels within 10 years. The water will then start to dissolve the shells of mussels and other shellfish and cause major disruption to the food chain. By the end of the century, the entire Arctic Ocean will be corrosively acidic.

 

"This is extremely worrying," Professor Jean-Pierre Gattuso, of France's Centre National de la Recherche Scientifique, told an international oceanography conference last week. "We knew that the seas were getting more acidic and this would disrupt the ability of shellfish – like mussels – to grow their shells. But now we realise the situation is much worse. The water will become so acidic it will actually dissolve the shells of living shellfish."

 

Oh my...

[CaptainPanic]

What will really happen is that there will be an equilibrium between the atmosphere and the sea.

There are 2 (or 3) equilibria that work together.

CO2 in air <--> CO2 in water <--> H2CO3

H2CO3 <--> HCO3- + H+

HCO3- <--> CO3(2-) + H+

 

And since the pH of the oceans is about 8, the carbonate and bicarbonate concentrations are relevant.

 

The first equilibrium (between atmosphere and water) is governed by for example Henry's Law which states that the concentration in the air will linearly correspond with the CO2 concentration in the water.

 

The increase in atmospheric CO2 is about a factor 2 (or perhaps 3 in an extreme case?). Therefore, the concentration in the sea will also double or triple.

That in turn will affect the other two equilibria.

 

The main question is now: is it true that this can reduce the pH of the ocean from 8 to below 7?

 

And do shells of sea fish really dissolve already at a pH level of 6.9?

 

At lower pH, when stuff becomes really more acidic the carbonate and bicarbonate concentrations are very low. But in order for the pH to drop an entire point then, the atmospheric concentration must go up 10 times (the pH is a logarithmic scale).

 

Frankly, I don't think that this professor is right (note: I did not yet calculate it). I don't think that a higher CO2 pressure can significantly alter the acid concentration. I think that also between pH of 8 and 7, you need a tenfold increase in partial gas pressure.

 

[edit] deleted my initial post for going off topic - it was some joke about genetically modifying fish to be corrosion resistant

Edited October 13, 2009 by CaptainPanic
going off topic and wanting to provide actual feedback

[iNow]

I suggest that Henry's Law is of limited use in this scenario. The oceans will only absorb so much CO₂ until they become saturated and their ability to absorb more decreases significantly. In fact, a few studies have already shown that the ocean's ability to absorb CO₂ has been steadily decreasing as they get further acidified.

[Moontanman]

The ocean has a very long way to go before it becomes acid. Mid ocean water is around 8.3 or 8.4 pH I've kept and bred both marine fish, invertebrates and live coral. pH change is bad when it is fast but a slow change up and down is not harmful. As long as the pH stays around pH 7.6 to 8.6 and all changes are slow i really think this a case of crying wolf. Much coastal waters hover around 7.5 and up and in some places I have personally measured pH of less than 7 due to acidic freshwater run off. I honestly do not see open ocean pH dropping to below 7 any time soon or even below 8. The ocean is buffered, it resists pH changes due to the carbonate buffering. Any change will by this mechanism be slow. For the shells of ocean creatures to be affected the Ph would have to drop considerably below 7

[SH3RL0CK]

The artic ocean is not independent, a simple glance at the map will show lots of ways artic water mixes with the waters of the Atlantic and Pacific oceans. Surely, the mixing occurs faster than the acidification (esp. since the acidification is also occuring with the Pacific and Atlantic waters). How exactly is the acidification being localized to the artic ocean as the CO2 levels in the atmosphere are fairly constant across the globe?

 

For that matter, doesn't the artic ocean itself mix? Wouldn't this mixing be quicker than any potential localized increase in acidification? Which makes me question statements from the article such as

His research suggests that 10% of the Arctic Ocean will be corrosively acidic by 2018; 50% by 2050; and 100% ocean by 2100.

[Moontanman]

The premise of the OP is extreme exaggeration to begin with. dissolving the shells of living animals would take a pH much under 7 . Shell fish can deposit their shells at pH of much less than 7, less than 5 is not out of the question. The article never mentions the predicted pH and only say sit will be corrosive as acid used to eat scale off a pot or pan pH 3? or less. I'd have to see some real figures to even consider such a thing.

[CaptainPanic]

I suggest that Henry's Law is of limited use in this scenario. The oceans will only absorb so much CO₂ until they become saturated and their ability to absorb more decreases significantly. In fact, a few studies have already shown that the ocean's ability to absorb CO₂ has been steadily decreasing as they get further acidified.

I bet those studies used a model to look at the mass transfer of CO2 into water. And the driving force behind the mass transfer is described by Henry's Law. The deviation from the equilibrium value is the driving force. If you don't know the equilibrium values, you don't know the driving force, and you cannot determine the mass transfer rate (or flux, if you want).

 

It's necessary to consider this, since we are talking about terms like "unprecedented rate". The word "rate" indicates we need to look at time-dependent issues, and Henry's Law is needed for one of those.

 

Apart from that, we might as well ignore the article. I think it's rubbish. Any scientist who describes acidity without the use of the term "pH" cannot be taken seriously. The information in the article was insufficient for a peer review (although the article did not claim to be in a scientific journal).

[bascule]

Here's the paper instead of the crummy news article...

 

http://www.biogeosciences.net/6/1877/2009/bg-6-1877-2009.html

 

Impact of ocean acidification on a key Arctic pelagic mollusc (Limacina helicina)

 

S. Comeau1,2, G. Gorsky1,2, R. Jeffree3, J.-L. Teyssié3, and J.-P. Gattuso1,2

1CNRS-INSU, Laboratoire d'Océanographie de Villefranche, BP 28, 06234 Villefranche-sur-Mer Cedex, France

2Université Pierre et Marie Curie-Paris 6, Observatoire Océanologique de Villefranche, 06230 Villefranche-sur-Mer, France

3Marine Environmental Laboratories, International Atomic Energy Agency, 4 quai Antoine 1er 98000 Monaco, Principality of Monaco

 

Abstract. Thecosome pteropods (shelled pelagic molluscs) can play an important role in the food web of various ecosystems and play a key role in the cycling of carbon and carbonate. Since they harbor an aragonitic shell, they could be very sensitive to ocean acidification driven by the increase of anthropogenic CO2 emissions. The impact of changes in the carbonate chemistry was investigated on Limacina helicina, a key species of Arctic ecosystems. Pteropods were kept in culture under controlled pH conditions corresponding to pCO2 levels of 350 and 760 μatm. Calcification was estimated using a fluorochrome and the radioisotope 45Ca. It exhibits a 28% decrease at the pH value expected for 2100 compared to the present pH value. This result supports the concern for the future of pteropods in a high-CO2 world, as well as of those species dependent upon them as a food resource. A decline of their populations would likely cause dramatic changes to the structure, function and services of polar ecosystems.