Update: Thinner Shells Put Ocean on Thin Ice

by Bill Chameides | March 12th, 2009
posted by Erica Rowell (Editor)

Permalink | 9 comments

Foraminifera (the popcorn like critters here) help form the base of the ocean food web. Trouble for them spells trouble for us.

Some argue that more carbon dioxide is a “good thing.” I guess they just can’t get their minds around the whole climate change thing. OK, but what about ocean acidification? If you like seafood, ocean acidification is definitely not a good thing.

It may turn out that climate change is not the worst consequence of our dependence on fossil fuels. It could be ocean acidification.

Quick Review of Ocean Acidification

The ocean is a slightly alkaline, salty water solution. The alkaline excerpt:encoded means the seas have slightly more dissolved bases than acids.

All liquids can be described in terms of how basic or acidic they are. Acids, which comes from the Latin acidus, meaning sour or sharp, have an excess of hydrogen ions. Vinegar and lemons are common acids. Basic liquids have an excess of hydrogen oxide ions. Ammonia is a common base. The alkalinity of the ocean is fairly close to that of sodium bicarbonate, an antacid taken to counteract heartburn.

So Who Will Be Affected by This Acidification? Very Likely You and Me.

Every time we add carbon dioxide (CO2) to the atmosphere, a portion of the CO2 finds its way into the ocean. But since dissolved CO2 forms a weak acid – carbonic acid – the net effect is to cause the ocean alkalinity to decrease a little bit (and the acidity to increase a bit). If you like swimming, no worries – that extra acidity is way too slight to make a difference to you. But that doesn’t mean you shouldn’t be concerned.

As the ocean becomes more acidic, the process of forming calcium carbonate minerals like calcite and aragonite from dissolved calcium and carbonate becomes increasingly more difficult. For the multitude of ocean creatures that form calcareous shells and skeletons from the dissolved calcium and carbonate ions in the ocean, ocean acidification could be a huge problem. And if it’s be a problem for them, it will be a problem for people.

Calcifying ocean species include corals, mollusks (such as clams and mussels), and single-celled creatures at the bottom of the food chain called protists. (These include plankton like coccolithophores and foraminifera.) Since coral reefs are home to many of the world’s fisheries and because protists form the bottom of the ocean food web, the suffering of those calcareous species will affect all the species on up the ocean food chain – all the way up to the top: us. It is estimated that more than one billion of the world’s six billion people depend primarily on the ocean for their protein. A collapse of the ocean food web from ocean acidification could spell disaster for these one billion.

There’s another potential consequence from this chemical problem: more CO2 in the atmosphere. Come again? You read right.

Calcareous protists play a key role in moving dissolved CO2 from surface waters to the deep ocean. When these species die, they sink into the deep ocean taking with them the carbon in their shells and skeletons. This removal allows room for more atmospheric CO2 to settle into the surface ocean. So, damage to species like coccolithophores and foraminifera could slow the rate at which CO2 from fossil-fuel burning finds its way out of the atmosphere.

Not Just Some Theory

That adding dissolved CO2 to the ocean will make the ocean more acidic and destabilize calcium shells and skeletons is pretty, er, basic stuff from a scientific point of view – simple solution chemistry worked out long ago. But scientists have nevertheless been working to confirm that what happens in the lab also happens in the real world.

Late last year, The Green Grok reported on two scientific papers that found increasing levels of acidity in the Southern Ocean and in waters off the coast of Washington.

But what about the effect on the critters themselves? How do we know that ocean acidification will affect them at all? A new paper in Nature Geoscience by Andrew Moy of the Antarctic Climate and Ecosystems Cooperative Research Center in Hobart, Tasmania, and colleagues, provides very convincing evidence of a significant impact.

Moy and his colleagues focused on Globigerina bulloide, a relatively common species of foraminifera that builds its shells out of calcite, the most stable form of calcium carbonate. To identify the effect of ocean acidification on these forams, the scientists compared modern-day shells with those from pre-industrial times. The modern shells were collected from species falling through the ocean column into sediment traps in the Southern Ocean. The pre-industrial samples were gathered from sediment cores pulled out of the Southern Ocean.

The results are striking. The weight of the modern day shells was 30 to 35 percent less than those of their pre-industrial counterparts. But that’s not all. The researchers were able to reconstruct the record of shell weights of G. bulloides over the past 50,000 years. They compared those to the record of CO2 variations over the same period obtained from ice cores. They found a very tight relationship: times of high CO2 had low shell weight and vice versa.

In summary we now have very strong evidence that burning fossil fuels is having a profound impact on the ocean, an impact that may very well be undermining one of our main sources of food.

filed under: carbon dioxide emissions, climate change, faculty, global warming, oceans
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  1. Ken Towe
    Dec 14, 2009

    From Dr. Richard A. Feely (6/5/08): “Scientists have estimated that the pH of our ocean surface waters has already fallen by about 0.11 units from an average of about 8.21 o 8.10 since the beginning of the industrial revolution.” Yet, In the late Eocene and early Oligocene CO2 levels were between 450 and 1500 ppmv and the pH was between 7.5 and 7.8. The data were derived from boron isotope analyses on foraminiferal shells, not unlike those reported to be thinning today at a pH near 8.10. [NATURE, vol. 461, 22 October 2009, p. 1111, Fig. 2] Dr. Brian Huber (Smithsonian foraminiferal specialist) writes: “Climate models for the Turonian require at least 6x present day pCO2 to explain the warm polar temperatures, yet that is a time of high [foraminiferal] speciation and increased shell size and thickness.” Also, in the Cretaceous (Turonian) “The calculated range for the mid-Turonian is 1450–2690 ppmv CO2. This high pCO2 level is similar to or somewhat higher than other estimates for the Cretaceous and in accord with calculated high Turonian temperatures from many studies.” The viewpoint…”That adding dissolved CO2 to the ocean will make the ocean more acidic and destabilize calcium shells and skeletons is pretty, er, basic stuff from a scientific point of view – simple solution chemistry worked out long ago.” Certainly true, but the actual difference in pH seems to be the critical part. The data from the fossil record seem to represent a major disconnect with the modern record.

  2. Bill
    Sep 1, 2009

    Would adding sodium bicarbonate act as a pH buffer and shift the pH higher? I understand NaHCO3 acts as a conjugate base with carbonic acid and acts as a conjugate acid with the carbonate ion, CO3. Is the pH shift affected significantly by temperature as well? Thanks

    • Bill Chameides
      Sep 2, 2009

      Bill, in principle yes, but it’s not a practical solution (no pun intended) — the amount of sodium bicarbonate needed to change the ocean pH would be prohibitive; it would have to counteract the megatons of CO2 we add to the ocean each year. Temperature is a minor factor in ocean pH.

  3. Daniel Wedgewood
    Mar 25, 2009

    Dr. Chameides, Thanks for that information – I had no clue. As with many problems I wonder what technology might help solve the problem (beside the obvious green-house-gas reducing technologies)? Could microbes be engineered to help “fix” that acid-base balance? I wonder because we are already engineering microbes to “eat” oil spills – is it such a big step to solve other problems using the same technology? Dan

    • Bill Chameides
      Mar 27, 2009

      Dan – That is sort of the idea behind iron fertilization – although recent experiments suggest that it might not work ( Here’s the problem with solutions like that: Do we really want to try to fix one environmental problem by perturbing the natural system in ways that have the potential to produce a host of other problems that we have not yet thought of. For example, how could we be sure that those engineered microbes would not cause havoc among ocean communities and fisheries?

      • Daniel Wedgewood
        Mar 27, 2009

        Dr. Chameides, What if careful test and simulations were done as a proof of concept? And, doesn’t the gravity of the situation call for solutions that can work in this political climate? Governments could regulate us to a solution, but since it is very likely they will not, doesn’t that suggest that alternatives must be tried. If they do fail or cause more problems, at least we would have tried something. And, with careful and successful research, might work. Putting faith in politicians seems riskier to me than scientifically engineered microbes (or something else created with sound scientific methods). Dan

        • Bill Chameides
          Mar 30, 2009

          Daniel – some scientists agree that the situation is so dire that we should go forward with these geoengineering approaches. Many, including myself, are very concerned about unintended consequences – do the research, yes, but for now no application. And whatever we do, politicians will have to get involved. Scientists cannot do grand experiments on the environment without government involvement.

          • Daniel Wedgewood
            Mar 30, 2009

            Dr. Chameides – What if the politicians continue to do too little? What are the scientists to do?

            • Bill Chameides
              Apr 7, 2009

              Daniel, In the final analysis scientists can only do the studying part. It is up to politicians and leaders in the private sector to act on the insights gained by scientific studies. Of course, scientists can always decide to switch from the studying to the acting, but then they are not acting as “scientists.” Not that there is anything wrong with that.

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