The oceans’ acid test: can our reefs be saved? – a note from Frontiers in Ecology and the Environment

5 thoughts on “The oceans’ acid test: can our reefs be saved? – a note from Frontiers in Ecology and the Environment”

  1. I’m still looking for some serious discussion on the chermothermodynamics of “ocean acidification” and corals

    Steve Short launched this broadside earlier in the year.

    ” ……

    Aragonite (the form of calcium carbonate secreted by corals) and calcite (the form of calcium carbonate secreted by calcareous forams i.e. the phytoplankton known as cocolithophores) CANNOT begin to dissolve unless they are thermodynamically permitted to do so i.e. their Saturation Indices (SIs) must be less than zero.
    For an ocean fully equilibrated with the atmosphere, it would require an increase in the partial pressure (concentration) of CO2 in the atmosphere 6.4 times the current level to 2455 ppmv (presently 384 ppmv) to drive the SI of aragonite down from its present +0.61 to zero.
    pH of the seawater would then be 7.52 (expressed at 25 C, the standard temperature for expressing pHs).
    For an ocean fully equilibrated with the atmosphere, it would require an 8.8 times increase in the partial pressure of CO2 in the atmosphere to a level of 3388 ppmv ppm (presently 384 ppmv) to drive the SI of calcite down from its present +0.73 to zero.
    pH of the seawater would then be 7.39.
    These values are based on over 200 years of the study of (and parameter measurement in) solution thermodynamics and can be easily obtained in about 15 minutes using any standard geochemical model such as USGS PHREEQC.
    The established paleoclimatic literature shows quite clearly that the occurrences of corals and calcareous phytoplankton in the geological record over the last several hundreds of million years are fully consistent with the above thermodynamic facts.
    Thus the modern level of CO2 in the atmosphere of 384 ppmv would have to double 2 – 3 times before corals and calcareous plankton would begin to disappear.
    Until we approached such a condition any field observations are highly likely to be instances of natural, complex ‘noise’ restricted to specific species or other local factors.
    Posted by: Steve Short at July 29, 2008 04:23 PM
    Yeah, thanks Steve, but I read that post before.
    Three points:
    1. it does not answer my earlier point that much of what I read about tests on calcifying creatures says it makes it hard for them to build and maintain their shells. (Less carbonate available, I believe). This is a different issue from what your post is about, is it not?
    2. In any event, your post does match up with what the Royal Society paper on ocean acidification indicates about saturation levels for calcite and aragonite. They talk in terms of undersaturation; not zero saturation.
    I haven’t quite worked out all of this to my satisfaction yet, but I find it hard to believe that you alone have discovered a fatal flaw in their chemistry. Or indeed, why you have become world famous for pointing out the alleged flaw.
    3. One of the creatures that they have concerns about in acidified oceans are pterpods. This quote is from a NOAA website http://tinyurl.com/6oqxzg :
    “For organisms with external calcium carbonate skeletons, such as corals and pteropods, the consequences can be very negative if the oceans become undersaturated (corrosive) with respect to aragonite, a form of calcium carbonate. It has been demonstrated that pteropods, a planktonic mollusk, may not be able to maintain their shells in undersaturated waters. In some studies, live pteropods were subjected to waters that are undersaturated with respect to aragonite and their shells begin to dissolve within 48 hours (Feely et al., 2004; Orr et al 2005 ).”
    I believe that the study was done using water at a pH and undersaturation levels based on predictions for polar ocean water in 2100.
    If they are wrong, where did they go wrong? Again, couldn’t you be famous by pointing out why how this real life experiment went disastrously wrong?
    4. You have recently made a point in a post about how could it be that higher atmospheric CO2 in earth’s past has allowed coral to grow. The Royal Society paper dealt with this: it’s because the oceans natural pH buffering system can cope with slow increases of CO2. Industrialisation, by contrast, is leading to a rapid (in geological terms) increase in atmospheric CO2, and it will take tens of thousands of years to reduce to get the pH back to pre-industrial levels.
    That last point in particular makes me think you have not seriously looked at ocean acidification at all.
    Posted by: steven watkinson at July 29, 2008 05:35 PM
    Sorry, a few typos in the last post. Of course I meant “why you have not become famous…etc”.
    Oh, and you can stop the condescending tone too. I have read your posts; you might actually try addressing my counterarguments if you want to prove me (or, more importantly, hundred of ocean scientists) wrong.
    Posted by: steven watkinson at July 29, 2008 05:47 PM
    The point is that corals do grow happily right up to about an atmospheric CO2 concentration of around 2500 ppmv and calcareous phytoplankton (foraminifera) do grow happily right up to about an atmospheric CO2 concentration of around 3400 ppmv. The SI has to go under zero for calcite and aragonite to begin to dissolve. This implies an absolute requirement for the near-surface layers of the ocean to be in equilibrium with an atmosphere above them which contains CO2 at a certain, mathematically determinable concentration.
    Anything else is science faction (actually science fantasy).
    Wakey, wakey – this is precisely why the measurement of O18, strontium, magnesium etc in fossil corals and the skeletons of foraminifera are standard and long-used tool in paleoclimatic studies going back 300 plus million years.
    I give up. Basically, you are clearly an absolute idiot. You have no understanding of chemistry at all or any capacity or desire to understand. You do not deserve the courtesy I extended to you. Gawd save us from these arrogant post-modernist idiots and their paper-thin educations. In a word – eff orf.
    Posted by: Steve Short at July 29, 2008 05:56 PM

    ……..”

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  2. In short – Steve Short is saying that ocean acidification causing dissolution of marine organism shells is chemo-thermodynamically impossible at the CO2 levels currently and those likely to be foreseen in the future. And he has challenged anyone on the chemistry of this.

    i.e. ocean acidification is bunk.

    Read his first few paragraphs.

    So I’m looking for a rebuttal. Surprised we have no takers ! Ove !!!

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  3. Luke, Steve Short seems to think coral reefs are just a hunk of inorganic rock in a test tube. It is not simply the case that we’ll be looking at corals dissolving like an aspirin dropped into a glass of water. A critical component that he misses is that even small reductions in calcification rates can cause major problems for coral reefs in the real world where growth rates are finely balanced with removal processes. As NOAA states at the link I gave you:

    “The production rate of CaCO3 must exceed that of the removal processes (dissolution, storm export, and bioerosion) in order for the reef to grow (termed ‘reef accretion’). Studies of CaCO3 budgets on coral reefs suggest that these building and erosive processes are nearly balanced at most modern reefs, and net reef accretion is small. … Thus, a primary threat of ocean acidification is the potential to compromise the ability for reefs to maintain a positive net accretion, thereby resulting in the loss of critical habitat and coastal protection.”

    “The effects of ocean acidification on calcification rate appears not to be directly related to changes in pH per se, but instead to corresponding changes in the degree to which seawater is supersaturated with respect to the carbonate minerals (e.g., aragonite) [Langdon and Atkinson, 2005]. A change in carbonate ion concentration results in a proportional change in Ωarg such that as ocean acidification continues, the surface ocean Ωarg-values will decline. As the saturation state declines, it is harder for marine calcifiers to precipitate the calcium carbonate they need to build their skeletons (see figure below). By the year 2065, rates could decline 60 ± 20% relative to preindustrial levels.”

    See http://coralreefwatch.noaa.gov/satellite/oa/description/oaps_intro_aragonite_ss.html

    If you want something more detailed than this, have a look at Langdon C. and M. J. Atkinson (2005), Effect of elevated pCO2 on photosynthesis and calcification of corals and interactions with seasonal change in temperature/irradiance and nutrient enrichment, Journal of Geophysical Research, 110(C09S07).

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