GCRA  OVERVIEW  FAQ  NEWS  ARTICLES  PHOTOS  REEF ISSUES  RESTORATION  PAPERS  LINKS 

February 26 2009

 T. J. GOREAU COMMENTS ON “OCEAN ACIDIFICATION”

by Eugene H. Buck & Peter Folger

Congressional Research Service Report for Congress R40143

 This is generally a good summary, but it needs correction in a number of places.

 One essential missing point that should be pointed out in the introduction is that despite the recent publicity about ocean acidification as an “unexpected” “shocking” “new” problem, this is completely incorrect. It has been known since the start of marine chemistry over a hundred years ago that carbon dioxide was the major acid gas in the atmosphere, and that any increase would cause the ocean to become more acidic. This can be found in any marine chemistry textbook. More than 30 years ago we would make Harvard undergraduate geochemistry students routinely calculate the equilibrium decrease in ocean pH for doubling of atmospheric CO2 as a homework exercise problem.

 A further missing point is that while it is pointed out that cold polar waters dissolve more CO2 from the atmosphere, it is not pointed out that warm tropical waters have excess CO2 and release CO2 to the atmosphere, and will continue to do so as CO2 rises as this is a consequence of the temperature difference between the poles and the equator. These global CO2 flux patterns have been documented worldwide for decades through the masterful work of Taro Takahashi and his many colleagues, but this is not cited.

 Specific comments follow:

 Page 1, Paragraph 2, last sentence. This sentence “As long as atmospheric CO2 continues to increase, many scientists expect the oceans to continue to become more acidic” (my italics) is much too weak. This makes it appear as an unsettled point that is merely a matter of opinion, like saying that “some scientists expect the earth to warm up if CO2 increases” creates a false sense of doubt that should not in any way encouraged. But in fact both are the inescapable result of fundamental physical laws, not hypotheses that need to proven, or over which there is any scientific controversy at all. Ocean acidification is the inevitable result of Henry’s Law of gas solubility and the Law of Mass Balance for ionization of carbonic acid, just as global warming is the unavoidable result of Lambert’s Law when CO2 increases. These increases of ocean acidity and temperature are the results of physical laws that are as ironclad as the law of gravity saying an apple will fall toward the earth: there are no exceptions! Please eliminate the word “many”.

 P. 1, Pa. 3, last line. Change “may” to “will”.

 P. 1, last lines, P. 2 first lines. This wording implies that the factor affecting the time constant of acidification is the rate of dissolution and transport of CO2 within the ocean to reach equilibrium, but it ignores the much larger internal reactions that affect CO2 and hence the equilibration time constant, such as photosynthesis and respiration (OK, we can finesse these two by assuming they balance, but that is never really true in the short term), and far more importantly the rate of dissolution of sedimentary and suspended limestone in the deep sea, which absolutely cannot be neglected, and is the key in determining the long term pH change.

 P. 2 last full paragraph. This is based on a naïve interpretation by chemists, which ignores the biology, and affects the interpretation of all that follows. In fact organisms are not passively dependent on the chemistry of the ocean for their ability to grow limestone shells because they actively concentrate calcium by enzymatic pumps and they use a series of enzymes, particularly carbonic anhydrase, to make carbonate ion internally from bicarbonate. As a result the internal composition is very distinct from the outside water, and organisms can calcify in acidic waters. These mechanisms were worked out by the late Thomas F. Goreau more than 50 years ago.

 P. 3, last paragraph. The discussion about corals is not correct. The internal acidity and CO2 content of coral tissues undergoes very large daily cycles that are unrelated to the external ocean chemistry. In the daytime CO2 falls and pH rises as zooxanthellae photosynthesize, and at nighttime CO2 rises and pH falls due to respiration. The role of increasing external CO2 is not known, but certainly minor compared to these large internal cycles. The paper cited is not about this at all, but about a fungus isolated from diseased corals.

 P. 4, First full paragraph. There have been large and rapid changes in the compensation depth through geological time, and these are very important for determining the rate at which ocean acid is neutralized by dissolving limestone sediments. But most of these were caused by changes in ocean deep circulation rates, and if this is happening at present this could have very large impacts on ocean pH, probably larger than rising atmospheric CO2.

 P. 4, Last full paragraph. The paper cited on declining coral growth in the Great Barrier Reef attributed it to increasing ocean acidification, but completely failed to mention coral bleaching, that these corals had repeatedly bleached due to high temperatures in the last two decades, and that bleached corals completely stop growing for at least a year. The effect of acidification per se was almost certainly minor.

 P. 5, first paragraph. A great paper by M. Fine et al should be cited, in which corals were grown in water so acidic that their skeletons totally dissolved, and they were not harmed. When they were later put back into alkaline water they grew back their skeletons. Therefore acidification may be a threat to coral reefs as a geological feature on the time scale of centuries, but it won’t kill corals. On the other hand a 1 degree C rise in temperature bleaches or kills corals, and bleaching is accurately predictable from sea surface temperature data alone (Goreau & Hayes, 1994).

 P. 5, first full paragraph. The suggestion that iron fertilization could reduce global surface ocean acidity is seriously flawed. First only a small part of the ocean is iron limited, most is limited by lack of nitrogen and phosphorus. Second only a very tiny fraction of carbon taken up by phytoplankton in iron limited areas that are fertilized is in fact buried, the vast majority rots or is eaten, and returned to the ocean and atmosphere on a very short time scale. The idea that limestone could be added to the ocean ignores the vast amount needed and the fact that anyway limestone is abundant in almost all shallow ocean sediments. These points greatly strengthen the conclusion at the end of the paragraph, that only reductions in atmospheric CO2 concentrations can reduce the rate of acidification and its consequences.

 Last two sections, P. 5 – P. 7. There is no doubt that more research is a good thing, but we already know that ocean acidification is a potentially serious problem, primarily for cold water and deep ocean ecosystems, will last for thousands of years, and only reducing atmospheric CO2 now can prevent them. There is a serious risk that scientists and government agencies will use acidification as an excuse to do get funding for research to “find out if there is a problem”, and that this will once again be used as an excuse to delay action on a problem whose solutions are well known, even if all the details remain to be worked out. In that sense this could be a repeat of the irresponsible way in which the impacts of temperature on coral bleaching were ignored for decades, allowing most corals to die. As far as corals go, high temperature is an immediate threat, acidification is a remote future threat. CO2 must be reduced to solve the first problem, thereby automatically solving the second. Giving priority to the second is a red herring that guarantees corals will be killed on a very short time scale.

 Thomas J. Goreau, PhD, President, Global Coral Reef Alliance