Ocean Acidification

"However, the role of acidification in this decline is far from settled. In the laboratory, Alina Szmant, a coral physiological ecologist at the University of North Carolina, Wilmington, and her colleagues found that neither low pH nor a lowered calcium carbonate concentration (which results from increased acidity and is considered key to calcification) slowed coral growth. Instead, calcium bicarbonate proved key, her team reported at ICRS. She faults previous lab studies because they used hydrochloric acid, not carbon dioxide, to lower the pH of the water in the calcification studies. Hydrochloric acid and carbon dioxide have different effects on seawater chemistry and bicarbonate concentration, she says. Her conclusion: "It's not clear that carbon dioxide enrichment will have negative effects on calcification rates.""

On the other hand, Glenn De'ath (what a name!) has done studies showing that corals are slowing growth:
A large-scale study in Australia's Great Barrier Reef has revealed that the rate at which corals absorb calcium from seawater to calcify their hard skeletons has declined precipitously in the past 20 years, slowing coral growth. The report, on page 116, provides empirical data that fuels concerns that increased carbon dioxide in the air is putting these diverse marine ecosystems at risk (Science, 4 May 2007, p. 678).


So, ocean acidification: this has become a favorite argument at WattsUp and other skeptic places:

1) "acidification" _is_ the appropriate term for something become more acidic, regardless of whether the pH is below or above 7. "today was 2 degrees warmer than yesterday" regardless of whether yesterday was -30 or 80. "becoming less alkaline" would also be correct, but is kind of awkward. "neutralization" is less awkward, but I would argue less correct than "acidification" because there is an end state of pH 7 implied by neutralization. (those who don't believe me, look up the term "urine alkalinization" in which raising urine's pH to 6.5 is called alkalinization).

2) as the oceans warm, CO2 becomes less soluble: all other things being equal, warming would result in natural alkanization. However, Henry's Law states than in equilibrium, ocean CO2 is proportional to atmospheric CO2 over Henry's coefficient. The coefficient hasn't increased nearly as much as atmospheric CO2 has, so the ocean is still a sink. (see the carbon cycle argument in this blog).

3) there are many examples in biochemistry and biology of pH sensitive organisms. The argument between the Szmants and the De'aths basically comes down to whether there are enough organisms sensitive to the rate of change we expect over the next decades to lead to significant ecosystem degradation. And even if acidification by itself doesn't reach a tipping point, there is still a question of whether it will add on top of other stressors like temperature changes and anoxia events and overfishing... I think the magnitude of this additional stress is still uncertain, but my guess is that it is large enough to be significant. More Szmant type studies would calm me down, though.