Will Ocean Acidification -- If It Occurs -- Affect Marine Microbes?

Writing as background for their study, authors Joint et al. (2011) say "the pH of the surface ocean is changing as a result of increases in atmospheric carbon dioxide," and they state that "there are concerns about potential impacts of lower pH and associated alterations in seawater carbonate chemistry on the biogeochemical processes in the ocean," noting that "it is important to place these changes within the context of pH in the present-day ocean." Joint et al. continue by briefly reviewing what is known about the latter subject and present their thoughts about it in a Perspectives article.

According to the three researchers, "marine and freshwater assemblages have always experienced variable pH conditions." They note, for example, that "phytoplankton blooms can rapidly reduce pCO₂, with a concomitant increase in pH," which subsequently declines as the blooms die out, demonstrating that "pH is naturally variable and that marine organisms -- particularly microbes -- must already be capable of adapting to rapid and sometimes large changes in pH." On another time scale, they note that oceanic pH can change by up to 0.06 pH unit during the year even in the oligotrophic Central Pacific, which does not experience the dramatic phytoplankton blooms of temperate oceans."

In the case of freshwater ecosystems, Joint et al. report that "Maberly (1996) showed that diel variations in a lake can be as much as 2-3 pH units," and that "Talling (2006) showed that in some English lakes, pH could change by >2.5 pH units over a depth of only 14 m," while noting that "phytoplankton, bacteria, archaea and metazoans are all present in lakes, and appear to be able to accommodate large daily and seasonal changes in pH."

Given the above facts, the three researchers conclude that "perhaps the most appropriate null hypothesis to test is that marine microbes possess the flexibility to accommodate pH change and there will be no catastrophic changes in marine biogeochemical processes that are driven by phytoplankton, bacteria and archaea."

Additional References
Maberly, S.C. 1996. Diel, episodic and seasonal changes in pH and concentrations of inorganic carbon in a productive lake. Freshwater Biology 35: 579-598.

Talling, J.F. 2006. Interrelated seasonal shifts in acid-base and oxidation-reduction systems that determine chemical stratification in three dissimilar English lake basins. Hydrobiologia 568: 275-286.