Ocean Acidification and Marine Trace Gases

While the lion’s share of studies on the direct impacts of increased uptake of carbon dioxide in the world’s oceans have focused upon potential acidification effects on marine organisms, especially calcifiers, there is growing evidence that this uptake may also feed into changes in the Earth’s future climate. A recent study focuses on some of the most important potential biogeochemical processes, Frances E. Hopkins, et al., Ocean Acidification and Marine Trace Gas Emissions, 107 PNAS 760-765 (2010) (subscription required). The study used a mesocosm carbon dioxide perturbation experiment in a Norwegian, examining a transition from present day concentrations of 38p ppmv to a projection of 750 ppmv in the year 2100.

Among the key take-aways of the study:

  1. A 57%  reduction in dimethylsulfide (DMS) was observed under high carbon dioxide for the bloom period of the experiment; by the end of the experiment DMS was 3x higher under present day carbon dioxide conditions than under the high carbon dioxide treatment. DMS produces particles that interact with incoming solar radiation and affects planetary albedo, potentially exerting a very potent positive feedback.  The projected decrease in DMS “could result in enough net cloud radiative forcing to increase surface air temperature by 1.6ºC.” However, the results differ from a 2005 mesocosm experiment which showed only small differences in DMS between elevated and ambient carbon dioxide treatments. Differences in the planktonic communities in the two respective experiments may explain the different results;
  2. Lower levels of pH associated with higher ocean carbon dioxide concentrations could result in substantial decreases of iodocarbon gases and increases of bromocarbon gases. While the study did not assess the implications, it explains that iodine oxides contribute to particle formation and production of cloud condensation nuclei, with potentially significant effects on radiative forcing. Moreover, longer-lived halogen species are involved in natural regulation of the stratospheric ozone layer.

While the authors caution that much more research in this context is necessary, this would be an excellent student reading (graduate level course) to demonstrate the complexity of potential feedback mechanisms and the ever-growing potential perils that ocean acidification and rising levels of carbon dioxide in the world’s may pose in this century and beyond.

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