Ocean acidification and marine trace gas emissions

The oceanic uptake of man-made CO2 emissions is resulting in a measureable decrease in the pH of the surface oceans, a process which is predicted to have severe consequences for marine biological and biogeochemical processes [Caldeira K, Wickett ME (2003) Nature 425:365; The Royal Society (2005) Policy Document 12/05 (Royal Society, London)]. Here, we describe results showing how a doubling of current atmospheric CO2 affects the production of a suite of atmospherically important marine trace gases. Two CO2 treatments were used during a mesocosm CO2 perturbation experiment in a Norwegian fjord (present day: similar to 380 ppmv and year 2100: similar to 750 ppmv), and phytoplankton blooms were stimulated by the addition of nutrients. Seawater trace gas concentrations were monitored over the growth and decline of the blooms, revealing that concentrations of methyl iodide and dimethylsulfide were significantly reduced under high CO2. Additionally, large reductions in concentrations of other iodo-carbons were observed. The response of bromocarbons to high CO2 was less clear cut. Further research is now required to understand how ocean acidification might impact on global marine trace gas fluxes and how these impacts might feed through to changes in the earth's future climate and atmospheric chemistry.