The effects of elevated CO2 and ocean acidification on the production of marine biogenic trace gases

The human-induced increases in atmospheric carbon dioxide since the beginning of the industrial revolution have led to increasing oceanic carbon uptake and changes in seawater carbonate chemistry, resulting in lowering of surface water pH. To date, surface ocean acidity has increased by 30% compared with pre-industrial times. The aim of this study was to investigate the relationship between increasing pCO2, decreasing pH and changes in volatile dimethylsulphide (DMS) and halocarbon concentrations, through 70,000 litre, high pCO2 mesocosm experiments and laboratory culture studies. DMS is a climatically important trace gas produced by marine algae: it transfers sulphur into the atmosphere and is a major influence on biogeochemical climate feedbacks. Halocarbons are also important biogenic trace gases which undergo atmospheric photochemical degradation, releasing halide radicals to participate in atmospheric ozone cycling, and transfer halogens from sea to land. Evidence is presented from a Norwegian coastal study which showed a 60% DMS, 30% DMSP and 40% iodocarbon reduction in high pCO2 mesocosms, and in the Baltic Sea, known for its low-salinity, cyanobacterial dominated community, where DMS concentrations showed an 80% reduction under high pCO2 but halocarbon concentrations were unaffected. No decrease in DMS or DMSP concentrations were identified in high pCO2 laboratory cultures of the DMSproducing species Emiliania huxleyi RCC1229, and halocarbons were undetectable. Changes in trace gas concentrations may arise due to pH effects on the interactions between microbial producers and consumers. Other effects may arise from cell biochemistry due to long-term adaptation to increased ρCO2 and reduced pH on the enzymatic activity production of the compounds. Further studies should determine the nature of the pCO2 and pH effect on bacterial interactions with DMS, DMSP and halocarbon production and breakdown. There should also be attention given to the DMS source in the cyanobacterial-dominated community of the Baltic Sea.

Webb A., 2015. The effects of elevated CO2 and ocean acidification on the production of marine biogenic trace gase. PhD thesis, University of East Anglia, 424 pp. Thesis.


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