Unexpected consequences of increasing CO2 and ocean acidity on marine production of DMS and CH2ClI: potential climate impacts

Increasing atmospheric mixing ratios of CO₂ have already lowered surface ocean pH by 0.1 units compared to preindustrial values and pH is expected to decrease an additional 0.3 units by the end of this century. Pronounced physiological changes in some phytoplankton have been observed during previous CO₂ perturbation experiments. Marine microorganisms are known to consume and produce climate-relevant organic gases. Concentrations of (CH₃)₂S (DMS) and CH₂ClI were quantified during the Third Pelagic Ecosystem CO₂ Enrichment Study. Positive feedbacks were observed between control mesocosms and those simulating future CO₂. Dimethyl sulfide was 26% (±10%) greater than the controls in the 2x ambient CO₂ treatments, and 18% (±10%) higher in the 3xCO₂ mesocosms. For CH₂ClI the 2xCO₂ treatments were 46% (±4%) greater than the controls and the 3xCO₂ mesocosms were 131% (±11%) higher. These processes may help contribute to the homeostasis of the planet.