Unexpected consequences of increasing CO ₂ and ocean acidity on marine production of DMS and CH ₂ ClI: Potential climate impacts

Increasing atmospheric mixing ratios of CO 2 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 CO 2 perturbation experiments. Marine microorganisms are known to consume and produce climate‐relevant organic gases. Concentrations of (CH 3 ) 2 S (DMS) and CH 2 ClI were quantified during the Third Pelagic Ecosystem CO 2 Enrichment Study. Positive feedbacks were observed between control mesocosms and those simulating future CO 2 . Dimethyl sulfide was 26% (±10%) greater than the controls in the 2x ambient CO 2 treatments, and 18% (±10%) higher in the 3xCO 2 mesocosms. For CH 2 ClI the 2xCO 2 treatments were 46% (±4%) greater than the controls and the 3xCO 2 mesocosms were 131% (±11%) higher. These processes may help contribute to the homeostasis of the planet.