What was done
As part of the Third Pelagic Ecosystem CO2 Enrichment Study, the authors investigated the effects of atmospheric CO2 enrichment on marine microorganisms within nine marine mesocosms maintained within 2-m-diameter polyethylene bags submerged to a depth of 10 m in a fjord at the Large-Scale Facilities of the Biological Station of the University of Bergen in Espegrend, Norway. Three of these mesocosms were maintained at ambient levels of CO2 (~375 ppm or base CO2), three were maintained at levels expected to prevail at the end of the current century (760 ppm or 2xCO2), and three were maintained at levels predicted for the middle of the next century (1150 ppm or 3xCO2). During the 25 days of their experiment, the 12 researchers followed the development and subsequent decline of an induced bloom of the coccolithophorid Emiliania huxleyi, carefully measuring several physical, chemical and biological parameters along the way.

What was learned
Wingenter et al. determined that "dimethyl sulfide (DMS) production followed the development and decline of the phytoplankton bloom," and that "maximum DMS concentrations coincided with the peak in chlorophyll-a concentrations in the present day CO2 treatment, but were delayed by 1-3 days relative to chlorophyll-a in the double and triple CO2 treatments," noting additionally that "DMS was 26% and 18% higher in the 2x and 3xCO2 mesocosms, respectively (days 0-17)." The iodocarbon chloroiodomethane (CH2CII), on the other hand, had its peak concentration about 6-10 days after the chlorophyll-a maximum; but its estimated abundance was 46% higher in the 2xCO2 mesocosms and 131% higher in the 3xCO2 mesocosms.

What it means
The international team of scientists concluded that "the differences in DMS and CH2CII concentrations may be viewed as a result of changes to the ecosystems as a whole brought on by the CO2 perturbations." And because emissions of both DMS (Bates et al., 1992; Clarke et al., 1998) and various iodocarbons (O'Dowd et al., 2002; Jimenez et al., 2003) typically lead to an enhancement of cloud condensation nuclei in the marine atmosphere, the CO2-induced stimulations of the marine emissions of these two substances provide a natural brake on the tendency for global warming to occur as a consequence of any forcing, as they lead to the creation of more-highly-reflective clouds over greater areas of the world's oceans. Consequently, as Wingenter et al. describe it, "these processes may help contribute to the homeostasis of the planet."

For more on these topics, see our review of Smythe-Wright et al. (2006) and the many analogous items we have archived under the heading of Dimethyl sulfide in our Subject Index.

References
Bates, T.S., Lamb, B.K., Guenther, A., Dignon, J. and Stoiber, R.E. 1992. Sulfur emissions to the atmosphere from natural sources. Journal of Atmospheric Chemistry 14: 315-337.

Clarke, A.D. et al. 1998. Particle nucleation in the tropical boundary later and its coupling to marine sulfur sources. Science 282: 89-92.

Jimenez, J.L., Bahreini, R., Cocker III, D.R., Zhuang, H., Varutbangkul, V., Flagan, R.C., Seinfeld, J.H., O'Dowd, C.D. and Hoffmann, T. 2003. New particle formation from photooxidation of diiodomethane (CH2I2). Journal of Geophysical Research 108: 10.1029/2002JD002452.

O'Dowd, C.D., Jimenez, J.L., Bahreini, R., Flagan, R.C., Seinfeld, J.H., Hameri, K., Pirjola, L., Kulmala, M., Jennings, S.G. and Hoffmann, T. 2002. Marine aerosol formation from biogenic iodine emissions. Nature 417: 632-636.

Smythe-Wright, D., Boswell, S.M., Breithaupt, P., Davidson, R.D., Dimmer, C.H. and Eiras Diaz, L.B. 2006. Methyl iodide production in the ocean: Implications for climate change. Global Biogeochemical Cycles 20: 10.1029/2005GB002642.