How does rising atmospheric CO2 affect marine organisms?

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Oceanic Dimethylsulfide Production in a CO2-Enriched and Warmer World
Kim, J.-M., Lee, K., Yang, E.J., Shin, K., Noh, J.H., Park, K.-T., Hyun, B., Jeong, H.-J., Kim, J.-H., Kim, K.Y., Kim, M., Kim, H.-C., Jang, P.-G. and Jang, M.-C. 2010. Enhanced production of oceanic dimethylsulfide resulting from CO2-induced grazing activity in a high CO2 world. Environmental Science & Technology: 10.1021/es102028k.

The authors write that dimethylsulfide or DMS is "a semivolatile organic sulfur compound that represents 95% of the natural marine flux of sulfur gases to the atmosphere (Bates et al., 1992; Liss et al., 1997)," and they say that it "may be oxidized to form non sea-salt sulfate aerosols, which are known to act as cloud condensation nuclei and thereby exert a cooling effect by absorbing or scattering solar radiation," citing Charlson et al. (1987), who first described the intriguing and important chain of events. They also say that "DMS is generated by intracellular or extracellular enzymatic cleavage of DMSP [dimethylsulfoniopropionate] by DMSP-lyase, which is synthesized by algae and bacteria, following DMSP secretion from producer cells or release following autolysis or viral attack," while noting that "grazing activity can also result in DMSP conversion to DMS if DMSP and DMSP-lyase are physically mixed following grazing," citing (Stefels et al., 2007; Wolfe and Steinke, 1996)."

What was done
Working in the coastal waters of Korea from 21 November to 11 December 2008, the fourteen Korean scientists utilized 2400-liter mesocosm enclosures to simulate, in triplicate, three sets of environmental conditions -- an ambient control (~400 ppm CO2 and ambient temperature), an acidification treatment (~900 ppm CO2 and ambient temperature), and a greenhouse treatment (~900 ppm CO2 and ~3C warmer-than-ambient temperature) -- and within these mesocosms they initiated phytoplankton blooms by adding equal quantities of nutrients to each mesocosm on day 0, while for 20 days thereafter they measured numerous pertinent parameters within each mesocosm.

What was learned
Kim et al. determined that "the total accumulated DMS concentrations (integrated over the experimental period) in the acidification and greenhouse mesocosms were approximately 80% and 60% higher than the values measured in the control mesocosms, respectively." And they say they attribute these results to the fact that, in their experiment, (1) "autotrophic nanoflagellates (which are known to be significant DMSP producers) showed increased growth in response to elevated CO2," and that (2) "grazing rates [of microzooplankton] were significantly higher in the treatment mesocosms than in the control mesocosms."

What it means
In the concluding paragraph of their paper, Kim et al. write that "in the context of global environmental change, the key implication of our results is that DMS production resulting from CO2-induced grazing activity may increase under future high CO2 conditions," and, therefore, they conclude that "DMS production in the ocean may act to counter the effects of global warming in the future."

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.

Charlson, R.J., Lovelock, J.E., Andreae, M.O. and Warren, S.G. 1987. Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate. Nature 326: 655-661.

Liss, P.S., Hatton, A.D., Malin, G., Nightingale, P.D. and Turner, S.M. 1997. Marine sulphur emissions. Philosophical Transactions of the Royal Society London B 352: 159-169.

Stefels, J., Steinke, M., Turner, S., Malin, G. and Belviso, S. 2007. Environmental constraints on the production and removal of the climatically active gas dimethylsulphide (DMS) and implications for ecosystem modeling. Biogeochemistry 83: 245-275.

Wolfe, G.V. and Steinke, M. 1996. Grazing-activated production of dimethyl sulfide (DMS) by two clones of Emiliania huxleyi. Limnology and Oceanography 41: 1151-1160.

Reviewed 3 November 2010