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Biogenic Methyl Iodide Production in the World's Oceans
Reference
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.

What was done
The authors measured trace gas and pigment concentrations in seawater, while identifying and enumerating picophytoprokaryotes during two cruises in the Atlantic Ocean and one in the Indian Ocean, "focusing on methyl iodide production and the importance of a biologically related source."

What was learned
Smythe-Wright et al. report finding methyl iodide concentrations of up to 45 pmol L-1 in the top 150 m of the oceanic water column that "correlate well with the abundance of Prochlorococcus," which "can account for >80% of the variability in the methyl iodide concentrations," and they add that they "have confirmed the release of methyl iodide by this species in laboratory culture experiments."

Extrapolating their findings to the globe as a whole, the researchers "estimate the global ocean flux of iodine [I] to the marine boundary layer from this single source to be 5.3 x 1011 g I year-1," which they say "is a large fraction of the total estimated global flux of iodine (1011-1012 g I year-1) to the atmosphere."

What it means
These findings are extremely important, because volatile iodinated compounds, in Smythe-Wright et al.'s words, "play a part in the formation of new particles and cloud condensation nuclei (CCNs)," and especially because "an increase in the production of iodocompounds and the subsequent production of CCNs would potentially result in a net cooling of the earth system and hence in a negative climate feedback mechanism, mitigating global warming."

More specifically, the six scientists say that "as ocean waters become warmer and more stratified, nutrient concentrations will fall and there will likely be a regime shift away from microalgae toward Prochlorococcus," which "implies that as global warming takes hold there will be a concomitant increase in the abundance of Prochlorococcus." In addition, they suggest that "colonization within the <50 latitude band will result in a ~15% increase in the release of iodine to the atmosphere," with consequent "important implications for global climate change," which, as they note, result in a mitigation of global warming.

Reviewed 22 November 2006