Volume 14, Number 35: 31 August 2011
In an intriguing new paper, Cameron-Smith et al. (2011) write that "dimethyl sulfide (DMS) is one of the major precursors for aerosols and cloud condensation nuclei in the marine boundary layer over much of the remote ocean," and they state that "models for the distribution of marine DMS have lately been increasing in number and complexity, such that a regional portrait of their evolving climate response is constructible." Thus, they employed the most recent version of the Community Climate System Model (CCSM), described by Collins et al. (2006), to produce the first marine sulfur simulations performed with what they refer to as "the most sophisticated ocean sulfur cycle model yet reported."
In one of their simulations, the atmospheric CO2 concentration was held steady at 355 ppm, while in another it was set at 970 ppm, in order to simulate the climate near the end of the 21st century, as projected by the IPCC (2001) SRES A1F1 emissions scenario. And this latter CO2 concentration and its modeled climatic consequences resulted in the simulation of "rings of high DMS near Antarctica due to the inclusion of a Phaeocystis parameterization," for this unicellular, photosynthetic, eukaryotic alga generates, in the words of the five U.S. scientists, "several times the typical DMSP level (dimethyl sulfoniopropionate, a major DMS precursor) and favors cold water habitat (Matrai and Vernet, 1997)."
Consequently, in the face of the modeled global warming produced by the specified increase in the atmosphere's CO2 concentration, there is a migration of Phaeocystis species towards the cooler waters of higher latitudes; and under these conditions the model employed by Cameron-Smith et al. simulated increases in the "zonal averaged DMS flux to the atmosphere of over 150% in the Southern Ocean," which they say was "due to concurrent sea ice changes and ocean ecosystem composition shifts caused by changes in temperature, mixing, nutrient, and light regimes." And based on other modeling exercises they conducted, they say that the shift in the location of maximum DMS emissions towards colder regions "is usually reinforced with even more sophisticated models."
As for the ultimate climatic implications of the southward shift of the band of significantly-enhanced maximum DMS emissions in the Southern Hemisphere, Cameron-Smith and colleagues say that "in global estimates involving constant upward or downward DMS flux changes, average planetary surface temperatures separate by three or more degrees Celsius," citing the work of Charlson et al. (1987) and Gunson et al. (2006). Thus, it can finally be appreciated that this strong biological response to a CO2-induced impetus for warming, can result in a greatly-strengthened negative regional feedback -- via enhanced regional cloud development -- that results in more incoming solar radiation being reflected back to space with enhanced regional cooling. And we opine that that the resulting DMS-enhanced "thermal insulating" of Antarctica from the rest of the world by this mechanism should significantly reduce the propensity for that continent's ice sheets to lose mass and contribute to sea level rise, even in a world that is experiencing a net warming.
Sherwood, Keith and Craig Idso
References
Cameron-Smith, P., Elliott, S., Maltrud, M., Erickson, D. and Wingenter, O. 2011. Changes in dimethyl sulfide oceanic distribution due to climate change. Geophysical Research Letters 38: 10.1029/2011GL047069.
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.
Collins, W.D., Bitz, C.M., Blackmon, M.L., Bonan, G.B., Bretherton, C.S., Carton, J.A., Chang, P., Doney, S.C., Hack, J.J., Henderson, T.B., Kiehl, J.T., Large, W.G., McKenna, D.S., Santer, B.D. and Smith, R.D. 2006. The Community Climate System Model Version 3 (CCSM3). Journal of Climate 19: 2122-2143.
Gunson, J.R., Spall, S.A., Anderson, T.R., Jones, A., Totterdell, I.J. and Woodage, M.J. 2006. Climate sensitivity to ocean dimethylsulphide emissions. Geophysical Research Letters 33: 10.1029/2005GL024982.
Matrai, P. and Vernet, M. 1997. Dynamics of the vernal bloom in the marginal ice zone of the Barents Sea: Dimethyl sulfide and dimethylsulfoniopropionate budgets. Journal of Geophysical Research 102: 22,965-22,979.