Karen M. Shell     


Effect of absorption of solar radiation by phytoplankton on the atmosphere

Relevant Papers:

Shell, K. M., R. Frouin, S. Nakamoto, and R. C. J. Somerville, Atmospheric response to solar radiation absorbed by phytoplankton, J. Geophys. Res., 108(D15), 4445, doi:10.1029/2003JD003440, 2003. (**)

Miller, A. J., M. A. Alexander, G. J. Boer, F. Chai, K. Denman, D. J. Erickson, R. Frouin, A. J. Gabric, E. A. Laws, M. R. Lewis, Z. Liu, R. Murtugudde, S. Nakamoto, D. J. Neilson, J. R. Norris, J. C. Ohlmann, R. I. Perry, N. Schneider, K. M. Shell, and A. Timmerman, 2003: Potential feedbacks between Pacific Ocean ecosystems and interdecadal climate variations. Bull. Amer. Meteor. Soc., 84, 617-633. (*)

Figure from Shell et al. (2003). Monthly average (a) global, (b) Northern Hemisphere, and (c) Southern Hemisphere temperature differences (phytoplankton run minus control run) between 60°S and 60° N for SST (squares) and lowest layer atmospheric temperature of all land points (upside-down triangles), ocean points (asterisks), and land points (triangles). The vertical lines indicate the standard error of the difference.

Phytoplankton alter the absorption of solar radiation, affecting upper ocean temperature and circulation. These changes, in turn, influence the atmosphere through modification of the sea surface temperature (SST). To investigate the effects of the present-day phytoplankton concentration on the atmosphere, Robert Frouin, Sho Nakamoto, Richard Somerville, and I forced an atmospheric general circulation model (CCM3) with SST changes due to phytoplankton from an earlier ocean GCM experiment with space- and time-varying phytoplankton abundances from Coastal Zone Color Scanner data.

Our results indicate that phytoplankton amplify the seasonal cycle of the lowest atmospheric layer temperature by about 0.3 K, but the amplification may reach over 1 K locally. The surface warming in the summer is marginally larger than the cooling in the winter, so that on average annually and globally, phytoplankton warm the lowest layer by about 0.05 K. Over the ocean the surface air temperature changes closely follow the SST changes. Significant, often amplified, temperature changes also occur over land. The climatic effect of phytoplankton extends throughout the troposphere, especially in middle latitudes where increased subsidence during summer traps heat. The amplification of the seasonal cycle of air temperature strengthens tropical convection in the summer hemisphere. In the eastern tropical Pacific Ocean a decreased SST strengthens the Walker circulation and weakens the Hadley circulation. These significant atmospheric changes indicate that the radiative effects of phytoplankton should not be overlooked in studies of climate change.

Last updated Oct. 20, 2006