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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. D15, 4445, doi:10.1029/2003JD003440, 2003

Atmospheric response to solar radiation absorbed by phytoplankton

K. M. Shell

Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA


R. Frouin

Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA


S. Nakamoto

Advanced Earth Science and Technology Organization, Tokyo, Japan


R. C. J. Somerville

Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA


Abstract

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, an atmospheric general circulation model was forced by SST changes due to phytoplankton. The modified SST was obtained from ocean general circulation model runs with space- and time-varying phytoplankton abundances from Coastal Zone Color Scanner data. The atmospheric simulations indicate that phytoplankton amplify the seasonal cycle of the lowest atmospheric layer temperature. This amplification has an average magnitude of 0.3°K but 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.

Received 21 January 2003; accepted 14 April 2003; published 2 August 2003.

Index Terms: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 3339 Meteorology and Atmospheric Dynamics: Ocean/atmosphere interactions (0312, 4504); 4855 Oceanography: Biological and Chemical: Plankton; 4847 Oceanography: Biological and Chemical: Optics.

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