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Published Online November 2, 2006
Science DOI: 10.1126/science.1131779

Research Articles

Submitted on June 26, 2006
Accepted on October 25, 2006

Phytoplankton and Cloudiness in the Southern Ocean

Nicholas Meskhidze 1* and Athanasios Nenes 2

1 School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA.
2 School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA; School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.

* To whom correspondence should be addressed.
Nicholas Meskhidze , E-mail: nmeskhidze{at}ncsu.edu

The effect of ocean biological productivity on marine clouds is explored over a large phytoplankton bloom in the Southern Ocean (SO) using remotely sensed data. Cloud droplet number concentration over the bloom was twice what it was away from the bloom, and cloud effective radius was reduced by 30%. The resulting change in the short-wave radiative flux at the top-of-the-atmosphere was -15W m-2, comparable to the aerosol indirect effect over highly polluted regions. This observed impact of phytoplankton on clouds is attributed to changes in the size-distribution and chemical-composition of cloud condensation nuclei (CCN). We propose that secondary organic aerosol (SOA), formed from the oxidation of phytoplankton-produced isoprene, can affect chemical composition of marine CCN and impact cloud droplet number. Model simulations support this hypothesis, indicating that 100% of the observed changes in cloud properties can be attributed to the isoprene SOA.


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Science. ISSN 0036-8075 (print), 1095-9203 (online)