Nenes, Phytoplankton and cloudiness in the southern ocean

• Main Authors: Nicholas Meskhidze, Athanasios Nenes
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Southern Ocean
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.652.191; http://nenes.eas.gatech.edu/Preprints/PhytoCloud_SCIPP.pdf

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. Marine aerosols strongly affect properties and lifetime of stratiform clouds, influencing the Earth’s radiation budget and climate. The role of oceanic biota in modifying chemical-composition and size-distribution of marine CCN has been one of