Fast Phytoplankton Growth Rates as a Key to Atmospheric Ice Nucleation

The ocean is a vast source of marine aerosol and a potential source of aerosols capable of catalyzing atmospheric ice nucleation events. Not only does the concentration of marine aerosols produced throughout the phases of a phytoplankton bloom, the chemical and microphysical traits of emitted aerosols do as well. Through laboratory and field measurements, we investigated marine aerosol as ice nucleating particles (INP) by growing two very different representative phytoplankton taxa (a diatom and a cyanobacterium) in controlled laboratory experiments. In both cases, aerosol produced from the cultures were effective immersion INP at temperatures significantly warmer than homogeneous freezing (approximately -38 degrees C), particularly during exponential growth of the phytoplankton. During exponential growth, the aerosol were effective immersion INP at warmer temperatures (-26 to -15 degrees C) compared to the stationary and death phases of the culture (-38 and -28 degrees C, respectively). Similarly, in the North Atlantic Ocean, observations of the most effective marine INP are parallel to observations of high phytoplankton net growth rates. Taken together, our laboratory and field results indicate that phytoplankton physiological status is a reliable predictor of effective INP, more so than either biomass or taxonomic affiliation.