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Stimulation of ice nucleation by marine diatoms


Atmospheric aerosol particles serve as nuclei for ice-crystal formation. As such, these particles are critical to the generation of cirrus clouds, which form from gas and liquid water1. Atmospheric aerosols also initiate ice formation in warmer, mixed-phase clouds, where ice crystals coexist with aqueous droplets1. Biogenic aerosol particles of terrestrial origin, including bacteria and pollen, can act as ice nuclei2. Whether biogenic particles of marine origin also act as ice nuclei has remained uncertain3,4,5. We exposed the cosmopolitan planktonic diatom species Thalassiosira pseudonana to water vapour and supercooled aqueous sodium chloride under typical tropospheric conditions conducive to cirrus-cloud formation. Ice nucleation was determined using a controlled vapour cooling-stage microscope system. Under all conditions, diatoms initiated ice formation. The presence of diatoms in water increased the temperature for ice formation up to 13 K, and in aqueous sodium chloride, ice formed at temperatures up to 30 K higher than when diatoms were not present. In addition, diatoms initiated ice formation from water vapour at relative humidities as low as 65%. The rate of ice nucleation was rapid and independent of surface area. We suggest that marine biogenic particles such as diatoms help explain high values and seasonal variations6,7 in ice-nuclei concentrations8,9,10 in subpolar regions.

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Figure 1: Freezing and melting of aqueous NaCl droplets containing intact and fragmented diatoms.
Figure 2: Temperature and RHice ranges of deposition and immersion ice nucleation and water uptake of intact and fragmented diatoms.


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We thank S. Palma and N. Fisher for providing diatom cultures and J. Radway for assistance in diatom preparation. This work was supported by the NOAA Climate Program Office, Atmospheric Composition and Climate Program.

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D.A.K. initiated and supervised project, designed and developed ice nucleation experiments, and led manuscript preparation. P.A.A. developed diatom particle preparation, conducted ice-nucleation experiments, and contributed to writing the manuscript. B.W. conducted ice-nucleation experiments, and contributed to writing the manuscript. J.Y.A. supervised preparation of phytoplankton cultures and contributed to the manuscript writing.

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Correspondence to D. A. Knopf.

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Knopf, D., Alpert, P., Wang, B. et al. Stimulation of ice nucleation by marine diatoms. Nature Geosci 4, 88–90 (2011).

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