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Characterization of Marine Biogenic Atmospheric Ice Nucleating Particles
Abstract
Aerosol may act as ice nucleating particles (INPs) that catalyze the formation of ice containing clouds at temperatures above the homogeneous nucleation threshold (-38 °C). Aerosol enriched in organic matter may be derived from phytoplankton primary production in marine environments or soil and plant fragments in terrestrial environments. Biogenic aerosol plays an impactful, but poorly constrained, role in ecosystems, biogeochemical processes, and the Earth’s climate system. This dissertation focuses on understanding the ice nucleation efficiency of globally abundant biomolecules and marine phytoplankton. A marine coccolithophore (Emiliania huxleyi) and coccolithovirus (EhV-207) were used as a model system during exponential growth and viral lysis in a marine aerosol reference tank (MART). Viral interactions with E. huxleyi did not enhance the production of efficient INPs. The mean freezing temperatures of sea spray aerosol (SSA) during viral production and lysis were statistically lower (range of -26.9 to -29.6 °C) compared to pre-viral infection and phytoplankton growth (range of -25.9 to -28.3 °C). The results during active growth of E. huxleyi contrast with previous results of SSA from other phytoplankton species (Thalassiosira weissflogii and Synechococcus elongatus), which had the highest ice nucleation efficiency during fast growth rates. Therefore, differences in chemical composition and physical characteristics may play a role in determining the ice nucleation efficiency of organic matter. To better understand the chemical composition of biogenic INPs, molecules including amino acids, nucleic acids, a peptide, and proteins present in a range of environments were investigated, with immersion mode freezing temperatures ranging from -19 to -26 °C. The globally abundant protein, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), was an extremely efficient INP (-7.9 °C) at high concentration (> 10^-1 mg ml^-1) and present in ambient continental aerosol with up to 2 x 10^-6 ice nucleation active sites per L of air. The ice nucleation efficiency of RuBisCO is potentially controlled by changes in concentration and subsequent aggregation, with a broad range in nucleation temperatures (onset of -6.8 °C and complete freezing at -31.6 °C). However, I demonstrated that proteins are not a universal source of efficient biogenic INPs. Four additional chemically and structurally diverse proteins were weakly effective INPs, irrespective of molecular weight or degree of aggregation. Although a wide range of biogenic material contribute to ice nucleation, only select proteins have shown to have high catalytic efficiency for ice formation over global distributions. Therefore, the chemical composition and molecular-level mechanisms contributing to highly efficient biogenic INPs is important to understand for predictive climate modeling in the future.
Citation
Alsante, Alyssa Nicole (2023). Characterization of Marine Biogenic Atmospheric Ice Nucleating Particles. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /199731.