Polysaccharides─Important Constituents of Ice-Nucleating Particles of Marine Origin

Remote marine regions are characterized by a high degree of cloud cover that greatly impacts Earth's radiative budget. It is highly relevant for climate projections to represent the ice formation in these clouds. Therefore, it is crucial to understand the sources of ice-nucleating particles (INPs) that enable primary ice formation. Here, we report polysaccharides produced by four different aquatic eukaryotic microorganisms (<i>Thraustochytrium striatum</i>, <i>Tausonia pullulans</i>, <i>Naganishia diffluens</i>, <i>Penicillium chrysogenum</i>) as responsible ice-nucleating macromolecules (INMs) in these samples originating from the marine biosphere. By deriving a classical nucleation theory-based parametrization of these polysaccharidic INMs and applying it to global model simulations, a comparison to currently available marine atmospheric INP observations demonstrates a 44% contribution of polysaccharides to the total INPs of marine origin within -15 to -20 °C. The results highlight the relevance of biological INMs as part of the INP population in remote marine regions.