Ice nucleating properties of the sea ice diatom Fragilariopsis cylindrus and its exudates

• Main Authors: Eickhoff, Lukas, Bayer-Giraldi, Maddalena, Reicher, Naama, Rudich, Yinon, Koop, Thomas
• Format: Text
• Language: English
• Published: 2022
• Subjects: Antarctic; Southern Ocean; The Antarctic; Antarc*; Sea ice
• Online Access: https://doi.org/10.5194/bg-2022-113; https://bg.copernicus.org/preprints/bg-2022-113/

In this study, we investigated the ice nucleation activity of the Antarctic sea ice diatom Fragilariopsis cylindrus . Diatoms are the main primary producers of organic carbon in the Southern Ocean and the Antarctic sea ice diatom F. cylindrus is one of the predominant species. This psychrophilic diatom is abundant in open waters and within sea ice, and it has developed several mechanisms to cope with the extreme conditions of its environment, for example the production of ice-binding proteins (IBP) and extracellular polymeric substances, known to alter the structure of ice. Here, we investigated the ice nucleation activity of F. cylindrus using a microfluidic device containing individual sub-nanoliter (~90 µm) droplet samples. The experimental method and a newly implemented Poisson statistics-based data evaluation procedure applicable to samples with low ice nucleating particle concentrations were validated by comparative ice nucleation experiments with well-investigated bacterial samples from Pseudomonas syringae (Snomax). The experiments reveal an increase of 7.2 °C in the ice nucleation temperatures for seawater containing F. cylindrus diatoms when compared to pure seawater. Moreover, also F. cylindrus fragments show ice-nucleation activity, while experiments with F. cylindrus ice binding protein ( fc IBP) show no significant ice nucleation activity. A comparison with experimental results from other diatoms suggests a universal behaviour of polar sea ice diatoms and we provide a diatom mass-based parameterization of their ice-nucleation activity for use in models.