UBC Theses and Dissertations
Properties and sources of ice nucleating substances and ice recrystallization inhibition substances from high latitudes Xi, Yu
Ice nucleating substances (INSs) are substances capable of initiating ice formation. Atmospheric INSs can affect the formations and properties of mixed-phase clouds and ice clouds and thus influence the Earth’s climate system. Despite the importance of INSs, our understanding of the sources, concentrations, and properties of INSs is still limited. This dissertation focuses on INSs from high latitude regions. Sea-ice diatom exudates collected from two locations in the Antarctic caused freezing at temperatures from -17 to -22 °C. The results suggested that sea-ice diatom exudates can act as INSs once emitted to the atmosphere. According to a heat assay and a filter assay, possible candidates for the INSs in the exudate samples from the Ross Sea and the McMurdo Sound are polysaccharide-containing nanogels and protein-containing nanogels, respectively. Cyanobacteria mat exudates from the Antarctic caused freezing at temperatures from -5 to -13 °C, with possible INS candidates being aggregates containing heat-sensitive proteins. These results indicate that cyanobacteria mat exudates can also cause ice nucleation in the atmosphere. Airborne dust samples collected near the Kaskawulsh Glacier contained INSs, which nucleated ice at temperatures from -6 to -23 °C. The ice nucleating ability of the INSs was similar to that of K-feldspar and Icelandic dust at freezing temperatures less than -15 °C. According to a heat assay and an ammonium sulfate assay, the INSs that caused freezing at temperatures warmer than -15 °C were possibly biological materials. The INS concentrations at the site in May 2018 are significantly higher than those predicted with dust concentrations simulated by a global chemical transport model (GEOS-Chem) without the inclusion of highlatitude dust sources. The under-prediction of the GEOS-Chem model suggests that high latitude dust sources should be included in modeling studies of INS. Furthermore, ice recrystallization inhibition substances (IRISs) in cyanobacteria mat exudates were studied to investigate the cold tolerance mechanism of cyanobacteria and the relationship between INSs and IRISs. IRISs were observed in the cyanobacteria mat exudates and the properties of IRISs were different from the INSs in the cyanobacteria mat exudates, with possible IRISs being polysaccharides or heat-stable proteins.
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