The effect of nanoparticles on the evolution of microstructure in polar ice (NEMI)
Dr. Maddalena Bayer-Giraldi
Helmholtz-Zentrum für Polar- und Meeresforschung
The soft ice observed in Antarctic and Greenland firn and glacial ice layers is related to small grain size and the presence of impurities. It is generally assumed that the impurities control the grain size by pinning grain boundaries and thus inhibiting their migration. However, large uncertainties persist on which impurities are responsible for this effect. Data on insoluble microparticles and soluble ions give an incomplete picture of their presence in ice and of their relevance in inhibiting grain boundary migration. Recent data show a clear evidence that calcium ion concentration affects densification in firn and shallow ice. There is no reason to assume that this correlation should not hold for deeper ice. However, it is unknown whether the effect is caused directly by calcium or if it is a proxy for some other impurity. Theory stresses the role of nanoparticles, but calculations are not supported by experimental evidence due to the fact that this particle size range is difficult to detect in ice. Therefore, in order to understand how nanoparticles affect grain boundary migration, we apply different kinds to polycrystalline ice. We focus on antifreeze proteins (AFPs) from polar diatoms, particles known to inhibit grain growth. We regard these proteins as analogues of nanoparticles within ice. However, considering that Arctic and Antarctic deep ice is populated by microorganisms, which may have reached the central regions by wind transport and then been included in the ice sheets, and considering that AFPs are widespread in the polar regions, it is conceivable that proteins are indeed present in Antarctic and Greenland ice. Besides AFPs, calcium and selected other nanoparticles will be applied to the experiments. We will work mainly with frozen polycrystalline particle solution, fine-grained and free of deformations through a phase-transition method from ice I to ice II and back to ice I. Grain boundaries will be observed in relation to time, temperature, particle type and concentration. Grain microstructure will be determined by optical microscopy, Raman spectroscopy and an Automated Fabric Analyzer. In a second step we will analyze snow doped with particles, thus resembling natural conditions. Furthermore, in order to understand how particles behave during boundary migration, whether they are overgrown or dragged along by the migrating boundaries, we will determine their localization in ice. In this last step fluorescent nanoparticles will be applied and observed at laser confocal microscopy, choosing the more promising experimental conditions based on the obtained results from previous steps.Addressing the role of nanoparticles in affecting the microstructure of polycrystalline ice with special emphasis on AFPs, this project aims to close, in an interdisciplinary effort, open gaps in both ice-core analysis and antifreeze research.
Internationaler Bezug: Japan
Förderung von 2013 - 2017