Microstructure and phase transitions of sea ice

Sea ice plays a key role in polar climate and ecology as well as applied sciences like ice mechanics and remote sensing. It contains, in dependence on age and growth conditions, typically 10 to 50 % of the salts dissolved in the seawater from which it fre ezes. This salt is situated as liquid brine and solid salt in pore networks and disconnected inclusions. The detailed morphology of these pore networks is, due to resolution limits and the lack of three-dimensional observations, presently not well known. Here we shall utilize synchrotron radiation for non-destructive three-dimensional imaging of sea ice pore networks, to investigate, for the first time, crystallisation phenomena in sea ice with high spatial and temporal resolution. Much of the lack in d etailed knowledge on sea ice is owing to difficulties in bringing sea ice samples from the field to the laboratory, while preventing major changes in its microstructure. Structure-preserving sampling, transport protocols that were tested by us during rece nt years are an important prequisite of the present approach. In particular we will - apply time-resolved X-ray tomographic videomicroscopy to obtain the 3-d temporal evolution of sea ice pore network freezing and melting - apply microfocus X-ray fluor escence and spectroscopy (SXRF) and diffraction (SXRD) to analyse the redistribution of sea salts by eutectic precipitation, diffusive and convective transports - evaluate the role of convective processes in shaping the microstructure by proper in-situ ex periments - determine the vertical variability of parameters relevant to understand sea ice as a habitat of life, its radiative and physical properties: e.g., maximum and minimum pore sizes and anisotropy, specific surface area, global/local permeability, percolation and connectivity thresholds - derive an ab-initio microstructure model to predict sea ice bulk salinity evolution - evaluate the predictability of sea ice microstructure by mesoscopic model