Chemical analysis of ice vein μ-environments

Abstract

ABSTRACTIcy environments (glacial ice and sea ice) can be complex ecosystems, supporting a diversity of communities. In particular, the μ-environments in which bacteria and algae are found are poorly understood. One important habitat is the liquid trapped in the ice, either as veins and triple junctions inherent in the ice structure or as liquid inclusions. μ-Raman spectroscopy is an analytical tool with the potential to characterise qualitatively and quantitatively these liquid μ-environments especially with respect to molecular anions such as nitrate, sulphate, bisulphate and MSA. Using a model system for glacial ice, splat-cooled samples were prepared from aqueous solutions of these anions at varying concentrations (50–75 mM total sulphate, 30–200 mM nitrate, and 10–55 mM MSA). Concentrations of these anions in the vein liquid were measured directly and non-destructively at –15 °C using μ-Raman spectroscopy. In agreement with predicted concentrations in glacial ice veins, it was found that typical ionic concentrations in veins are quite high, with mean concentrations ranging from 0.23 M to 3.5 M depending on anion type and initial concentration. For sulphate solutions, it was also possible to measure vein pH's directly. The observed pH in these systems was extremely low, in some cases ~1. The results of these model studies as well as the implications for ice vein concentrations in natural systems of polycrystalline ice are discussed.