Chemical constituents trapped within glacial ice provide a unique record of climate, as well as repositories for biological material such as pollen grains, fungal spores, viruses, bacteria and dissolved organic carbon. Past research suggests that the veins of polycrystalline ice may provide a liquid microenvironment for active microbial metabolism fueled by concentrated impurities in the veins. Despite these claims, no direct measurements of impurity concentration in ice veins have been made. Using micro-Raman spectroscopy, we show that sulfate and nitrate concentrations in the veins of glacial ice from Greenland (Greenland Ice Sheet Project 2) and Antarctic (Newall Glacier and a Dominion Range glacier) core samples were 10 4 and 10 5 times greater than the concentrations measured in melted (bulk) core water. Methanesulfonate was not found in the veins, consistent with its presence as particulate matter within the ice. The measured vein concentration of molecular anions implies a highly acidic (pH < 3) vein environment with high ionic strength (mM-M). We estimate that the vein volume provides 16.7 and 576 km 3 of habitable space within the Greenland and Antarctic ice sheets, respectively, which could support the metabolism of organisms that are capable of growing in cold, high ionic strength solutions with low pH.

Icy 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.

Biogenic sulfur compounds such as dimethyl sulfide (DMS) are important contributors to the global carbon cycle. The differential Raman cross section of DMS relative to the nitrogen fundamental, σ DMS , has been measured at several excitation wavelengths in order to assess the applicability of Raman spectroscopy for the direct quantitative measurement of this compound. At 488 nm, σ DMS for the ν 6 carbon-sulfur stretching mode was found to be 4.9 ± 1.6, while for the ν 2 carbon-hydrogen stretching mode it was 2.8 ± 0.9. Using, KrF laser excitation, values for σ DMS could be measured simultaneously at two excitation wavelengths, 248.32 and 248.69 nm. The average values of σ DMS for 248-nm excitation based on measurements at these two excitation wavelengths were 3.5 ± 1.4 for the carbon-sulfur stretching mode and 4.6 ± 0.6 for the carbon-hydrogen stretching mode. The results indicate that no significant resonance enhancement of σ DMS for either mode occurs, although they show some slight enhancement of the cross section for the ν 2 band (C-H stretching mode). It was concluded that the measured values of σ DMS are high enough to allow the quantitative detection of DMS at the millimolar level.

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