Hair-ice, fungal guttation droplets, ice ribbons and needle ice from a chemical perspective

As a result of global warming, now evident also in temperate latitudes, longer periods of snow-free winters, instead with plenty of precipitation are becoming increasingly common. If the temperatures then fall below freezing point, one can, with a little luck, discover hair ice - hair-like, flexible structures reaching up to 10 cm in length without any ramifications.

This natural phenomenon, already described in 1918 by Alfred Wegener, was a mystery for a long time. Only in the 21^st century a fungus (Exidiopsis effusa) was discovered as the causative agent [1].

Hair ice develops exclusively on rotten hardwoods on/in which this fungus is present, at high humidity, preferably windless, and temperatures slightly below freezing. Once infected, corresponding branches can be repeatedly elicited hair-rise growth under optimal conditions (field & climate chamber). Hair ice, unlike frost needles, arises from the base. At the onset of hair-ice melt a very thin fibre becomes apparent, which carries brownish water drops. Melting water samples show complex mass spectra similar to dissolved organic carbon e.g. from terrestrial/ marine waters, soil extracts or aerosols.

Hair ice samples of various tree species were desalted, concentrated by solid phase extraction and subsequently analyzed by flow injection analysis in a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer, equipped with an ESI source and a 7 T supra-conducting magnet (LTQ-FT Ultra, ThermoFisher Scientific) - the key technique for the analysis of complex samples, simultaneously providing molecular level details of thousands of compounds. As main result, complex, but almost identical spectra were found. For their chemical characterization van Krevelen diagrams, typical to classify samples regarding polarity and aromaticity were plotted. By comparison with references biopolymer substance classes were derived. As result, lignin and tannin could be detected as the main hair-ice substance classes, supposed to act as freezing catalyst as well as recrystallization inhibitor.

For the question, if and what happens in summer, we sampled in several years guttation droplets, too – of this fungus and for comparison from a fungus of another family. Both samples were carbon riche, but only the samples from Exidiopsis effusa show such a complex DOC-spectrum, but in contrast to hair ice peak depleted with mainly tannin assignment.

Popular scientific publications have led to an increasing interest in hair ice and related phenomena in recent years. We have received spectacular photos of various ice structures, followed by first samples of needle ice and ice ribbons. After initial measurements for their C content, HPLC-MS investigations still with a triple quadrupole mass spectrometer have been performed. For final analyses a cooperation with a FTICRMS working group is now sought.

[1] D. Hofmann, G. Preuss and C. Mätzler (2015) Biogeosciences 12: 4261–4273