Geomicrobiology of the basal ice layer at Svínafellsjökull glacier, SE Iceland

Toubes-Rodrigo, Mario (2017) Geomicrobiology of the basal ice layer at Svínafellsjökull glacier, SE Iceland. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Glaciers occupy 11% of Earth’s total surface and represent a significant but, as yet, poorly characterised ecosystem. As late as the mid-90s glaciers had been regarded as microbiologically sterile environments but there has since been major progress characterising diversity and functioning of glacier microbiota. The supraglacial environment has to-date been prioritised, but crucially the subglacial microbiota remains generally unknown despite their central importance in geochemical cycling. The dark and oligotrophic conditions typical to subglacial environments in general, and sediment entrained basal ice, in particular, are likely to select for chemolithotrophic carbon fixers that, by definition, will enable diverse heterotrophic microbial community development. Therefore, the basal ice microbiota, are likely to play fundamental roles in mineral weathering and geochemical cycling not only within basal ice but also subsequent foreland soil formation upon release. The main aim of this thesis is the first integrated geo-microbiological characterization, of geomorphologically distinct basal ice facies targeting an Icelandic temperate glacier, Svínafellsjökull. Here we show, via novel culture-dependent and -independent next generation molecular rRNA gene marker (16S and ITS) phylogenetics, that basal ice facies harbour a rich and diverse community of bacteria (Proteobacteria and Acidobacteria) and fungi (Ascomycota and Basidiomycota). An abundance of chemolithotrophic species (Thiobacillus, Gallionella, Nitrosospira) characterise the basal ice microbiome that is directly supported in the identified geochemical status of basal ice. The presence of reduced nitrogen species in the ice matrix and iron- and sulphur-rich minerals in basal ice sediment provides added functional support of the predominance of chemolithotrophs in basal ice. Based on total basal ice cell enumeration and export estimates (~1016 cells yr-1) it is clear that chemolithotrophic and heterotrophic microbial communities identified in foreland soils originate from basal ice, as opposed to supraglacial sources. Modelling highlights the importance of microbial activities on the geo-chemistry of the basal ice, e.g. oxidising minerals, acidifying the environment, and increasing the carbon content within the sediment. Once released, basal ice-derived microorganisms can survive the psychrophilic to mesophilic temperatures of the foreland and identified isolates from basal ice and the foreland were affiliated with species that play important roles in weathering and soil formation highlighting the functional importance of the basal ice microbiota both, in glacial and periglacial systems.