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A microbial approach to subglacial biogeochemistry Methane export, microbial assemblages, and geochemical energy sources of a Greenland subglacial catchment

Bristol student theses: Doctoral ThesisDoctor of Philosophy (PhD)

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Abstract

The past two decades demonstrated how subglacial environments are not devoid of life, that the bed of glaciers and ice sheets harbour active microbial communities and in turn, that these ecosystems may impact on biogeochemical cycles outside of the cryosphere. Despite their putative importance, most of our understanding of subglacial microbial communities derive from conceptual models, and there remains large uncertainties as to how widespread and
(biogeochemically) influential these microorganisms are beneath the ice, as well as to how (or if) such communities can remain biogeochemically “relevant” over glacial timescales. The present thesis aimed at assessing the metabolic strategies employed by, as well as the impact of, microbial communities indigenous to subglacial ecosystems, and to study the hydrological, geochemical, and mechanical processes that shape and sustain such communities beneath the ice. More specifically, research here focused on a large, well-studied, catchment of the Greenland Ice Sheet (GrIS) to evaluate the methanogenic footprint of the catchment, the make-up of the microbial
communities exported from bulk meltwater runoff, as well as the influence of bedrock comminution in fuelling subglacial microbial communities. High-resolution in situ sensor measurements of bulk runoff hydrochemistry, as well as stable-isotope and molecular analyses, revealed the GrIS catchment to be a net source of microbial methane to the atmosphere. Molecular (16S rRNA) analyses also hinted that chemolithotrophy centred on both iron and methane cycling likely plays a key role in sustaining local subglacial microbial populations
beneath the ice, as well as how glacial hydrology can shape microbial communities beneath the catchment. Lastly, laboratory incubations indicated that crushing of bedrock material liberate bioavailable energy (e.g. H2), nutrients (NO3 - and PO4 3- ) and also organic carbon (acetate and formate) to indigenous subglacial populations indicating that bedrock comminution by moving ice masses likely act as a microbial fuel to subglacial ecosystems. All in all, results here further the importance of subglacial biota in the context of global biogeochemical cycles, as well as support previous conceptual models on the microbial distribution and energy sources beneath today’s ice masses.

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Original languageEnglish
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Award date7 May 2019

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