Rock comminution of subglacial lake sediments as a potential source of energy and nutrients to the Subglacial Lake Whillans microbial ecosystem.

Abstract

Throughout the past couple decades, the study of subglacial environments has shown microbial ecosystems exist under ice sheets and glaciers. The recent access to Subglacial Lake Whillans (SLW) provided, for the first time, the opportunity to observe these environments directly. So far, SLW has been shown to have a diverse and active microbial ecosystem despite the limited access to typical energy sources, such as the atmosphere or in-washed organic matter and oxidising agents. Therefore, SLW, like most other sub ice-sheet environments, is limited to energy sources that exist within it. In this thesis, samples from four depths of a shallow SLW sediment core, were used to evaluate the potential energy contributions from mechanochemical reactions. To do this, samples were crushed and wetted under anoxic conditions and gases released during crushing and the subsequent 40-day incubation of the crushed sediments were measured. Results showed considerable amounts of hydrogen and carbon dioxide, as well as methane (albeit at a lower concentration), which could serve as abiotic sources of energy to methanogenic and methanotrophic microbial communities found in SLW. Further experiments and analysis, to investigate the origins of these gases, revealed crushing produced significant amounts of surface free radicals and H2O2, offering the potential for a wide range of REDOX conditions and reactions to develop in subglacial environments, and consequently, the potential for nutrient cycling within these environments. Finally, analysis of trace gases within the vial headspace and of the water chemistry after incubation provided some further insight into previously overlooked effects of sediment comminution. The presence of several hydrocarbons within the headspace, together with the concentrations of acetate, DOC and DOM within the water hint at the potential recycling of ancient organic matter. Analysis of the water chemistry also showed evidence of fluid inclusion release and the effects of comminution on subglacial weathering.

Date of Award	19 Mar 2019
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Martyn Tranter (Supervisor) & Sandra Arndt (Supervisor)