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Subglacial ecosystems harbor diverse chemoautotrophic microbial communities in areas with limited organic carbon, and lithological H 2 produced during glacial erosion has been considered an important energy source in these ecosystems. To verify the H 2 -utilizing potential there and to identify the related energy-converting metabolic mechanisms of these communities, we performed metagenomic analysis on subglacial sediment samples from East Antarctica with and without H 2 supplementation. Genes coding for several [NiFe]-hydrogenases were identified in raw sediment and were enriched after H 2 incubation. All genes in the dissimilatory nitrate reduction and denitrification pathways were detected in the subglacial community, and the genes coding for these pathways became enriched after H 2 was supplied. Similarly, genes transcribing key enzymes in the Calvin cycle were detected in raw sediment and were also enriched. Moreover, key genes involved in H 2 oxidization, nitrate reduction, oxidative phosphorylation, and the Calvin cycle were identified within one metagenome-assembled genome belonging to a Polaromonas sp. As suggested by our results, the microbial community in the subglacial environment we investigated consisted of chemoautotrophic populations supported by H 2 oxidation. These results further confirm the importance of H 2 in the cryosphere.

Direct measurement and sampling of pristine environments, such as subglacial lakes, without introducing contaminating microorganisms and biomolecules from the surface, represents a significant engineering and microbiological challenge. In this study, we compare methods for decontamination of titanium grade 5 surfaces, the material extensively used to construct a custom-made probe for reaching, measuring and sampling subglacial Lake Ellsworth in West Antarctica. Coupons of titanium were artificially contaminated with Pseudomonas fluorescens bacteria and then exposed to a number of decontamination procedures. The most effective sterilants were (i) hydrogen peroxide vapour, and (ii) Biocleanse™, a commercially available, detergent-based biocidal solution. After each decontamination procedure the bacteria were incapable of proliferation, and showed no evidence of metabolic activity based on the generation of adenosine triphosphate (ATP). The use of ultraviolet irradiation or ethyl alcohol solution was comparatively ineffective for sterilisation. Hydrogen peroxide vapour and ultraviolet irradiation, which directly damage nucleic acids, were the most effective methods for removing detectable DNA, which was measured using 16S rRNA gene copy number and fluorescence-based total DNA quantification. Our results have not only been used to tailor the Ellsworth probe decontamination process, but also hold value for subsequent engineering projects, where high standards of decontamination are required., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Accumulations of sediment beneath the Antarctic Ice Sheet contain a range of physical and chemical proxies with the potential to document changes in ice sheet history and to identify and characterize life in subglacial settings. Retrieving subglacial sediments and sediment cores presents several unique challenges to existing technologies. This paper briefly reviews the history of sediment sampling in subglacial environments. It then outlines some of the technological challenges and constraints in developing the corers being used in sub-ice shelf settings (e.g. George VI Ice Shelf and Larsen Ice Shelf), under ice streams (e.g. Rutford Ice Stream), at or close to the grounding line (e.g. Whillans Ice Stream) and in subglacial lakes deep under the ice sheet (e.g. Lake Ellsworth). The key features of the corers designed to operate in each of these subglacial settings are described and illustrated together with comments on their deployment procedures., (© 2015 The Author(s).)

It is 4 years since the subglacial lake community published its plans for accessing, sampling, measuring and studying the pristine, and hitherto enigmatic and very different, Antarctic subglacial lakes, Vostok, Whillans and Ellsworth. This paper summarizes the contrasting probe technologies designed for each of these subglacial environments and briefly updates how these designs changed or were used differently when compared to previously published plans. A detailed update on the final engineering design and technical aspects of the probe for Subglacial Lake Ellsworth is presented. This probe is designed for clean access, is negatively buoyant (350 kg), 5.2 m long, 200 mm in diameter, approximately cylindrical and consists of five major units: (i) an upper power and communications unit attached to an optical and electrical conducting tether, (ii)-(iv) three water and particle samplers, and (v) a sensors, imaging and instrumentation pack tipped with a miniature sediment corer. To date, only in Subglacial Lake Whillans have instruments been successfully deployed. Probe technologies for Subglacial Lake Vostok (2014/15) and Lake Ellsworth (2012/13) were not deployed for technical reasons, in the case of Lake Ellsworth because hot-water drilling was unable to access the lake during the field season window. Lessons learned and opportunities for probe technologies in future subglacial access missions are discussed., (© 2015 The Author(s).)

Mounting evidence from models and geological data implies that the Antarctic Ice Sheet may behave in an unstable manner and retreat rapidly in response to a warming climate, which is a key factor motivating efforts to improve estimates of Antarctic ice volume contributions to future sea-level rise. Here, we review Antarctic cooling history since peak temperatures of the Middle Eocene Climatic Optimum (approx. 50 Ma) to provide a framework for future initiatives to recover sediment cores from subglacial lakes and sedimentary basins in Antarctica's continental interior. While the existing inventory of cores has yielded important insights into the biotic and climatic evolution of Antarctica, strata have numerous and often lengthy time breaks, providing a framework of 'snapshots' through time. Further cores, and more work on existing cores, are needed to reconcile Antarctic records with the more continuous 'far-field' records documenting the evolution of global ice volume and deep-sea temperature. To achieve this, we argue for an integrated portfolio of drilling and coring missions that encompasses existing methodologies using ship- and sea-ice-/ice-shelf-based drilling platforms as well as recently developed seafloor-based drilling and subglacial access systems. We conclude by reviewing key technological issues that will need to be overcome., (© 2015 The Author(s).)

Several broadly circular structures up to 16 m in diameter, into which higher strata have sagged and locally collapsed, are present in a tephra outcrop on southwest Öræfajökull, southern Iceland. The tephra was sourced in a nearby basaltic tuff cone at Varða. The structures have not previously been described in tuff cones, and they probably formed by the melting out of large buried blocks of ice emplaced during a preceding jökulhlaup that may have been triggered by a subglacial eruption within the Öræfajökull ice cap. They are named ice-melt subsidence structures, and they are analogous to kettle holes that are commonly found in proglacial sandurs and some lahars sourced in ice-clad volcanoes. The internal structure is better exposed in the Varða examples because of an absence of fluvial infilling and reworking, and erosion of the outcrop to reveal the deeper geometry. The ice-melt subsidence structures at Varða are a proxy for buried ice. They are the only known evidence for a subglacial eruption and associated jökulhlaup that created the ice blocks. The recognition of such structures elsewhere will be useful in reconstructing more complete regional volcanic histories as well as for identifying ice-proximal settings during palaeoenvironmental investigations., (© The Author(s) 2016.)