WISSARD: Biogeochemical explorations below the Whillans Ice Stream
Dr Jill Mikucki, University of Tennessee, USA
Antarctic subglacial aquatic environments are diverse ecosystems ranging from fresh to hypersaline. There has been significant interest in exploring these sub-ice water worlds since their discovery, for microbiological, glaciological, geochemical and astrobiological science aims. The Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) project focused on the hydrological system beneath the Whillans Ice Stream in West Antarctica. Subglacial Lake Whillans (SLW) ultimately drains into a subglacial estuary at the grounding zone of the Whillans Ice Stream (WGZ). Here we highlight initial results from the geomicrobiology component of WISSARD (aka GBASE), which examined water and sediments, collected from both SLW and WGZ, using a combination of biogeochemical and genomic measurements. The presence of active microbial life in these cold, dark environments has now been confirmed. The most abundant phylotypes detected in the water and sediments of SLW were related to chemolithotrophic organisms that utilize reduced N, S and Fe supporting the notion that subglacial environments are chemosynthetic, deriving their energy from bedrock minerals.
Microbiology: Lake Ellsworth
Professor David Pearce, Northumbria University, British Antarctic Survey (BAS) and University Centre in Svalbard (UNIS)
Following an unsuccessful attempt to access Lake Ellsworth last season, a number of lessons were learned in the field about the microbiology of deep Antarctic subglacial lake access, and in particular, the limitations in our knowledge of some of the most basic relevant microbiological principles. In this paper, I will focus on five of the core challenges faced, and describe how these were addressed and what we have learnt from the first attempt at accessing Lake Ellsworth. The five areas covered are: the environment of the field camp and the activities that took place there; the engineering processes surrounding the hot water drilling; sample handling, including recovery, stability and preservation; clean access and removal of sample material and the biodiversity and distribution of bacteria around the Antarctic. Issues raised will draw upon experience working with other Antarctic lake systems, including the lakes on Signy Island, on the Antarctic Peninsula at Lake Hodgson and new data from the field site at Lake Ellsworth itself. Ongoing research to better define and characterize the behaviour of microbial populations in response to this type of activity will be discussed.
Microbiology: Lake Vostok
Dr Sergey Bulat, Petersburg Nuclear Physics Institute, NRC Kurchatov Institute, Russia
The objective was to search for microbial life in the subglacial Lake Vostok (buried beneath 4-km thick East Antarctic ice sheet) by studying the accretion ice (naturally slowly frozen lake water) as well uppermost water layer entered the borehole upon lake entry (February 5, 2012) and then shortly got frozen within. The latest samples included the drill bit water frozen on a drill bit upon lake enter along with re-drilled borehole-frozen water ice.
The comprehensive analyses (constrained by Ancient DNA research criteria) showed that the accretion ice in general contains the very low microbial biomass. The only ice containing mica-clay inclusions (type I) allowed the recovery of few bacterial phylotypes all passing numerous contaminant controls. They included well-known chemolithoautotrophic thermophile Hydrogenophilus thermoluteolus (β-Proteobacteria), actinobacterium related to Ilumatobacter fluminis (95% similarity) along with unidentified unclassified bacterium AF532061 (92% similarity with closest relatives). In contrast, the deeper accretion ice (type II) with no sediments present gave no reliable signals.
As for the first lake water samples all they proved to be contaminated with drill fluid. The drill bit water was heavily polluted with drill fluid (at ratio 1:1) while borehole-frozen water samples were rather cleaner but still contained numerous micro-droplets of drill fluid. The cell concentrations measured by flow cytofluorometry showed 167 cells per ml in the drill bit water sample and 5.5 - 38 cells per ml in borehole-frozen samples.
DNA analyses came up with total 49 bacterial phylotypes discovered by sequencing of different regions of 16S rRNA genes. Of them only 2 phylotypes successfully passed all contamination criteria. The 1st remaining phylotype w123-10 proved to be hitherto-unknown type of bacterium showing less than 86% similarity with known taxa. Its phylogenetic assignment to bacterial divisions was also unsuccessful except it showed reliable clustering with the above mentioned unidentified bacterium detected in accretion ice. The 2nd phylotype is still dubious in terms of contamination. It showed 93% similarity with Janthinobacterium sp of Oxalobacteraceae (Beta-Proteobacteria) – well-known ‘water-loving’ bacteria. No archaea were detected in lake water frozen samples.
Thus, the unidentified unclassified bacterial phylotype w123-10 along with another one (AF532061) might represent ingenious cell populations in the subglacial Lake Vostok. The proof may come with farther analyses of cleanly collected lake water.
Physical and Chemical controls on life in the deep subsurface
Professor John Parnell, University of Aberdeen, UK
The distribution of life in the continental subsurface is controlled by a range of physical and chemical factors. The fundamental requirements are for space to live, carbon for biomass, and energy for metabolic activity. These are inter-related, such that adequate permeability is required to maintain a supply of nutrients, and facies interfaces are especially important to allow a juxtaposition of porous habitats with nutrient-rich mudrocks. Viable communities extend to several kilometres depth, diminishing downwards with decreasing porosity. Carbon is contributed by recycling of organic matter originally fixed by photosynthesis, and methanogenesis using crustal carbon dioxide. In the shallow crust, the recycled component predominates, as processed kerogen or hydrocarbons, but carbon dioxide may be significant in deeper, metamorphosed crust. Hydrogen to fuel chemosynthesis is available from radiolysis, mechanical deformation and mineral alteration. Activity in the sub-continental deep biosphere can be traced through the geological record back to the Precambrian. Before the colonization of Earth’s surface by land plants, a geologically recent event, subsurface life probably dominated the planet’s biomass.
In regions of thick ice sheets, the base of the ice sheet where liquid water is stable can be regarded as a deep biosphere habitat. This environment may be rich in dissolved organic carbon and nutrients accumulated from dissolving ice, with a potentially significant input of both from aerosols precipitated at the surface, in addition to a distinctive contribution of nutrients and gases from the glacial crushing of bedrock.