Subglacial Antarctic lake exploration: first results and future plans

WISSARD: Biogeochemical explorations below the Whillans Ice Stream

Dr Jill Mikucki, University of Tennessee, USA

Abstract

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)

Abstract

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

Abstract

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.

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Physical and Chemical controls on life in the deep subsurface

Professor John Parnell, University of Aberdeen, UK

Abstract

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.

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A decade of progress in observing and modelling Antarctic subglacial water systems

Dr Helen Fricker, The Scripps Institution of Oceanography, USA

Abstract

In the decade since we discovered that satellite altimetry could be used to detect activity of Antarctic subglacial water systems, much progress has been made in our understanding of these dynamic systems. Focusing primarily on the Whillans/Mercer ice streams, West Antarctica, and Recovery Glacier, East Antarctica, we present some of the key results of monitoring with a variety of height data: ICESat laser altimetry; CryoSat-2 radar altimetry; IceBridge airborne laser altimetry; and ground-based continuous GPS experiments (deployed in hydrologically-active regions, as determined by altimetry). For some lake systems we have been able to construct a full decade of lake activity, which reveals internal variability on timescales ranging from days to years, indicating that long time-series are critical to understanding these systems. We also show results of regional-scale modeling where satellite-derived water volume estimates are reproduced by draining lakes through channels carved into the subglacial sediment instead of the overlying ice. Last, we show results from the Whillans Ice Stream demonstrating that a subglacial lake flood event significantly changes regional ice dynamics. This transformational decade in Antarctic subglacial water research has moved us significantly closer to understanding the process sufficiently to include it in ice-sheet models.

Presented by Mr Matthew Siegfried.

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Frontiers in Antarctic subglacial hydrology

Dr Neil Ross, Newcastle University, UK

Abstract

Our understanding of Antarctic subglacial hydrological systems has been transformed over the past 20 years.  Despite this, however, these systems are currently conceptualised and modelled in a very simple way (e.g. assuming an impermeable, homogenous subglacial bed). Definition of the geometry, form and flow of the ice sheet, and the morphology of the subglacial bed, has also been limited, both temporally and spatially.

We report recent developments in the investigation and characterisation of ice sheet subglacial hydrology, focusing on: (a) long-distance connectivity of subglacial hydrological networks (i.e. from ice divides to grounding lines and beyond); (b) interaction between the ice sheet and underlying hydrogeological systems; and (c) targeted surveys of satellite-identified active subglacial lakes by radio-echo sounding surveys. We discuss these developments in terms of their implications for the modelling of the Antarctic subglacial hydrological system, the dynamics of the overlying ice sheet and for the direct sampling of aquatic subglacial environments.

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Advances in modelling subglacial lakes and their interaction with ice sheets

Dr Frank Pattyn, Universite Libre de Bruxelles, Belgium

Abstract

Subglacial lakes have long been considered hydraulically isolated water bodies underneath ice sheets. Prior to 2005 they seemed located in bedrock depressions, acting as a constant reservoir of subglacial water and primarily situated in the East Antarctic interior. This view changed radically with the advent of repeat-pass satellite altimetry and the discovery of multiple lake discharges and water infill, associated with water transfer over distances of more than 200 km. The more widespread distribution of subglacial lakes also exhibited an influence on ice dynamics, leading to glacier acceleration. Recent modelling has also demonstrated that subglacial melting under the Antarctic ice sheet is more widespread than previously thought, and subglacial melt rates may explain the availability for water storage and transport.

Modelling of subglacial water discharge in subglacial lakes essentially follows Jökulhlaup hydraulics based on R-channels. Recent evidence points also to the development of channels in deformable sediment (West Antarctica), where the exchange of water between till and the interface is significant. Most active subglacial lakes are therefore short-lived and respond rapidly to upstream variations. Only recently have active subglacial lakes been witnessed underneath the Greenland ice sheet, where water input is essentially from surface melt and percolation through englacial conduits.

Large Antarctic subglacial lakes (Subglacial Lakes Vostok, Concordia and Ellsworth) exhibit complex interactions with the ice sheet due to water circulation, similar to oceans. Such lakes have also been found adequate test cases for improving our knowledge on coupling ocean and ice sheet/ice shelf models.

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Airborne glacier geophysics

Dr Duncan Young, University of Texas at Austin, USA

Abstract

Over the last 25 years, a combination of advances in spaceborne and airborne geophysical systems has transformed our view of the major ice sheets in Antarctica and Greenland.  Together, airborne altimetry and radar sounding have highlighted the importance of subglacial hydrology under ice sheets: first as subglacial lakes, then as active hydraulic relays, and finally, as once hypothesized and now directly observed, as organized hydrologic systems underlying much of the ice sheet.  Ice penetrating radar technology (including sensitivity to the relative strength of incoherent scattering and coherent reflection), survey design, and coverage density now allow the identification of water bodies independently from ice losses, characterization of water system geometry, and more accurate routing of water through the network.

We explore two cases in this contribution: the interior water systems of the Siple Coast of the West Antarctica Ice Sheet, that largely lack the surface expression of actively recharging water systems but feed very active water systems downstream; and the great basins of East Antarctica, which host networks of active subglacial water systems in an environment of varying basal roughness.  These systems were both surveyed in recent years by a coherent 60 MHz ice penetrating radar with extensive heritage.

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Technologies for retrieving sediment cores in Antarctic subglacial settings

Professor Dominic A Hodgson, British Antarctic Survey, UK

Abstract

Accumulations of sediments from deep 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 characterise life in subglacial settings. Retrieving subglacial sediment cores presents several unique challenges to existing sediment coring technologies.  This paper briefly reviews the history of sediment coring 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 and Larsen Ice Shelf), under ice streams (e.g. Rutford 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.

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Glacial geology and geophysics: Lake Whillans

Dr Slawek Tulaczyk, University of California Santa Cruz, USA

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Sedimentary climate records: ANDRILL and beyond

Dr Rob McKay, Victoria University of Wellington, New Zealand

Abstract

Over the past 5 decades around two dozen drill holes from the Antarctic margin, and studies from scattered outcrops on land, have provided a simple history of ice sheet development and behaviour since the first continental ice sheet formed 34 million years ago. Here we review Antarctic cooling history since peak temperatures of the Middle Eocene Climatic Optimum (~ 50 million years ago) to provide context for what might be learned about biota, climate and ice cover in the continental interior from sediment cores taken beneath subglacial lakes and sedimentary basins. However, the cored 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 the Antarctic records with more continuous “far-field” proxy records of ice volume and deep sea temperature. To achieve this, a broad integrated portfolio of drilling and coring missions is still required that encompasses the existing methodologies of ship- and sea ice-/ice shelf-based drilling platforms through to recently developed seafloor-based drilling and subglacial access systems. An ambitious goal for our community is the development of coring systems that can recover deep sediment cores from beneath the grounded regions of the West and East Antarctic Ice Sheet. We will discuss of the outstanding Antarctic paleoclimate problems that could be addressed by such methods.

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Geology and Environments of Subglacial Lake Vostok

Dr German Leychenkov, Research Institute for Geology and Mineral Resources of the World Ocean, Russia

Abstract

Reconstruction of geological (tectonic) structure and environments of subglacial Lake Vostok is based on geophysical surveys and study of mineral inclusions found in cores of accreted ice. Seismic investigations conducted in the southern part of Lake Vostok show very thin (200–300 m) sedimentary cover overlying crystalline basement. Last 12-14 m.y. the rate of sedimentation in Lake Vostok was extremely low and so most of sediments are inferred to be deposited during temperate-glacial condition in Oligocene to middle Miocene time (c. 34-14 m.y.). Composition of bottom sediments can be proposed from mineral inclusions found in cores of accreted ice. Inclusions are represented by soft aggregates consisting mainly of clay-mica minerals and micron-sized quartz grains. Some of these inclusions contain subangular to semi-rounded rock clasts (siltstones and sandstones) ranging from 0.3 to 8 mm in size. Rock clasts are thought to be products of ice erosion of a Neoproterozoic sedimentary basin located to the west of Lake Vostok. Ditrital zircon grains identified in rocks clasts show the ancient (0.8−1.2 Ga and 1.6−1.8 Ga) age of provenance which is the Gamburtsev Mts area. Crystals of sulfides also found in soft aggregates support an assumption about modern hydrothermal activity in Lake Vostok. After unsealing of Lake Vostok, its water (frozen and sampled next season) was also studied. SEM and microprobe analyses discovered micrograins of quarts, mica and calcium carbonate (10-50 mkm across) which are proposed to come from the lake. This fact denotes existence of fine-grained suspension and water circulation in the southern part of Lake Vostok.

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Unlocking Lake Vostok: Lessons and implications for future full-scale investigations of the lake

Dr Vladimir Lipenkov, Arctic and Antarctic Research Institute (AARI), Russia

Abstract

The deep holes drilled at Vostok Station by the Russian Antarctic Expedition reached the surface of subglacial Lake Vostok twice – on February 5 2012 and January 25 2015. The first unsealing of the lake was characterized by uncontrolled movements of fluids in the hole, resulting eventually in the unexpectedly high water rise in the hole to 382 m above the lake surface. The experience we gained from the first lake unsealing was taken into account during the second one which allowed us to improve the performance of the operation. The strict fluid pressure and level controls ensured a moderate water rise in the hole close to the desired height (about 50 m). However, the rapid (almost instantaneous?) formation of a bright white solid substance in the drilling fluid-water interaction zone was observed in both cases and prevented any attempt to sample liquid lake water. This substance was preliminary identified as a mixture of ice and clathrate-hydrate of the hydrochloroflurocarbon (HCFC-141b), the densifier of the drilling fluid. After the second lake unsealing this solid matter filled up more than 10 meters of the borehole length separating the drilling fluid from the frozen lake water. Based on the results of the two attempts to unseal the lake we propose a refined approach to the problem of using the existing deep hole as an access hole for investigation of Lake Vostok. The new data obtained from the borehole surveys and accreted ice core studies extended to the ice-water interface are discussed.

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Clean subglacial access: prospects for future deep hot-water drilling

Dr Keith Makinson, British Antarctic Survey, UK

Abstract

Accessing and sampling subglacial environments deep beneath the Antarctic Ice Sheet presents several unique challenges to existing drilling technologies. With over half of the ice sheet believed to be underlain by liquid water and much of it forming a subglacial drainage network, any drilling activities must conform to international agreements on stewardship and environmental protection, making clean hot water drilling the most viable option. Such a drill and its water recovery system must operate at significantly greater depths than previous hot water drills, remaining fully operational after accessing the local hydrological system whilst avoiding the destabilisation of potentially large volumes of accumulated gas hydrates. The Lake Ellsworth project developed a comprehensive plan for deep (>3000 m) subglacial lake research but during fieldwork in December 2012, drilling was halted after a succession of equipment failures culminated in a failure to link with a subsurface cavity and abandonment of the access holes. The lessons learned from this experience are substantial. Also drawing on experience from WISSARD, IceCube, and other recent hot water drilling activities, some of the development and testing of alternative drilling equipment, tools and techniques essential for future deep drilling is now being undertaken. The most viable technical options and operational scenarios based on current understanding will be presented for future deep and clean subglacial access programmes.

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Enabling clean access into subglacial Lake Whillans: development and use of the WISSARD hot water drill system

Dr Frank Rack, University of Nebraska-Lincoln, USA

Abstract

In June 2011 the three lead institutions of the WISSARD (Whillans Ice Stream Subglacial Access Research Drilling) Project contracted the University of Nebraska’s Science Management Office (UNL SMO) to design, build and operate a hot water drill system that could be used to provide clean access into subglacial environments, such as Subglacial Lake Whillans (SLW) and the grounding zone (GZ) of the Ross Ice Shelf. The timeline, scope and budget of the project presented many challenges that were each addressed in turn to enable the successful clean entry into SLW in January 2012. We will describe the primary requirements, constraints, and technical approaches that were evaluated and/or implemented in order to accomplish the goal of achieving successful clean entry into SLW to support the scientific sampling, data acquisition, and other activities that followed. We will also present the primary lessons learned from developing and operating the hot water drilling system and clean technologies for the WISSARD project and will describe how these insights may contribute to future planning efforts aimed at continuing the scientific exploration and instrumentation of subglacial lakes and other subglacial environments in Antarctica.

Presented by Professor John Priscu.

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Summary of discussions and closing remarks

Mahlon Kennicutt, Texas A&M University, USA

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