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Microbiology of the subglacial Lake Vostok: First results of borehole-frozen lake water analysis and prospects for searching for lake inhabitants

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Sergey Bulat at Petersburg Nuclear Physics Institute
Sergey Bulat
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Abstract

This article examines the question of the possible existence of microbial life inhabiting the subglacial Lake Vostok buried beneath a 4 km thick Antarctic ice sheet. It represents the results of analysis of the only available frozen lake water samples obtained upon the first lake entry and subsequent re-coring the water frozen within the borehole. For comparison, results obtained by earlier molecular microbiological studies of accretion ice are included in this study, with the focus on thermophiles and an unknown bacterial phylotype. A description of two Lake Vostok penetrations is presented for the first time from the point of view of possible clean water sampling. Finally, the results of current studies of Lake Vostok frozen water samples are presented, with the focus on the discovery of another unknown bacterial phylotype w123-10 distantly related to the above-mentioned unknown phylotype AF532061 detected in Vostok accretion ice, both successfully passing all possible controls for contamination. The use of clean-room facilities and the establishment of a contaminant library are considered to be prerequisites for research on microorganisms from Lake Vostok. It seems that not yet recorded microbial life could exist within the Lake Vostok water body. In conclusion, the prospects for searching for lake inhabitants are expressed with the intention to sample the lake water as cleanly as possible in order to make sure that further results will be robust.
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Opinion piece
Cite this article: Bulat SA. 2016 Microbiology
of the subglacial Lake Vostok: rst results of
borehole-frozen lake water analysis and
prospects for searching for lake inhabitants.
Phil.Trans.R.Soc.A374: 20140292.
http://dx.doi.org/10.1098/rsta.2014.0292
Accepted: 2 September 2015
One contribution of 17 to a Theo Murphy
meeting issue ‘Antarctic subglacial lake
exploration: rst results and future plans’.
Subject Areas:
biogeochemistry, glaciology
Keywords:
Antarctica, subglacial Lake Vostok,
borehole -frozen water, extremophiles,
unknown bacteria, contamination
Author for correspondence:
Sergey A. Bulat
e-mail: bulat@omrb.pnpi.spb.ru
Microbiology of the subglacial
LakeVostok:rstresultsof
borehole-frozen lake water
analysis and prospects for
searching for lake inhabitants
Sergey A. Bulat1,2
1Division of Molecular and Radiation Biophysics, B.P. Konstantinov
Petersburg Nuclear Physics Institute, National Research Centre
‘Kurchatov Institute’, 188300 Gatchina, Russia
2Department of Physical Methods and Devices for Quality Control,
Institute of Physics and Technology, Ural Federal University,
620002 Ekaterinburg, Russia
This article examines the question of the possible
existence of microbial life inhabiting the subglacial
Lake Vostok buried beneath a 4 km thick Antarctic
ice sheet. It represents the results of analysis of the
only available frozen lake water samples obtained
upon the first lake entry and subsequent re-coring the
water frozen within the borehole. For comparison,
results obtained by earlier molecular microbiological
studies of accretion ice are included in this study,
with the focus on thermophiles and an unknown
bacterial phylotype. A description of two Lake
Vostok penetrations is presented for the first time
from the point of view of possible clean water
sampling. Finally, the results of current studies of
Lake Vostok frozen water samples are presented,
with the focus on the discovery of another unknown
bacterial phylotype w123-10 distantly related to the
above-mentioned unknown phylotype AF532061
detected in Vostok accretion ice, both successfully
passing all possible controls for contamination. The
use of clean-room facilities and the establishment
of a contaminant library are considered to be
prerequisites for research on microorganisms
from Lake Vostok. It seems that not yet recorded
microbial life could exist within the Lake Vostok
2015 The Author(s) Published by the Royal Society. Allrights reser ved.
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water body. In conclusion, the prospects for searching for lake inhabitants are expressed with
the intention to sample the lake water as cleanly as possible in order to make sure that further
results will be robust.
1. Introduction
The subglacial Lake Vostok is a well-known giant lake in Eastern Antarctica [1, fig. 1]. Many
works have been performed on clarifying its geophysics, geology, chemistry, gas content,
biogeochemistry and biology, and microbiology in particular [2,3]. The main scientific objective
of the lake entry is to search for unusual microbial life that could cope with its extreme
conditions—pressure reaching 400 bar, temperature close to freezing point, no light, no dissolved
organic carbon [4], very dilute major chemical ions, long-term isolation from the above surface
biota (at least 14 Ma) [5] and very probable excess of dissolved oxygen (in the range of
700–1300 mg l−1)[6,7].
It is likely that the lake existed before Antarctic glaciations, which could be suggested based
on interpretation of its geological setting [8,9], and numerous life forms could have flourished
in the lake before glaciation started. Therefore, it is a big challenge to discover the life, if any,
that remained to thrive in the water body of the lake and its sediments. The present-day lake
access technique is based on electromechanical ice drilling with the use of kerosene drilling
fluid [10,11], which is chemically and microbiologically dirty [12]. Taking into account such a
contamination threat and the very small amounts of microbial cells detected in the accretion
(naturally frozen lake water) ice [13], further research requires the development of special clean
lake entry technologies as well as strict decontamination procedures. It is also crucial to discover
a way to prevent contamination of the devices to be lowered into the lake in order to record its
physical and chemical parameters, to measure dissolved oxygen content and, finally, to provide
researchers with clean samples of water/sediments.
The deepest part of the 5G borehole-recovered ice, starting from the depth of 3539m, consists
of accretion ice, i.e. naturally frozen lake water accreted to the glacier floating above the lake.
Drillers cored this ice for a long time and many samples were provided for different studies,
including research of French [14–17] and US scientists [18–22]. This ice consists of two layers—
accretion ice type I with entrapped minerals, mostly mica–clay (along with small rock fragments)
inclusions, originating from the lake shore, and accretion ice type II composed of very clean giant
monocrystalline ice originating from the deep part of the lake [2].
Comprehensive analyses (constrained by ancient DNA research criteria and performed
with the use of clean-room facilities and microbial DNA-free consumables and reagents) have
showed that the microbial biomass of accretion ice is generally very low. Only ice type I
containing mica–clay inclusions allowed the discovery of a few bacterial phylotypes all passing
numerous contaminant control criteria. They include a well-known chemolithoautotrophic
thermophile Hydrogenophilus thermoluteolus (100% sequence similarity) (β-Proteobacteria), an
actinobacterium related to Ilumatobacter fluminis (95% similarity), along with an unidentified
unclassified bacterium AF532061 (92% similarity to closest relatives) [23–25]. By contrast, the
deeper accretion ice type II with no entrapped sediments gave no reliable signals (no polymerase
chain reaction (PCR) signals or only contaminants [25]). It is worth noting that archaeal DNA was
not detected in both types of accretion ice.
2. Lake Vostok entry and sampling of borehole-frozen lake water
The first entry into Lake Vostok was performed at the depth of 3769.3 m on 6 February 2012. The
water rose up into the borehole to 363 m and froze. With regard to the research programme, a
small sample of frozen water that became stuck in a drill bit during this entry, hereafter drillbit
water, was provided for biological studies. During the next season, 2012–2013, drillers re-cored the
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fast frozen lake water and were able to obtain only 32 m of the ice core. Further drilling operations
of re-coring of this frozen lake water were influenced by the old borehole geometry and went out
into the pristine glacial ice. Three ice samples of this 32 m long ice core (from the topmost full-
cylinder ice core containing kerosene in bubbles to the bottommost moon-shaped ‘milky’ ice),
hereafter borehole-frozen water, were provided for microbiological analyses.
The second entry into the lake occurred at the depth of 3769.15 m some 3 years later, on 25
January 2015. The water rose up again into the borehole to the level of about 70 m and was left to
freeze. In 4 days, drillers re-cored the icy ‘cork’ and obtained about 12m of the new fast frozen
lake water core before the water came up again into the borehole and finally froze at the level
of 65–67 m above the ice–water interface. The bottommost 10 cm (of 12 m core) frozen water ice
segment was provided for microbiological studies.
However, despite the fact that the Russians were the first to enter a subglacial Antarctic lake at
such a great depth (3769 m) and were able to perform the lake entry twice, the drilling technology
used (electromechanical drill along with kerosene drilling fluid with the use of foranes (namely
Freon 141B, 1,1-dichloro-1-fluoroethane, as densifier)) proved to be inappropriate to collect
liquid water in general and clean samples in particular. More technological developments are
needed to face such a challenge, including the development of sophisticated systems consisting
of well-sealed transport modules preventing the contamination of in-module-encapsulated
devices/samplers with the drilling fluid [11] as well as the use of thermal drilling just before
the next lake entry, which is now under discussion.
3. First results from borehole-frozen water of Lake Vostok upon rst lake entry
The main objective of this study was to search for resident microbial life in the subglacial Lake
Vostok by studying the uppermost layer of the water that entered the borehole upon the first lake
entry (5 February 2012) and then was frozen, in comparison with thoroughly studied accretion
ice [23,24]. The fast frozen water samples included the drillbit water along with three samples of
re-cored borehole-frozen water. The fast frozen lake water collected upon the second lake entry
in 2015 is still waiting to be analysed.
Both types of fast frozen lake water samples proved to be contaminated with the drilling
fluid. The drillbit water sample was heavily polluted with drilling fluid (at ratio 1 : 1) while
borehole-frozen water samples were rather clean but still contained numerous microdroplets
of drilling fluid, giving the ice a ‘milky’ appearance. The cell concentrations measured by flow
cytofluorometry showed 167 cells per millilitre in the drillbit water sample while borehole-frozen
water samples contained from 5.5 to 38 cells per millilitre. At the same time, drill fluid analyses
showed about 100 cells per millilitre [12].
The ice samples were strictly decontaminated in the cold-room facilities of LGGE UJF-CNRS,
Université J. Fourier, Grenoble, France (with outer core cut out, rinsed with GC-grade pentane
and ozone treated—depending on the ice sample facture), and meltwater was processed in
clean-room facilities using centrifugal filtering through 5–10 kDa membranes (5 kDa (45.9 nm)
allows us to collect 135 kb DNA fragments). Genomic DNA was also extracted in clean-room
facilities using bead-based cell lysis kits, plastic ware and solutes that were made DNA-free
using 100 kDa membrane filtering and ozone treatment. Primary PCR reactions targeted different
regions (v3–v5, v4–v8, v4–v6, v4 and full gene) of 16S rRNA genes and were again processed in
clean-room facilities while amplicons generated were analysed outside of these facilities and even
not in the same building/country to prevent the clean-room facilities from amplicon carry-over
contamination.
A total of 49 bacterial phylotypes were discovered by sequencing of bacterial 16S rRNA genes.
Of them, only two phylotypes have successfully passed all contamination criteria, including
our own contaminant library [23] consisting of 278 phylotypes (as of June 2014) originating
from various contamination sources (e.g. negative PCR, sham DNA extraction, human-associated
bacteria, drilling fluid, even dust microparticles in clean-room facilities). With no such library the
work on tiny cell biomass is meaningless.
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The first remaining phylotype, hereafter w123-10, proved to be a hitherto-unknown type
of bacterium showing less than 86% sequence similarity to known taxa. Its phylogenetic
assignment to bacterial divisions was also unsuccessful except for the fact that it showed
reliable clustering with the above-mentioned unidentified bacterium AF532061 earlier detected
in accretion ice. The second phylotype is still dubious in terms of contamination. It showed 93%
similarity to Janthinobacterium sp. of Oxalobacteraceae (β-Proteobacteria)—well-known ‘water-
loving’ bacteria, though we do not expect to meet a known representative of Oxalobacteraceae
in Lake Vostok because of its hitherto known physical–chemical conditions. Notably, no Archaea
were detected in all tested samples of frozen lake water.
Regarding 47 contaminant phylotypes detected in drillbit and borehole-frozen lake water
samples, they proved to belong to several bacterial divisions Proteobacteria (33 phylotypes),
Actinobacteria (six phylotypes), Firmicutes (seven phylotypes) and Bacteroidetes (one phylotype)
with predominance of γ-Proteobacteria (19 phylotypes), which indicates that the main sources of
contamination were human-associated and soil bacteria. It means that, even working in clean-
room facilities and trying to avoid bacterial contamination of the human/soil source, we still face
a big challenge and personnel should be taught properly to follow the rules of working with
traces of DNA under clean-room conditions. A low amount of Archaea, if any, inhabit human
skin, which is why they were reasonably not detected in our PCR trials. At the same time, it
means that with no access to clean-room facilities, which includes the use of ultra-clean water,
there is no chance to cope with the bacterial contamination while working with valuable dilute
DNA samples.
4. Expectations and prospects for searching for lake inhabitants
At present, the most important finding is the unidentified unclassified bacterial phylotype w123-
10, which along with another one (AF532061 [23]) may represent indigenous cell populations
in the subglacial Lake Vostok provided they are able to cope with the high dissolved oxygen
content/highly oxidized environment (at least 320 mgl−1) (V. Lipenkov, personal communication,
2015, at this Theo Murphy meeting), which can represent the main constraint for microbial life in
the lake water. At the same time, a kind of proof may come with analyses of a new sample of fast
frozen lake water obtained upon second lake entry (25 January 2015).
However, it is worth noting that there is little hope of finding active (propagating) microbial
populations at the uppermost lake water level, which contacts directly the overcooled water–
glacier interface where the ice accretes. A true challenge would be to collect the water within the
whole water column (680 m below the borehole) and especially closer to sediments where the
water is expected to be warmer and enriched with mineral nutrients. For this, we need to sample
the lake water as cleanly as possible upon further clean lake entry using special water sampling
devices well protected from contamination with drilling fluid. Such devices are planned to be
developed and manufactured at PNPI NRC KI (Russia) based on the experience of UK ‘Ellsworth’
project engineers.
Competing interests. The author declares that he has no competing interests.
Funding. The reported study was partially supported by RFBR, research project RFBR-CNRS_a no. 14-05-93110.
Acknowledgements. French colleagues (J. R. Petit et al., LGGE UJF-CNRS, Grenoble; D. Marie, Biological Station
CNRS, Roscoff) are highly appreciated for providing cold and clean laboratory facilities along with valuable
advice and for measuring cell concentrations. All members of the French GeoMEX team are also thanked
for numerous attempts to document cells/microbial DNA in Vostok accretion ice samples using different
microscopy and other techniques. SCAR SALEGoS workgroup and its follower the SALE program are
especially grateful for the broadcasting and the attention paid to the SALE studies. Russian Antarctic
Expedition and drillers from Russian Mining Institute are thanked for providing us with ice and frozen
lake water samples. PNPI NRC KI and cryoastrobiology laboratory employees along with undergraduate
students are particularly grateful for the support and possibility of direct participation in the research and
results obtained. The research was supported in part by the Act 211 Government of the Russian Federation,
agreement No. 02.A03.21.0006.
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... The subglacial Lake Vostok (Russian, "east") is the largest, deepest, and most studied lake among more than 400 subglacial lakes (water features) inventoried through airborne radio-echo sounding and satellite altimetry surveys (Siegert et al. 2016;Wright and Siegert 2012). It is located beneath the Russian Vostok Antarctic research station, and it has already been unsealed in triple (Bulat 2016). The naturally refrozen lake water, or accretion, ice collected by deep drilling and used as a proxy for the lake water has proved to be exceptionally clean, though much diluted, leading to controversial biological and chemical analyses. ...
... The lake water (at least the uppermost layer) appears almost entirely lifeless. Only a few bacterial phylotypes were identified in accretion ice, which were not related to contamination (Bulat et al. 2004(Bulat et al. , 2009Bulat 2016). The confidently recorded DNA fingerprint of the chemolithoautotrophic thermophile Hydrogenophilus thermoluteolus suggests the presence of a deep biosphere within the bedrock (Bulat et al. 2004;Petit et al. 2005;Lavire et al. 2006), while the expected high oxygen stress of the water may be very restrictive for biology (Bulat et al. 2004). ...
... Finally, DNA-based techniques including very sensitive DNA amplifications were applied. To validate the DNA results, a contaminant library was established (Bulat et al. 2004;Bulat 2016). ...
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... It was suggested that most DNA sequences from the water of Lake Vostok reported earlier should be considered as contaminants that appeared during the course of the drilling [6]. They emphasized finding the chemolithoautotrophic thermophile bacteria Hydrogenophilus thermoluteolus (Betaproteobacteria), an actinobacterium related to Ilumatobacter fluminis and unclassified bacterium AF532061, which should be considered a true indigenous species of Lake Vostok. ...
... After reaching the surface of the lake at the depth 3769.3 m, later studies in 2012 carried out a metagenomic analysis of DNA isolated from the Vostok ice core [5]. It has been suggested that most DNA sequences from the water of Lake Vostok reported earlier should be considered as contaminants that appeared during the course of the drilling [6]. We report data about the investigation of the water samples independently picked up from Lake Vostok in 2018. ...
... Two previous studies had focused on the molecular characterization of Lake Vostok [5,6]. The authors revealed a great variety of genome fragments belonging to different kingdoms of living organisms, for example, Eubacteria, Archaea, Fungi, Viridiplantae (chloroplasts), and even Metazoa (family Copepoda). ...
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Lake Vostok is the deepest lake of Antarctica but has poor accessibility for study due to a thick glacial cover, however, water samples of this lake have become available for study just recently. Previously, only the microbiome of the ice cover samples was characterized. Here we report results of bacteriological seeding with subsequent identification of the heterotrophic microorganisms (bacteria and micellar fungi) present by 16S rDNA sequencing as well as results of a direct molecular study of the water microbiome. Surprisingly, the data obtained gave evidence of a predominant occurrence of common chemoorganotrophs that were rather psychrotolerant than psychrophilic. We isolated and described strains belonging to eight heterotrophic microbial species able to grow in a rich medium: six bacterial strains belonging to the species Microbacterium testaceum and Microbacterium trichothecenolyticum, Brevundimonas diminuta, Sphingomonas oligophenolica, Sphingomonas sp. and Sphingobium limneticum; and two fungal strains belonging to Dendryphion sp. and Cladosporium fusiforme. Direct study of 16S rDNA purified water samples confirmed the predominance of the Brevundimonas, Microbacterium, Bradyrhizobium, and Bacillus (Bacillus cereus) genera.
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... Thermophiles detected in cold marine and terrestrial habitats span several phyla across the tree of life, with both Bacteria and Archaea (Table 1). Recent 16S rRNA gene sequencing studies have uncovered a number of putative thermophiles in icy [4][5][6][7] and permafrost environments [8][9][10][11], permanently cold (−2 • C to +4 • C) ocean sediments [12][13][14][15][16][17][18][19], and in cool soils with temperatures never exceeding 25 • C [20][21][22][23][24][25] (Figure 1). ...
... Indeed, Lake Vostok is a tectonically controlled subglacial lake with recently recorded minor tectonic activity. The hydrothermal plumes caused by episodic seismotectonic activity in deep faults in the bedrock of the lake could release sediments along with microbial cells from faults towards vents in the freezing zone, where the microbes may have been entrapped in the ice in course of accretion [4][5][6]. The cultivation and recovery of viable Hydrogenophilus spp. ...
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New detections of thermophiles in psychrobiotic (i.e., bearing cold-tolerant life forms) marine and terrestrial habitats including Arctic marine sediments, Antarctic accretion ice, permafrost, and elsewhere are continually being reported. These microorganisms present great opportunities for microbial ecologists to examine biogeographical processes for spore-formers and non-spore-formers alike, including dispersal histories connecting warm and cold biospheres. In this review, we examine different examples of thermophiles in cryobiotic locations, and highlight exploration of thermophiles at cold temperatures under laboratory conditions. The survival of thermophiles in psychrobiotic environments provokes novel considerations of physiological and molecular mechanisms underlying natural cryopreservation of microorganisms. Cultures of thermophiles maintained at low temperature may serve as a non-sporulating laboratory model for further exploration of metabolic potential of thermophiles at psychrobiotic temperatures, as well as for elucidating molecular mechanisms behind natural preservation and adaptation to psychrobiotic environments. These investigations are highly relevant for the search for life on other cold and icy planets in the Solar System, such as Mars, Europa and Enceladus.
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... The identification and characterization of subglacial lakes and their dynamics have largely come from remote geophysical observations 12,26,44,[49][50][51] (Fig. 2a), owing to the challenge of directly accessing and cleanly sampling water and sediments beneath thick ice 52 . Whillans Subglacial Lake 1,53,54 and Mercer Subglacial Lake 55 in West Antarctica (with ice thicknesses of approximately 600 m and 1,100 m, respectively) and western Skaftá Lake 56 and Lake Grímsvötn 57 in Iceland (with ice thicknesses of approximately 400 m and 300 m, respectively) have been cleanly accessed by drilling, while Lake Vostok in East Antarctica (with ice thickness of approximately 4,000 m) has been drilled but the samples obtained were contaminated 58 . In the French Alps, the geometry and water level of a small subglacial lake under Glacier de Tête Rousse (with ice thickness of 76 m) was successfully accessed and monitored using boreholes and sonar 59 . ...
... Substantially less is known about the deep, closed-basin lakes under the thick (>1 km) interior of ice sheets, although they are also anticipated to host ecosystems, owing to possible geothermal stirring of nutrients 107 and inputs of oxygen derived from sediments and/or the ice above. Samples of accretion ice above Lake Vostok contained tens to hundreds of DNA-containing cells per millilitre of melt water 202 and, although these numbers are low compared with the approximately 100,000 cells present in the same volume from Whillans Subglacial Lake, uncontaminated samples from Lake Vostok water remain elusive 58 . Regardless, water column samples collected at a discrete depth might not be representative of water body dynamics, as subglacial lakes can be thermally unstable 2 , which drives internal mixing 107 . ...
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... The identification and characterization of subglacial lakes and their dynamics have largely come from remote geophysical observations 12,26,44,[49][50][51] (Fig. 2a), owing to the challenge of directly accessing and cleanly sampling water and sediments beneath thick ice 52 . Whillans Subglacial Lake 1,53,54 and Mercer Subglacial Lake 55 in West Antarctica (with ice thicknesses of approximately 600 m and 1,100 m, respectively) and western Skaftá Lake 56 and Lake Grímsvötn 57 in Iceland (with ice thicknesses of approximately 400 m and 300 m, respectively) have been cleanly accessed by drilling, while Lake Vostok in East Antarctica (with ice thickness of approximately 4,000 m) has been drilled but the samples obtained were contaminated 58 . In the French Alps, the geometry and water level of a small subglacial lake under Glacier de Tête Rousse (with ice thickness of 76 m) was successfully accessed and monitored using boreholes and sonar 59 . ...
... Substantially less is known about the deep, closed-basin lakes under the thick (>1 km) interior of ice sheets, although they are also anticipated to host ecosystems, owing to possible geothermal stirring of nutrients 107 and inputs of oxygen derived from sediments and/or the ice above. Samples of accretion ice above Lake Vostok contained tens to hundreds of DNA-containing cells per millilitre of melt water 202 and, although these numbers are low compared with the approximately 100,000 cells present in the same volume from Whillans Subglacial Lake, uncontaminated samples from Lake Vostok water remain elusive 58 . Regardless, water column samples collected at a discrete depth might not be representative of water body dynamics, as subglacial lakes can be thermally unstable 2 , which drives internal mixing 107 . ...
Subglacial lakes and their changing role in a warming climate
Article
Full-text available
  • Jan 2022
Subglacial lakes store ancient climate records, provide habitats for life, and modulate ice flow, basal hydrology, biogeochemical fluxes and geomorphic activity. In this Review, we construct the first global inventory of subglacial lakes (773 total): 675 from Antarctica (59 newly identified in this study), 64 from Greenland, 2 beneath Devon Ice Cap, 6 beneath Iceland’s ice caps, and 26 from valley glaciers. We use this inventory to evaluate subglacial lake environments, dynamics, and their wider impact on ice flow and sediment transport. Lake behaviour is conditioned by their unique subglacial setting and the hydrologic, dynamic and mass balance regime of the overlying ice mass. We predict that in regions where climate warming causes ice-surface steepening there will be fewer and smaller lakes, but increased activity with higher discharge drainages of shorter duration. Coupling to surface melt and rainfall inputs will modulate fill-drain cycles and seasonally enhance oxic processes. Higher discharges cause large, transient ice-flow accelerations, but might result in overall net slowdown due to development of efficient subglacial drainage. Future subglacial lake research requires new drilling technologies, and the integration of geophysics, satellite monitoring and numerical modelling, which will provide new insight into their wider role in a changing Earth system.
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... The utilization of the scattering characteristics of returned bed echoes, such as the specularity content, trailing bed echoes, the bed-echo coherent index, and bedecho variability, has advanced the quantitative identification of subglacial water and our understanding of subglacial drainage systems [206]. Subglacial lake drilling provides direct access to subglacial lake water and sediment samples, in a process that can extract valuable information on the paleoclimate and paleoenvironment [207,208]. Other geophysical methods, such as active seismic surveys ( Figure 8d) and electromagnetic (EM) approaches, play important roles in revealing the geological and hydrological conditions prevalent in subglacial lakes [209][210][211][212]. [206]; (b) ICESat-2 altimetry coverage of active subglacial lakes in Antarctica [213]; (c) Radargrams of the Antarctic subglacial hydrological environment [214]; (d) The subglacial lake was imaged using seismic data [215]. ...
Geophysics in Antarctic Research: A Bibliometric Analysis
Article
Full-text available
  • Aug 2023
Antarctica is of great importance in terms of global warming, the sustainability of resources, and the conservation of biodiversity. However, due to 99.66% of the continent being covered in ice and snow, geological research and geoscientific study in Antarctica face huge challenges. Geophysical surveys play a crucial role in enhancing comprehension of the fundamental structure of Antarctica. This study used bibliometric analysis to analyze citation data retrieved from the Web of Science for the period from 1982 to 2022 with geophysical research on Antarctica as the topic. According to the analysis results, the amount of Antarctic geophysical research has been steadily growing over the past four decades as related research countries/regions have become increasingly invested in issues pertaining to global warming and sustainability, and international cooperation is in sight. Moreover, based on keyword clustering and an analysis of highly cited papers, six popular research topics have been identified: Antarctic ice sheet instability and sea level change, Southern Ocean and Sea Ice, tectonic activity of the West Antarctic rift system, the paleocontinental rift and reorganization, magmatism and volcanism, and subglacial lakes and subglacial hydrology. This paper provides a detailed overview of these popular research topics and discusses the applications and advantages of the geophysical methods used in each field. Finally, based on keywords regarding abrupt changes, we identify and examine the thematic evolution of the nexus over three consecutive sub-periods (i.e., 1990–1995, 1996–2005, and 2006–2022). The relevance of using geophysics to support numerous and diverse scientific activities in Antarctica becomes very clear after analyzing this set of scientific publications, as is the importance of using multiple geophysical methods (satellite, airborne, surface, and borehole technology) to revolutionize the acquisition of new data in greater detail from inaccessible or hard-to-reach areas. Many of the advances that they have enabled be seen in the Antarctic terrestrial areas (detailed mapping of the geological structures of West and East Antarctica), ice, and snow (tracking glaciers and sea ice, along with the depth and features of ice sheets). These valuable results help identify potential future research opportunities in the field of Antarctic geophysical research and aid academic professionals in keeping up with recent advances.
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... There are more than 700 reported subglacial lakes in Antarctica (Livingstone et al., 2022), three in Iceland under the Vatnajökull glacier (Bjornsson, 2003), two in Greenland (Palmer et al., 2013), and one recently discovered in the Canadian Arctic (Rutishauser et al., 2018). The biological exploration of some of these lakes has begun, namely Lake Vostok (Karl et al., 1999;Priscu et al., 1999;Christner et al., 2001;Bulat, 2016;Gura and Rogers, 2020), Subglacial Lake Whillans (Tulaczyk et al., 2014), Subglacial Lake Mercer in Antarctica (Priscu et al., 2021), and all three Icelandic lakes (Gaidos et al., 2004(Gaidos et al., , 2009Marteinsson et al., 2013). In the cases of Antarctica and Iceland, the data unambiguously point to the presence of active assemblages of bacterial taxa which are distinct from the distribution in the overlying ice or surrounding glaciated terrain (Gaidos et al., 2004(Gaidos et al., , 2009Marteinsson et al., 2013;Achberger et al., 2016). ...
Metagenomic analyses of a microbial assemblage in a subglacial lake beneath the Vatnajökull ice cap, Iceland
Article
Full-text available
  • Mar 2023
Skaftárkatlar are two subglacial lakes located beneath the Vatnajökull ice cap in Iceland associated with geothermal and volcanic activity. Previous studies of these lakes with ribosomal gene (16S rDNA) tag sequencing revealed a limited diversity of bacteria adapted to cold, dark, and nutrient-poor waters. In this study, we present analyses of metagenomes from the lake which give new insights into its microbial ecology. Analyses of the 16S rDNA genes in the metagenomes confirmed the existence of a low-diversity core microbial assemblage in the lake and insights into the potential metabolisms of the dominant members. Seven taxonomic genera, Sulfuricurvum , Sulfurospirillum , Acetobacterium , Pelobacter/Geobacter , Saccharibacteria, Caldisericum , and an unclassified member of Prolixibacteraceae, comprised more than 98% of the rDNA reads in the library. Functional characterisation of the lake metagenomes revealed complete metabolic pathways for sulphur cycling, nitrogen metabolism, carbon fixation via the reverse Krebs cycle, and acetogenesis. These results show that chemolithoautotrophy constitutes the main metabolism in this subglacial ecosystem. This assemblage and its metabolisms are not reflected in enrichment cultures, demonstrating the importance of in situ investigations of this environment.
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... The Antarctic freshwater Lake Vostok is several thousands-years-old, ice-sealed (subglacial) and dark, at subzero temperatures and high pressure, and nutrientdepleted, yet the water of the main basin contains a sparse community of microorganisms (Siegert et al., 2001;Bulat, 2016;Gura and Rogers, 2020). Under these conditions, it is likely that their cells survive in an inactive (or virtually inactive) state for vast time periods, as do those found in some seawater-and brine environments (see below). ...
Water is a preservative of microbes
Article
Full-text available
  • Dec 2021
Water is the cellular milieu, drives all biochemistry within Earth’s biosphere and facilitates microbe‐mediated decay processes. Instead of reviewing these topics, the current article focuses on the activities of water as a preservative—its capacity to maintain the long‐term integrity and viability of microbial cells—and identifies the mechanisms by which this occurs. Water provides for, and maintains, cellular structures; buffers against thermodynamic extremes, at various scales; can mitigate events that are traumatic to the cell membrane, such as desiccation–rehydration, freeze–thawing and thermal shock; prevents microbial dehydration that can otherwise exacerbate oxidative damage; mitigates against biocidal factors (in some circumstances reducing ultraviolet radiation and diluting solute stressors or toxic substances); and is effective at electrostatic screening so prevents damage to the cell by the intense electrostatic fields of some ions. In addition, the water retained in desiccated cells (historically referred to as ‘bound’ water) plays key roles in biomacromolecular structures and their interactions even for fully hydrated cells. Assuming that the components of the cell membrane are chemically stable or at least repairable, and the environment is fairly constant, water molecules can apparently maintain membrane geometries over very long periods provided these configurations represent thermodynamically stable states. The spores and vegetative cells of many microbes survive longer in the presence of vapour‐phase water (at moderate‐to‐high relative humidities) than under more‐arid conditions. There are several mechanisms by which large bodies of water, when cooled during subzero weather conditions remain in a liquid state thus preventing potentially dangerous (freeze–thaw) transitions for their microbiome. Microbial life can be preserved in pure water, freshwater systems, seawater, brines, ice/permafrost, sugar‐rich aqueous milieux and vapour‐phase water according to laboratory‐based studies carried out over periods of years to decades and some natural environments that have yielded cells that are apparently thousands, or even (for hypersaline fluid inclusions of mineralized NaCl) hundreds of millions, of years old. The term preservative has often been restricted to those substances used to extend the shelf life of foods (e.g. sodium benzoate, nitrites and sulphites) or those used to conserve dead organisms, such as ethanol or formaldehyde. For living microorganisms however, the ultimate preservative may actually be water. Implications of this role are discussed with reference to the ecology of halophiles, human pathogens and other microbes; food science; biotechnology; biosignatures for life and other aspects of astrobiology; and the large‐scale release/reactivation of preserved microbes caused by global climate change.
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Planetary Biosecurity: Applying Invasion Science to Prevent Biological Contamination from Space Travel
Article
  • Nov 2021
As plans for space exploration and commercial use expand rapidly, biosecurity measures and risk assessments that inform them must adapt. Sophisticated protocols are required to prevent biological contamination of extraterrestrial environments from Earth and vice versa. Such protocols should be informed by research on biological invasions—human-assisted spread of organisms into novel environments—which has revealed, inter alia, that (1) invasion risk is driven by the timing and frequency of introduction events, whose control requires addressing the least secure human activities associated with organismal transport; (2) invasions and their impacts are difficult to predict, because these phenomena are governed by context dependencies involving traits of the organism and the receiving environment; and (3) early detection and rapid response are crucial for prevention but undermined by taxonomic methods that fail to recognize what is “alien” versus what is native. Collaboration among astrobiologists, invasion biologists, and policymakers could greatly enhance planetary biosecurity protocols.
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Hot-water drilling for exploration of the Antarctic subglacial environments熱水掘削による南極氷床の底面環境探査
Article
  • Jan 2021
Aquatic environments under the Antarctic ice sheet have drawn attention since the discovery of subglacial hydrological systems consisted of lakes and water channels. The ice sheet base is an important boundary, where basal sliding, geothermal heating, erosion and deposition processes take place. Further, basal melting and subshelf ocean circulation are the keys to understand recent mass loss of the ice sheet. Despite its importance, however, in-situ observation of the subglacial environment is difficult because of the ice cover with a thickness ranging from several hundred meters to several kilometers. Hot-water drilling and borehole measurement techniques are the solutions for the direct observation. In this contribution, we review hot-water drilling and subglacial measurements previously performed in Antarctica. We also introduce our project at Langhovde Glacier as an example of hot-water drilling on an Antarctic outlet glacier, and discuss the future of subglacial exploration of the ice sheet.
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Antarctic subglacial lake exploration: First results and future plans
Article
Full-text available
After more than a decade of planning, three attempts were made in 2012-2013 to access, measure in situ properties and directly sample subglacial Antarctic lake environments. First, Russian scientists drilled into the top of Lake Vostok, allowing lake water to infiltrate, and freeze within, the lower part of the ice-core borehole, from which further coring would recover a frozen sample of surface lake water. Second, UK engineers tried unsuccessfully to deploy a clean-access hot-water drill, to sample the water column and sediments of subglacial Lake Ellsworth. Third, a US mission successfully drilled cleanly into subglacial Lake Whillans, a shallow hydraulically active lake at the coastal margin of West Antarctica, obtaining samples that would later be used to prove the existence of microbial life and active biogeochemical cycling beneath the ice sheet. This article summarizes the results of these programmes in terms of the scientific results obtained, the operational knowledge gained and the engineering challenges revealed, to collate what is known about Antarctic subglacial environments and how to explore them in future. While results from Lake Whillans testify to subglacial lakes as being viable biological habitats, the engineering challenges to explore deeper more isolated lakes where unique microorganisms and climate records may be found, as exemplified in the Lake Ellsworth and Vostok missions, are considerable. Through international cooperation, and by using equipment and knowledge of the existing subglacial lake exploration programmes, it is possible that such environments could be explored thoroughly, and at numerous sites, in the near future.
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PROSPECTS FOR LIFE IN THE SUBGLACIAL LAKE VOSTOK, EAST ANTARCTICA
Article
Full-text available
  • Nov 2015
The objective was to estimate the genuine microbial content of ice samples from refrozen water (accretion ice) from the subglacialLakeVostok(Antarctica) buried beneath the 4-km thick East Antarctic ice sheet as well as surface snow nearby Vostok station. The lake ice samples were extracted by heavy deep ice drilling from3764 mbelow the surface reaching the depth3769.3 mby February 2011 (lake entering). High pressure, an ultra low carbon and chemical content, isolation, complete darkness and the probable excess of oxygen in water for millions of years characterize this extreme environment. A decontamination protocol was first applied to samples selected for the absence of cracks to remove the outer part contaminated by handling and drilling fluid. Preliminary indications showed the accretion ice samples to be almost gas free with the very low impurity content. Flow cytometry showed the very low unevenly distributed biomass in both accretion (0–19 cells per ml) and glacier (0–24 cells per ml) ice and surface snow (0–0.02 cells per ml) as well while repeated microscopic observations were unsuccessful meaning that the whole Central East Antarctic ice sheet seems to be microbial cell-free.We used strategies of Ancient DNA research that include establishing contaminant databases and criteria to validate the amplification results. To date, positive results that passed the artifacts and contaminant databases have been obtained for a few bacterial phylotypes only in accretion ice samples featured by some bedrock sediments. Amongst them are the chemolithoautotrophic thermophile Hydrogenophilus thermoluteolus of beta-Proteobacteria, the actinobacterium rather related (95%) to Ilumatobacter luminis and one unclassified phylotype distantly related (92%) to soil-inhabiting uncultured bacteria. Combined with geochemical and geophysical considerations, our results suggest the presence of a deep biosphere, possibly thriving within some active faults of the bedrock encircling the subglacial lake, where the temperature can be as high as 50 oC and in situ hydrogen is probably present. Our approach indicates that the search for life in the subglacialLakeVostok is constrained by a high probability of forward-contamination. Our strategy includes strict decontamination procedures, thorough tracking of contaminants at each step of the analysis and validation of the results along with geophysical and ecological considerations for the lake setting. This may serve to establish a guideline protocol for studying extraterrestrial ice samples.
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On the stability of air clathrate-hydrate crystals in subglacial Lake Vostok, Antarctica
Article
Full-text available
  • Jan 2001
The conditions of air hydrate stability in Lake Vostok are quantified. The upper limit of concentration of O 2 dissolved in the subglacial water is predicted to be 50 times as high as the O 2 concentration in the air-supersaturated perennially ice-covered surface lakes in Antarctica.
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Vostok Subglacial Lake: Details of Russian Plans/Activities for Drilling and Sampling
Article
Full-text available
  • Jan 2011
The Russian Federation has developed a national project involving the drilling and sampling of Vostok Subglacial Lake, East Antarctica. The objective is to explore this extreme icy environment, using a variety of techniques to identify the forms and levels of life that exist there. The project is funded by the Russian Federal Service ROSHYDROMET. In the 2009/2010 season, drilling operations were restarted at a depth of 3559 m via new borehole 5G-2, successfully reaching a new depth of approximately 3650 m. New accretion ice, including the inclusion-rich "thermophile-containing" horizon (around 3608 m) was again recovered and will be studied to assess the previous scenario and findings. In 2010/2011, the drill will carefully continue to deepen the borehole leaving a 10- to 15-m ice cork and will in season 2011/2012 enter the lake, allowing water to rise up dozens of meters within borehole 5G-2 and subsequently freeze. During the same or following season (2012/2013), borehole 5G-2 will be redrilled to acquire rapidly frozen lake water for complex investigations. In the following season, 2013/2014, a special set of strictly decontaminated biophysical instruments, developed at the Petersburg Nuclear Physics Institute, will be lowered into the water body, with a battery of ocean observatory sensors, cameras, fluorimeters-spectrometers, and special water samplers on board several submersible titan modules. Such activities are in line with environmental stewardship in the exploration of unique aquatic environments under the Antarctic ice sheet.
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Brine micro-droplets and solid inclusions in accreted ice from Lake Vostok (East Antarctica)
Article
Full-text available
  • Jun 2005
Lake Vostok, the largest Antarctic sub-glacial lake (14,000 km2), lies beneath nearly 4 km of ice. Sub-glacial geophysical observations and studies of ice accreting at the lake-glacier interface are the only means available to obtain information on the environment and dynamics of this huge water body formed several million years ago. Accretion ice has been studied using high-resolution synchrotron X-Ray micro-fluorescence. For the first time, liquid brine micro-droplets (3-10 mum) are observed, coexisting with large irregular sulfur-rich aggregates (10-800 mum) containing gases and a mixture of very fine particles. Most of these objects are sequestered inside large crystals that grew slowly after ice formation. Their structure and composition support the existence of hydrothermal activity at the lake bottom and the occurrence of haline water pulses carrying fine solid debris and eventually biota from a deeper evaporitic reservoir into the lake.
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Geological nature of subglacial Lake Vostok
Article
Full-text available
  • Apr 2003
Lake Vostok is located at the edge of vast upland of East Antarctic (Precambrian) Crystalline Shield and represents a typical extensionally-induced intracontinental rift zone. Type indicators of rift nature are: width (60-80 km) and length (about 300 km) of the lake depression; several (3-5) kilometers of sediments (modeled from gravity data) infilling the lake graben, considerable amplitudes of faults bounding the lake (up to 2 km in bedrock relief and in excess of 5 km in basement topography), half-graben-like structures (rotated crustal blocks) at flanks of the lake traceable to crustal extension; along-strike segmentation of the depression (the presence of two isolated basins, recognized from seismic and gravity data); knee-shaped spatial configuration of the lake and existence of diagonal fractures (displayed in bedrock topography) normally nascent in conditions of tensional stress. The rift graben of Lake Vostok is considered to be a part (branch) of more spacious rift system, main arm of which stretched from the Prydz Bay trough the Lambert Glacier and the eastern foot of Gamburtsev Mts. to, at least, 110E. This rift system is a result of large-scale extensional event, which occurred in East Antarctica in Late Jurassic - Early Cretaceous prior to East Gondwana break-up. Sedimentary infill of this age is proposed to dominate in Vostok Lake, although postrift, preglacial (Cretaceous - Paleogene) strata can also forms significant part of depositional section. Helium isotopes data give evidence that the Lake Vostok rift is not active. On the other hand, thermophilic bacteria found in accretion ice suggest the possibility of hydrothermal activity in lake bottom. The conduits for warm underwater can be provided by deep crustal faults bordering rift graben. Microseismicity recorded in the area of Lake Vostok suggests the possibility of crustal deformations (likely during more dramatic earthquakes) providing a necessary fault permeability for water seepage from depths (stratal waters?). Lake Vostok seemed to be unique rift-related lake in Central Antarctica, however analyses of available Radarsat and geophysical (gravity and ice thickness) data allow us to suggest the existence of another large and deep (more than 1000 m b.s.l.) subglacial lake at about 82.5S, 18E. Tectonic setting of this lake is very close to that of Lake Vostok and biota ecosystem of two lakes is also expected to be similar.
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DNA signature of thermophilic bacteria from the aged accretion ice of Lake Vostok, Antarctica: implications for searching for life in extreme icy environments
Article
Full-text available
  • Jan 2004
We have used 16S ribosomal genes to estimate the bacterial contents of Lake Vostok accretion ice samples at 3551 m and 3607 m, both containing sediment inclusions and formed 20000–15000 yr ago. Decontamination proved to be a critical issue, and we used stringent ice chemistry-based procedures and comprehensive biological controls in order to restrain contamination. As a result, up to now we have only recognized one 16S rDNA bacterial phylotype with confident relevance to the lake environment. It was found in one sample at 3607 m depth and represents the extant thermophilic facultative chemolithoautotroph Hydrogenophilus thermoluteolus of beta-Proteobacteria, and until now had only been found in hot springs. No confident findings were detected in the sample at 3551 m, and all other phylotypes revealed (a total of 16 phylotypes, 336 clones including controls) are presumed to be contaminants. It seems that the Lake Vostok accretion ice is actually microbe-free, indicating that the water body should also be hosting a highly sparse life. The message of thermophilic bacteria suggests that a geothermal system exists beneath the cold water body of Lake Vostok, what is supported by the geological setting, the long-term seismotectonic evidence from 4He degassing and the ‘18O shift’ of the Vostok accretion ice. The seismotectonic activity that seems to operate in deep faults beneath the lake could sustain thermophilic chemolithoautotrophic microbial communities. Such a primary production scenario for Lake Vostok may have relevance for icy planets and the approaches used for estimating microbial contents in accretion ice are clearly relevant for searching for extraterrestrial life.
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Technological aspects of the final phase of drilling borehole 5G and unsealing Vostok Subglacial Lake, East Antarctica
Article
  • Sep 2014
. This paper considers the state of the deep ice borehole 5G at the Russian Antarctic Vostok station after penetration to the surface water of Vostok Subglacial Lake. It discusses the peculiar features of drilling the 'fresh frozen' lake water that has risen in the borehole and the technology for subsequent study of the lake water layer via borehole 5G filled with a kerosene–Freon® mixture. The extremely high rise of lake water via the borehole is attributed to a hydraulic fracture at the side of the borehole, which diverted a large amount of drilling fluid. The proposed technology for the study of the water layer envisages minimal environmental impact and excludes penetration of any of the kerosene–Freon® mixture to the water layer. This technology has been presented several times at different international forums. There was no critical comment on the Environmental Impact Assessment of the technology at the 37th Antarctic Treaty Consultative Meeting in 2014 and it was adopted for implementation.
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Limnological Conditions in Subglacial Lake Vostok, Antarctica
Article
  • Nov 2006
Subglacial Lake Vostok is located ,4 km beneath the surface of the East Antarctic Ice Sheet and has been isolated from the atmosphere for .15 million yr. Concerns for environmental protection have prevented direct sampling of the lake water thus far. However, an ice core has been retrieved from above the lake in which the bottom ,85 m represents lake water that has accreted (i.e., frozen) to the bottom of the ice sheet. We measured selected constituents within the accretion ice core to predict geomicrobiological conditions within the surface
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