Exploring Subglacial Antarctic Lake Environments

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Exploring Subglacial Antarctic Lake Environments

J. C. Priscu, M. C. Kennicut, R. E. Bell, S. A. Bulat, J. C. Evans Ellis, V. V.

Lukin, Jean-Robert Petit, R.D. Powell, M. J. Siegert, I. Tabacco

To cite this version:

J. C. Priscu, M. C. Kennicut, R. E. Bell, S. A. Bulat, J. C. Evans Ellis, et al.. Exploring Subglacial

Antarctic Lake Environments. Eos, Transactions American Geophysical Union, American Geophysical

Union (AGU), 2005, 86 (20), pp.193 à 197. �10.1029/2005EO200001�. �insu-00374884�

VOLUME 86 NUMBER 20 17 MAY 2005

EOS, TRANSACTIONS, AMERICAN GEOPHYSICAL U N I O N PAGES 1 93-200

Exploring Subglacial Antarctic Lake Environments

PAGES 1 9 3 , 1 9 7

While subglacial lakes have been suspected, and speculated about, for more than 50 years, recent analyses of historical and new data have shown that liquid water environments are c o m m o n beneath the vast Antarctic Ice Sheet. Airborne radar surveys have now docu­

mented more than 145 subglacial lakes, the largest being LakeVostok located 4 km beneath the vast East Antarctic Ice Sheet (Figure 1).

The public and scientists alike have b e e n intrigued by the possibility that these environ­

ments harbor life in conditions not previously studied on our planet. Planning for the ex­

ploration and study of these unique environ­

ments has focused international attention on the challenges presented by the way s c i e n c e is c o n d u c t e d in such settings while providing for environmental protection and stewardship.

Exploration of subglacial environments will require careful and detailed planning, adop­

tion of environmental protocols, and interna­

tional cooperation.

The Subglacial Lake Exploration Group of Specialists (SALEGOS; http://salepo.tamu.edu/

scar_sale) has m a d e significant progress in developing a plan for the study of subglacial lake environments.The Scientific Committee on Antarctic Research (SCAR) established SALEGOS in 2000 as an international group of scientists with backgrounds n e e d e d to address all facets of a possible research program.The group has served as a focal point for organiz­

ing and encouraging international planning for subglacial lake environment exploration.

SALEGOS' overarching scientific objectives to guide subglacial exploration and research are to:

• understand subglacial environments and their impact on the origins, evolution, and m a i n t e n a n c e of life beneath i c e sheets;

• determine the form, distribution, and func­

tioning of biological, c h e m i c a l , and physical systems in subglacial environments, including the sediments, the water, and the overlying i c e ; and

B Y J . C . PRISCU, M . C . KENNICUTT II, R . E . BELL, S. A . BULAT, J . C . ELLIS-EVANS,V V LUKIN, J . - R . PETIT, R . D . POWELL, M . J . SIEGERT, AND I.TABACCO

• recover and d e c i p h e r the climatic informa­

tion c o n t a i n e d in the sediments in lakes and the i c e sheet sealing the lakes.

The plan requires substantial h u m a n and logistical resources over many years.The proposed programmatic time line (Table 1) is driven in large degree by the sampling meth­

odologies n e e d e d and the samples required to c o n d u c t key experiments. While s o m e tech­

nologies require development, others such as remote sensing are already being applied in ongoing studies. More challenging objectives require lake entry and the most challenging objectives require sample retrieval.

The deployment of in situ observatories is o n e possible first step in exploring sub­

glacial lakes, and c a n b e mostly accomplished using current o c e a n o g r a p h i c t e c h n o l o g y Observatories could gather a time series of b a s i c physical and c h e m i c a l measurements

that would b e essential to assist in the plan­

ning for the more c o m p l e x c o m p o n e n t s of the program involving s a m p l e retrieval. The first phase of observatories c o u l d b e static or vertically m o b i l e strings of sensors deployed in multiple locations within a lake.

Sample return will focus on the identity and diversity of life forms in a lake, in situ growth and m e t a b o l i c rates, the p r e s e n c e of unique b i o c h e m i c a l a n d / o r physiological processes, and the evolutionary history of subglacial en­

vironments recorded in lake sedimentary re­

cords. While a major c o m m i t m e n t of resources will b e necessary to implement an ambitious program of exploration and research, the potential scientific and educational payoff is immense.

Chemical, Glaciological, and Geological Properties of Subglacial Lakes

To date, investigations of subglacial lake en­

vironments have b e e n directed at LakeVostok, owing to the e x i s t e n c e of a d e e p b o r e h o l e over the lake. Relatively little is known about other subglacial environments. Energy mass

180°

Fig. 1. Locations of Antarctic subglacial lakes. Highlighted are lakes discovered by Italian (blue

triangles), Russian (red triangles), and U.K.-U.S.-Danish (yellow triangles) teams. Lake Vostok is

shown in outline. The ice sheet surface is contoured at 500-m intervals. Compiled from Siegert et

al. [2005] and T a b a c c o et al. [2003]. Original color image appears at the back of this volume.

Eos, Vol. 86, No. 2 0 , 1 7 May 2005

T a b l e 1. S A L E G O S A s s e s s m e n t o f t h e T i m i n g o f S u b g l a c i a l L a k e E x p l o r a t i o n a n d K e y T e c h n o l o g i c a l M i l e s t o n e s

Time Milestone

Short ( 0 - 3 years)

existing technologies, modeling, and other non- field-related activities Medium

( 3 - 6 years)

lake entry and observa­

tory deployment; possi­

ble sample return from West Antarctic lakes Long

( 6 - 9 years) water/shallow sediment retrieval Very long

(9+ years) sediment deep coring

a

Note that the environmental requirements increase in complexity as the activities increase in complexity.

balance considerations constrain specula­

tion about ice melting and accretion at the lake/ice sheet interface capping LakeVostok.

Ice sheet melting o c c u r s at the northern end of the lake, whereas lake water is freezing to the glacier base over the remainder of the lake surface, resulting in removal of water from the lake by lateral ice sheet motion.

Accreted ice most likely forms by a mecha­

nism similar to frazil ice (which forms from small, randomly oriented spherically crystals that float on water), followed by consolidation via interstitial water freezing. Sediment inclu­

sions in accretion ice are older than 1.5 Ga,and presumably originate from erosional contact of the ice sheet with the surrounding basement rocks.The sedimentary inclusions contain gypsum particles and are enriched in soluble sodium chloride, and magnesium and calcium sulphate, suggesting the presence of an evap- orite deposit upstream of the lake that was em- placed before the onset of Antarctic glaciation

[DeAngelis et al., 2004] .The ionic content of clear, accreted ice is 5 - 5 0 times lower than ob­

served in glacier ice implying that it originates from lake water with a salinity of 0.1 %o or less.

Models of gas hydrate formation and stability predict that the lake water is supersaturated with respect to nitrogen and oxygen. Over­

pressure and high levels of these gases have important practical ramifications for sampling efforts and may limit life in the lake.The physical/chemical properties of water in Lake Vostok inferred from accretion ice analyses and the tilted lake-glacier interface, suggest that thermohaline circulation o c c u r s in the lake. Recent aero-geophysical surveys of Lake Vostok by Russian and U.S. scientists have mapped the lake in great detail, confirming the presence of two basins and morphologi­

cally complex shoreline and basal features.

Circulation, combined with the lake's complex morphology, suggests the likelihood of hori­

zontal and vertical chemical and physical gra­

dients in the waters within the lake.The latest estimates of the residence time of water in Lake Vostok vary widely between 13,000 and 80,000 years [Petit etal, 2003, Studinger etal, 2004].

Life Beneath the Ice

Probably the most tantalizing, and the most controversial, studies c o n c e r n the likelihood of life in Lake Vostok. Studies of bacterial isolates and DNA clones ( a section of DNA that has been inserted into a vector molecule, such as a plasmid or a phage chromosome, and then replicated to form many identical copies) recovered from accreted ice have been used to infer the presence of life in the lake. Microbiological studies have shown how microbes might make a living and what the

"seed" populations might be that established life in these dark, cold, high-pressure, and ultra- low nutrient level environments.

The nature of the samples, the unknowns of how the accretion process fractionates com­

ponents from its source waters, the integrity of microbes in these settings over long time periods, the possibility of contamination from the drilling and recovery processes, the very dilute biological solutions, and the limited avail­

ability of the samples all suggest that caution should be exercised when interpreting these preliminary results.

Not unexpectedly these limitations have led to differing opinions and, in some cases, contradictory results.While the origins of the microbes isolated from a c c r e t e d ice are difficult to ascertain unequivocally, s o m e of them may originate from contamination during the sample collection, retrieval and processing procedures and some appear to be indigenous to the ice (or the lake) [Priscu and Christner, 2 0 0 4 ] . DNA signatures indicate that ice-entombed microbes include phylotypes similar to known thermophilic and yet unclas­

sified phylotypes [Bulat et al, 2004] as well as mesophilic bacteria with diverse physiologies and different habitat preferences, including a hot spring [Priscu et al, 1999; Karl et al, 1999;

Christner etal, 2 0 0 1 ] .

Fundamental to lake ecosystem processes is the ability of organisms to survive and func­

tion within these unusually dilute chemical environments. On the basis of varying and limited evidence, researchers have arrived at differing conclusions.An intriguing question is whether alternative sources of energy, such as geothermal inputs, are present in subglacial environments.The geochemical composition of the a c c r e t e d ice samples has been inter­

preted as indicating a hydrothermal contribu­

tion to LakeVostok with a source somewhere upstream from the Vostok drill site [Souchez et al, 2 0 0 3 ] . Resolution of this question awaits more direct evidence that c a n only be ob­

tained from lake sampling.

The Latest Developments

Recent developments include a proposal by Russian and French scientists to select a site and drill a deep hole above the northern part of LakeVostok in the time frame of the International Polar Year (IPY) 2 0 0 7 - 2 0 0 8 ; a provocative suggestion of a second large lake in East Antarctica [Leitchenkov etal, 2 0 0 3 ] ; intriguing details of ice accretion and melting dynamics discovered by Italian scientists in subglacial systems at Dome-C, located on the

east Antarctic plateau approximately 5 6 0 km from LakeVostok [Tabacco etal, 2 0 0 3 ] ; a n d expansion of the inventory of subglacial lakes to 145 features [Siegert et al, in press].

Scientists from the United Kingdom now have evidence supporting the existence of Lake Ellsworth, a subglacial lake in West Antarctica, from radar sounding of the lake surface and numerical modeling of the ice sheet thermal regime [Siegert et al, 2 0 0 4 ] . The British Antarctic Survey acquired new transects over the lake in the austral summer of 2 0 0 4 - 2 0 0 5 , which confirm the position of the lake across the subglacial foothills of the Ellsworth Mountains.

A U.K.-led team of over 25 scientists, from 12 institutions and five nations, met for the third time at the British Antarctic Survey during March 2005.The purpose of the meeting was to plan in situ exploration of Lake Ellsworth; a proposal to secure funding for the first steps of exploration, geophysical surveys for the lake, has been tentatively approved and awaits scheduling (www.ggybris.ac.uk/ellsworth).

At its 28th Meeting in Bremerhaven, Germa­

ny (October 2 0 0 4 ) , t h e Scientific Committee on Antarctic Research designated Subglacial Antarctic Lake Environments (SALE) as a ma­

jor Scientific Research Program (Eos, 86(9), 90, 2005; http://vpr-zope.tamu.edu/scar_sale). An Expression of Intent entitled the "SALE - Uni­

fied International Team for Exploration and Discovery (SALE-UNITED)"was identified by the International Council of Science (ISCU)/

World Meteorological Organization ( W M O ) J o i n t C o m m i t t e e for the IPY 2 0 0 7 - 2 0 0 8 as a potential"core"program during IPY 2 0 0 7 - 2 0 0 8 (http://salepo.tamu.edu/sale_united). Finally a U.S.-SALE program and office have recently been formed to organize and coordinate U.S.

interests in this area (contact m-kennicutt@

tamu.edu, http://vpr-zope.tamu. edu/us_sale).

References

Bulat,S.A.,et al. (2004),DNA signature of thermophilic bacteria from the aged accretion ice of LakeVostok, Antarctica: Implications for searching for life in extreme icy environments,Int. J. Astrobioi, 5 ( 1 ) , 1-12.

Christner, B. C , E. Mosley-Thompson, L. G.Thompson, and J. N. Reeve ( 2 0 0 1 ) , Isolation of b a c t e r i a and 16S rDNAs from LakeVostok a c c r e t i o n i c e , E n v i r o n . Microbiol, 3, 5 7 0 - 5 7 7 .

De Angelis, M., J.-R. Petit, J. Savarino, R. Souchez, and M.H.Thiemens ( 2 0 0 4 ) , Contribution of an ancient evaporitic-type reservoir to Lake Vostok chemistry, Earth Planet. Sci. Lett., 222, 7 5 1 - 7 6 5 .

Karl, D. M., D.FBird, K. B j o r k m a n J . Houlihan, R.Shackelford,and L.Tupas ( 1 9 9 9 ) , M i c r o o r g a n ­ isms in the a c c r e t e d ice of Lake Vostok, Antarctica, Science, 286, 2 1 4 4 - 2 1 4 7 .

Leitchenkov, G. L.,V N. MasoloyV V Lukin, S. A. Bulat, R. G. Kurinin, and V Y Lipenkov ( 2 0 0 3 ) , Geological nature of subglacial Lake Vostok, paper presented at the EGS-AGU-EUG Joint Assembly, Nice, France, 6 - 1 1 April.

Petit, J. R.,M. Blot, and S. Bulat ( 2 0 0 3 ) , L a c Vostok, a la d e c o u v e r t e d'un environnement sous glaciaire et de son c o n t e n u biologique, in Environnement de la Terre Primitive, edited by M. Gargaud and J. P Parisot, pp. 2 7 3 - 3 1 6 , Presses Univ. d e B o r d e a u x , B o r d e a u x , France.

Priscu, J . C , a n d B.Christner ( 2 0 0 4 ) , E a r t h ' s icy biosphere, in Microbial Diversity and Prospecting, edited by A.T. Bull, pp. 1 3 0 - 1 4 5 , Am. Soc. of Micro­

biol. Press, Washington, D. C.

P r i s c u , J . C . , e t al. ( 1 9 9 9 ) , G e o m i c r o b i o l o g y of subgla­

cial i c e a b o v e Lake Vostok, Antarctica, Science, 286, 2 1 4 1 - 2 1 4 3 .

Siegert, M. J., R. Hindmarsh H. Corr, A. Smith, J.Wood­

ward, E. C . K i n g , A . J . P a y n e a n d I.Joughin ( 2 0 0 4 ) , S u b g l a c i a l Lake Ellsworth: A c a n d i d a t e for in situ exploration in West Antarctica, Geophys. Res. Lett, 3 7 ( 2 3 ) , L 2 3 4 0 3 , d o i : 1 0 . 1 0 2 9 / 2 0 0 4 G L 0 2 1 4 7 7 . Siegert, M. J . , S . Carter, I . T a b a c c o , S. Popov, a n d D. Blan-

kenship ( 2 0 0 5 ) , A revised inventory of Antarctic s u b g l a c i a l lakes, Antarctic Sci., in press.

S o u c h e z , R., J. R. Petit, J. J o u z e l , M. DeAngelis, a n d J . Tison ( 2 0 0 3 ) , Re-assessing lakeVostok's b e h a v i o r from existing a n d n e w i c e c o r e data, Earth Planet.

Sci. Lett., 217, 1 6 3 - 1 7 0 .

R. E. Bell, Lamont-Doherty Earth Observatory, Pali­

s a d e s , N.Y; S. A. Bulat, Division of Molecular a n d Radia­

tion Biophysics, Petersburg Nuclear Physics Institute, St. Petersburg, Russia; J. C. Ellis-Evans, British Antarctic Survey Cambridge, U.K.;VVLukin,Arctic a n d Antarctic R e s e a r c h Institute, St. Petersburg, Russia; J.-R. Petit, LGGE, Centre National de la R e c h e r c h e Scientifique (CNRS), Cedex,France; R. D. Powell, Northern Illinois University,DeKalb; M.J.Siegert,Bristol Glaciology Center, S c h o o l of Geographical S c i e n c e s , University of Bristol, U.K.; a n d I.Tabacco, DST-Geofica, Milan, Italy

For additional information,contact J.C.Priscu; E-mail:

j p r i s c u @ m o n t a n a . e d u .

MEETINGS

Paleoceanography and Paleoclimatology of the Southern Ocean

PAGES 1 9 3 , 1 9 5

Among the greatest s u c c e s s e s of the Ocean Drilling Program were the c o n c e r t e d drilling efforts and exciting results recovered from the Southern Ocean (SO) surrounding Antarctica.

Scientific drilling in the SO and on the Antarctic margin has recovered material from hundreds of sites for scientific analysis.The dynamic na­

ture of i c e sheet development and ice/margin interactions through time has b e e n observed, as has the role that the SO plays in the develop­

ment and persistence of Antarctic glaciation.

The SO has been documented as a sensitive mixing pool of global water masses that is at times a locus of high biological sedimentation.

Also, the SO has b e e n found to contain high-res­

olution records of climate forcing and response, and as such it may hold clues to future climate.

T h e s e results from scientific drilling over the past several d e c a d e s have significantly increased the understanding of C e n o z o i c to d e c a d a l processes affecting o c e a n o g r a p h y and climatology of the SO and Antarctica. Now, it is important to mine these results from sci­

entific drilling over the past several d e c a d e s , and also to provide a scientific, framework for future expeditions in this region to solve unan­

swered questions. What, for example, was the role of iron as a biolimiting nutrient through time? How d o e s s e a i c e c o v e r relate to ventila­

tion of the SO and thus to gas fluxes of c a r b o n dioxide on glacial timescales? Was Antarctic glaciation related to the opening of o c e a n gateways, to d e c r e a s e s in atmospheric c a r b o n dioxide, or to s o m e other factor?

To this end, 26 researchers from five coun­

tries attended a synthesis workshop on the c a m p u s of the University of Colorado, Boulder, in J a n u a r y The workshop, funded by the U.S.

S c i e n c e Support Program of Joint O c e a n o - graphic Institutions, Inc., focused on Southern O c e a n p a l e o c e a n o g r a p h y and paleoclima­

tology It began with plenary overview talks about the critical aspects of SO development, and continued with poster presentations and discussions in breakout groups, by the group as a whole, and over social events.

The underlying t h e m e s of the discussions fo­

cused on extracting what is and is not known about a n u m b e r of critical processes, includ­

ing i c e sheet development, tectonics, ecosys­

tem dynamics, b i o g e o c h e m i c a l responses, and SO thermal structure, on various timescales.

After the discussions, what s e e m e d like a good idea before the workshop (i.e.,conducting a synthesis workshop on a regional or topical t h e m e ) now s e e m s a must-do for a number of fields related to scientific drilling. Although often the push to recover more samples from critical p l a c e s is what necessarily drives much of the s c i e n c e , workshop attendees agreed that mining the physical and intellectual ar­

chive left from d e c a d e s of scientific drilling results is also an important activity that should b e e n c o u r a g e d and funded as a priority mis­

sion of the program.

As summarized by the plenary speakers, several decades worth of scientific drilling in the sea and on land have provided many answers and questions. Peter Barker (British Antarctic Survey) presented the Cenozoic context to SO develop­

ment, with several aspects of Antarctic glaciation that are well-known: (1) Significant glaciation started - 3 4 Ma, and cooling intensified from 16 to 13 Ma and in the late Pliocene; (2) except for glacial/interglacial changes there has likely been little change over the past 9-10 Myr in Antarctic ice sheet volume; and (3) atmospheric carbon dioxide is not the whole answer to Antarctic glacial history Several important questions were also presented:

(1) How glaciated was Antarctica during the Oli- gocene,and how deglaciated was it during the early Miocene? ( 2 ) What caused end-Oligocene warming and mid-Miocene cooling? (3) How did high-latitude cooling operate before glaciation?

In addition, Barker focused on the develop­

ment of the Antarctic Circumpolar Current (ACC),noting that: ( 1 ) ACC transport o c c u r s in narrow but meandering frontal jets, ( 2 ) the ACC may not have c a u s e d glaciation, and ( 3 ) increased primary production a l o n e is not a safe ACC indicator. Several unanswered ques­

tions remain: ( 1 ) When did a deep-reaching ACC begin? ( 2 ) How did the ACC evolve? ( 3 ) What was SO circulation before the ACC?

Carlota Escutia (University of Grenada) focused on geomorphology and i c e dynam­

ics in Antarctica, highlighting an Integrated O c e a n Drilling Program (IODP) proposal to drill the Antarctic Wilkes Land margin.The Wil­

kes Land is the only known Antarctic margin where the unconformity separating pre-glacial strata b e l o w from glacial strata above in the continental shelf c a n b e traced to the abyssal plain, allowing s e q u e n c e s to b e linked. Be­

c a u s e strata b e l o w and above the "glacial on­

set" unconformity c a n b e sampled at relatively shallow depths, the record of the onset of glaciation c a n b e obtained from ( 1 ) the shelf foreset section, which provides a direct record of o c c u r r e n c e of grounded ice but o n e that is less continuous and hard to date, and ( 2 ) the abyssal plain hemipelagic (distal continental s e d i m e n t ) section, which provides an indirect record of glaciation but o n e that is more c o n ­ tinuous and easier to date.

Kathy Licht (Indiana University-Purdue Uni­

versity Indianapolis) discussed the dynamics of ice-sediment interactions from Antarctica to the SO from the Last Glacial Maximum (LGM) to the present. S h e reported that LGM condi­

tions in Antarctica are reasonably well c o n ­ strained—for example, i c e sheet extent is well defined in most p l a c e s and indicates that an equilibrium configuration was not achieved.

Deglaciation records to date show that the i c e sheet did not retreat until well after 18 k a , a n d therefore had a c o m p l e x response to global s e a level rise. Additionally, chronological data of the i c e marginal positions do not show evi­

d e n c e of catastrophic retreat of the West Ant­

arctic i c e sheet in the Ross Sea. Licht noted that several aspects of ice-sediment dynamics are not as well known, most notably the fate of sedi­

ment transported to the continental slope and the role of ice shelves; these unknowns reduce the certainty about the relationship between ice margin fluctuations and SO sedimentation.

Bernard Diekmann (Alfred Wegener Insti­

tute Potsdam) presented a summary of Pleisto­

c e n e sedimentation patterns in the SO. During glacial stages, the locus of prominent opal deposition is shifted to the north in response to a wider extension of seasonal s e a i c e and a displacement of the polar front to the north, but little quantitative data and proxies exist for calculating the spatial and temporal mass budget of opal deposition.Terrigenous (conti- nentally-derived) fluxes are mostly e n h a n c e d during glacial stages, particularly in the Atlan­

tic s e c t o r of the SO, but little quantitative infor­

mation is available to assess the individual ef­

fects of stronger glacial input, eolian s e d i m e n t S t u d i n g e r , M . , R . E . B e l l , a n d A.A.Tikku ( 2 0 0 4 ) ,

Estimating the depth a n d s h a p e of subglacial Lake Vostok's water cavity from aerogravity data, Geophys. Res. Lett, 31, L 1 2 4 0 1 , d o i : 1 0 1 0 2 9 / 2 0 0 4 G L 0 1 9 8 0 1 .

T a b a c c o , I., E. A. Forieri, A. Delia Vedova, A. Zirizzotti, C. B i a n c h i , P D e Michelis, a n d A. Passerini ( 2 0 0 3 ) , E v i d e n c e of 14 n e w s u b g l a c i a l lakes in D o m e C-Vostok area, Terra Antarct. Rep., 8, 1 7 5 - 1 7 9 . Author Information

J. C. Priscu, D e p a r t m e n t o f Land R e s o u r c e s a n d En­

vironmental S c i e n c e s , M o n t a n a State University, Boz-

e m a n ; M.C.Kennicutt II, Office of the Vice President

for R e s e a r c h , T e x a s A&M University College Station;

Eos, Vol. 86, No. 2 0 , 1 7 May 2005