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Future Directions in Subglacial Environments Research
M. C. Kennicut, Jean-Robert Petit
To cite this version:
M. C. Kennicut, Jean-Robert Petit. Future Directions in Subglacial Environments Research. Eos,
Transactions American Geophysical Union, American Geophysical Union (AGU), 2007, 88 (11), 1 à ?
p. �10.1029/2007EO110002�. �insu-00376339�
Vol. 88, No. 11, 13 March 2007
Future Directions in Subglacial Environments Research
PAGES 1 2 9 , 1 3 1
Subglacial Antarctic Lake Environments (SALE) exploration and study is poised to b e a major focus of Antarctic s c i e n c e for the next d e c a d e or more. The foundation for an inten
sive period of SALE research and field efforts has b e e n provided by substantial improvement in our understanding of these environments, the establishment of SALE research programs by the International Polar Year (IPY) Program Office and the Scientific Committee on Antarc
tic Research (SCAR), the funding of several national SALE programs, independent guid
a n c e on environmental stewardship issues, and a series of international workshops, meet
ings, and conferences that have refined SALE scientific objectives. This article summarizes recent developments in subglacial environ
ment exploration and study and describes future research needs.
The Fundamentals of SALE Science In the 7 years s i n c e the report "Subglacial Lake Exploration: W o r k s h o p and R e c o m mendations" (SCAR International Workshop, Cambridge, U.K., S e p t e m b e r 1999), our understanding of subglacial environments h a s greatly improved. Subglacial environ
ments are c o n t i n e n t a l - s c a l e p h e n o m e n a that o c c u r under thick i c e s h e e t s [Siegert et al, 2 0 0 5 ] . T h e i m p o r t a n c e and role of subglacial water are now r e c o g n i z e d a s central to many p r o c e s s e s that have s h a p e d the Antarctic continent and its i c e s h e e t s today and in the past. Subglacial environments include a range of features that differ in g e o l o g i c set
ting, age, evolutionary history, limnological conditions, and size [Bell, 2 0 0 6 ] . T h e s e envi
ronments are 'natural' Earth-bound m a c r o c o s m s that in s o m e i n s t a n c e s t r a c e their ori
gins to a time before A n t a r c t i c a b e c a m e e n c a s e d in i c e [Bell, 2 0 0 6 ] .
Subglacial environments a r e isolated from the weather, the s e a s o n s , a n d celestially con
trolled climatic c h a n g e s that establish funda
mental constraints o n the structure and functioning of most o t h e r Earth-bound envi
ronments. In contrast to t h e s e other habitats, w h e r e solar energy is a primary influence, p r o c e s s e s in subglacial environments a r e mediated by the flow of the overlying i c e , a glaciological b o u n d a r y condition, and the flux of heat and possibly fluids from the underlying basin, a t e c t o n i c control. R e c e n t findings suggest that a third control is sub
glacial hydrology, w h i c h establishes water r e s i d e n c e time and e n a b l e s the delivery of water, materials, and heat to a n d through subglacial systems.
B Y M . KENNICUTT II AND J.-R. PETIT
T h e s p e c t r u m of types of below-ice envi
ronments that o c c u r a c r o s s the Antarctic continent provides an unparalleled opportu
nity to e x p l o r e a n d study o n e of Earth's last frontiers and d e c i p h e r fundamental Earth and life p r o c e s s e s . T h e exploration and study of subglacial environments will a d v a n c e our understanding of how life, cli
mate, and planetary history have c o m b i n e d to produce the Antarctic continent as w e know it today.
Life Beneath the Ice
A first-order question is whether microbial life is present in t h e s e environments. Subgla
cial environments may c o n t a i n a n c i e n t ecosystems, and most e v i d e n c e suggests that the a b s e n c e of life would b e more unex
p e c t e d than its p r e s e n c e . Darkness and isola
tion limit the potential m o d e s of primary pro
duction in subglacial environments. B e c a u s e of a lack of direct inputs of solar energy, microbial metabolism in these systems would rely on metabolic energy and nutrition derived from glacial ice, the b e d r o c k , and/or hydrothermal or geothermal inputs.
An influx of hydrothermal and/or geother
mal heat and c h e m i c a l s would have a pro
found impact on subglacial microbiology.
Whether these environments are 'open' or 'closed' will also b e critically important to
their ability to sustain life, as c a r b o n and energy may b e limiting. For e x a m p l e , are there e x c h a n g e s a m o n g lakes that deliver nutrients and 'microbial s e e d populations'? If so, on what time frames do t h e s e e x c h a n g e s o c c u r ? 'Interconnectedness' will exert a fun
damental influence on subglacial physical and c h e m i c a l characteristics and the c a p a c ity of these environments to support life.
As with surface lakes, stability over time will b e a determinant of the kinds of e c o s y s tems that might b e present. T h e size, l o c a tion, and a g e of below-ice water a c c u m u l a tions are a l s o critical determinants of the physical, c h e m i c a l , and e c o l o g i c a l c h a r a c teristics of subglacial water a n d s e d i m e n t c o l u m n s . Models of lake water circulation;
quantitative water, heat, and b i o c h e m i c a l budgets; estimates of water age; a n d m e a surement of p h y s i c o c h e m i c a l distributions in water and s e d i m e n t s a r e n e e d e d to fully d e s c r i b e subglacial environments.
If life is detected, it will b e important to determine the biomass, distribution, and diversity of organisms in subglacial water col
umns, sediments, and ice. T h e distribution of bioactive elements in these systems will also indicate whether microbiological communi
ties are, or have b e e n , present. T h e m e t a b o l i c and physiological abilities of subglacial resi
dents will lend clues to adaptive strategies for survival and persistence. To unambiguously determine the p r e s e n c e of life in t h e s e unique environments, protocols are n e e d e d to detect life in highly oligotrophic environments and to recover contaminant-and artifact-free sam
ples. T h e retrieval and analysis of s a m p l e s at
in situ conditions also presents significant
technological challenges.
Eos, Vol. 88, No. 11, 13 March 2007
Sub-Ice Hydrology
T h e distribution of subglacial lakes b e n e a t h i c e s h e e t s suggests that hydrologic p r o c e s s e s play an important role at the b a s a l interface of i c e s h e e t s [Wingham et al, 2 0 0 6 ; Clarke, 2 0 0 6 ] . T h e r e is increasing e v i d e n c e that t h e s e environments are c o n n e c t e d by below-ice hydrologic systems, a n d r e c e n t observations suggest that subglacial lakes are linked to the onset of ice s t r e a m s influ
e n c i n g the d y n a m i c s of overlying i c e s h e e t s [Siegert and Bamber, 2002; Wingham et al, 2 0 0 6 ] (Figure 1).
T h e geographic distribution of subglacial lakes is foremost determined by the avail
ability of water and basins for it to c o l l e c t in.
It has b e e n o b s e r v e d that subglacial lakes are usually l o c a t e d within 100 kilometers of ice divides. Other controls on the distribu
tion of liquid, below-ice water include sur
face temperatures, accumulation rates, i c e t h i c k n e s s , i c e velocities, and hydrothermal/
g e o t h e r m a l fluxes. An understanding of sub
glacial hydrology on a continental s c a l e is n e e d e d to establish subglacial water distri
bution and the effects of subglacial water m o v e m e n t s on the overlying i c e sheet.
T h e c o n n e c t i o n b e t w e e n subglacial lakes and i c e d o m e s is poorly understood, a n d further studies are n e e d e d to explore the sig
nificance of this a s s o c i a t i o n . T h e spatial a n d temporal distribution of free water at the i c e b e d , rates of water and sediment transport through subglacial environments, and quan
tification of ice s h e e t interactions with sub
glacial water are n e e d e d to more fully and accurately d e s c r i b e t h e s e systems. Regional geophysical survey results c a n inform mod
els of subglacial drainage and sedimentation over a range of temporal and spatial s c a l e s .
Records of the Past
It has b e e n s p e c u l a t e d that the origins and evolution of subglacial environments are recorded in subglacial sedimentary s e q u e n c e s . Studies of lake s e d i m e n t s in non- glaciated continents have made significant contributions to understanding paleoenvi- ronments. Subglacial lakes are also e x p e c t e d to contain sedimentary records of past c h a n g e s and might b e e x p e c t e d to s h e d light on the C e n o z o i c evolution of the Ant
arctic continent and the a s s o c i a t e d ice sheets. T h e continental geological record of Antarctica's p a l e o c l i m a t e and ice sheet his
tory is currently being addressed by c o r e s from the continent's edges. Few b o r e h o l e s have a c c e s s e d the records stored b e n e a t h Antarctica's i c e sheets. Subglacial s e d i m e n t s would b e e x p e c t e d to record a history of geological p r o c e s s e s occurring at the b a s e of i c e sheets.
The sedimentary records may inform us about the thresholds for ice sheet initiation, the growth and decay rates of ice sheets, c h a n g e s in ice sheet volumes over time, the
nature of the preglacial to subglacial transition, and whether subglacial environments survive glacial/interglacial transitions. Subglacial sedi
ments may also contain a record of how life has evolved in response to these events.
A c o m p l e t e and a c c u r a t e interpretation of t h e s e unique g e o l o g i c a l records will require an understanding of the m e c h a n i s m s that disrupt or destroy stratigraphic c h r o n o l o g i e s in t h e s e settings. Subglacial lake c e s s a t i o n events are e x p e c t e d to have profound effects on the expression of life in t h e s e environ
ments. Chronological tools are n e e d e d to date subglacial lake records and estimate the age of subglacial water a c c u m u l a t i o n s .
Sub-Ice Water as an Agent of Change Emerging e v i d e n c e that Antarctic subgla
cial lakes catastrophically drain and that they are linked to the onset of i c e s t r e a m s suggests that t h e s e features are an integral part of the global c r y o s p h e r e a n d climate system [Lewis et al, 2 0 0 6 ] . Outbursts of fresh water from Antarctic subglacial envi
ronments have b e e n invoked as an agent of landscape c h a n g e in the past, and there is speculation that these discharges influenced past climate. T h e linkage of subglacial lakes with the onset of rapid ice flow indicates that subglacial lakes and the associated hydro- logic systems may b e important factors in the drainage and collapse of ice sheets. Histori
cal records in c o r e s collected around the continental margins will retain a record of the spatial and temporal distribution of outburst deposits and c a n b e used to map onshore and offshore landforms suggestive of erosion due to these flood events. Freshwater inputs and their impact on o c e a n circulation are also e x p e c t e d to b e recorded in the sedimen
tary record. O c e a n i c sensitivity to subglacial hydrological p r o c e s s e s c a n b e tested using models to explore the importance of subgla
cial water in the global climate system.
The Way Forward
Building on many years of discussions and meetings, the scientists and t e c h n o l o gists a s s e m b l e d in Grenoble in 2 0 0 6 laid out an ambitious and exciting plan to a d v a n c e our understanding of subglacial environ
ments. As the central role and i m p o r t a n c e of water b e n e a t h the massive Antarctic i c e s h e e t s have b e e n recognized, the s c o p e of SALE r e s e a r c h has e x p a n d e d to include b a s i c questions a c r o s s a range of scientific disciplines. If the a d v a n c e s of the past few years are an indication of the discoveries and knowledge to c o m e , the study and exploration of subglacial environments hold great promise for furthering our understand
ing of our planet's fifth-largest continent and its i c e sheets, their evolution over g e o l o g i c time, and how t h e s e global forces have influ
e n c e d the expression of life on Earth, and
for lending c l u e s to the p r e s e n c e of life else
where in our solar system.
Acknowledgments
At an international gathering in Grenoble, France, in April 2 0 0 6 , participants presented their latest scientific findings about subgla
cial Antarctic lake environments (see http://
salepo.tamu.edu/saleworkshop2006). T h e group e x p a n d e d plans for future SALE explo
ration and study, c o n c l u d i n g that a conti
nent-wide c a m p a i g n at multiple locations, to (1) systematically m a p subglacial lake sys
tems and their environs and ( 2 ) enter, instru
ment, and s a m p l e i c e , water, sediments, and potential m i c r o b i o l o g i c a l residents, w a s essential to a c c o m p l i s h the interdisciplinary goals of SALE. SALE scientific objectives address fundamental questions about the g e o d y n a m i c s of lake evolution; subglacial hydrology; i c e s h e e t dynamics; microbiologi
c a l life, evolution, a n d adaptation; limnology and b i o g e o c h e m i s t r y ; paleoclimate; and global climate c o n n e c t i o n s . The authors wish to recognize the workshop International and Local Steering Committee and the 84 work
shop attendees. Financial support for the work
shop was provided by the U.S. National Sci
e n c e Foundation Office of Polar Programs, the Scientific Committee on Antarctic Research (SCAR), and the Centre National de la Recher
c h e Scientifique (CNRS).
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