Large subglacial lake beneath the Laurentide Ice Sheet inferred from
sedimentary sequences
Poul Christoffersen Scott Polar Research Institute, University of Cambridge, Cambridge CB2 1ER, UK
Slawek Tulaczyk Earth and Planetary Sciences Department, University of California–Santa Cruz, Santa Cruz, California 95064, USA
Nigel J. Wattrus Large Lakes Observatory and Department of Geological Sciences, University of Minnesota–Duluth, Duluth,
Minnesota 55812, USA
Justin Peterson
Earth and Planetary Sciences Department, University of California–Santa Cruz, Santa Cruz,
Nadine Quintana-Krupinski California 95064, USA
Chris D. Clark Department of Geography, University of Sheffield, Sheffield S10 2TN, UK
Charlotte Sjunneskog Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA
ABSTRACT
Subglacial lakes identified beneath the Antarctic Ice Sheet belong to a rare category of unexplored environments on Earth’s surface. The key to understanding the origin and longevity of
subglacial lakes is likely contained in their sedimentary sequences. Here we explore the nature
of a sedimentary succession in a deep tectonic trough identified as a prime candidate for a
large subglacial paleolake. The trough is the 100-km-long, 620-m-deep Christie Bay, located
in the east arm of the Great Slave Lake, Canada. High-resolution seismic reflection data and
short sediment cores collected in the deep trough show a 150-m-thick sequence of fine-grained
sedimentary lake fill separating glacial ice-contact deposits from draped Holocene lake sediments. We interpret this sequence to consist of sediments that accumulated in a subglacial lake
that covered an area larger than 130 km2. The inferred presence of a subglacial paleolake is
supported by results from hydrologic modeling of drainage pathways beneath the Laurentide
Ice Sheet during the last glacial maximum. Our data point toward the existence of a dynamic
subglacial lake environment where sediments were delivered by discharge of meltwater from
a subglacial water system. A core sample of the sedimentary lake fill in Christie Bay may elucidate whether living organisms exist in subglacial lakes.
Keywords: subglacial lake, ice sheet, sediment, hydrology, basal water.
INTRODUCTION
Recent observations show that dynamic subglacial water systems connect lakes beneath the
Antarctic Ice Sheet (Fricker et al., 2007; Gray
et al., 2005; Wingham et al., 2006). These water
systems may influence ice flow and deliver
energy sources as well as nutrients to microorganisms in subglacial lake environments
(Karl et al., 1999; Priscu et al., 1999). Comparable hydrologic systems may have existed
beneath the Laurentide Ice Sheet, which was
similar in size to the modern Antarctic Ice Sheet
and overrode numerous deep bedrock basins
suitable for development of subglacial lakes
(Evatt et al., 2006).
The Great Slave Lake in Canada is the deepest lake in North America and the sixth deepest
lake on Earth. The deepest part of Great Slave
Lake is the east arm, where the floor is 500 m
below modern sea level and 800 m below early
Holocene lake levels marked by raised beaches
(Smith, 1994). The morphology of a 100-kmlong, 620-m-deep trough in Christie Bay is
controlled by faults associated with a 2 Ga
transform structure (Hoffman, 1987). The geologic setting of Christie Bay is generally similar to that inferred for subglacial Lake Vostok,
Antarctica (Studinger et al., 2003). Recent
ice sheet reconstructions constrained by geodetic observations show that the ~4-km-thick
Keewatin Dome was centered over Great Slave
Lake during the last glacial maximum (LGM)
(Peltier, 2002) (Fig. 1).
To evaluate whether the bed of Keewatin Dome
was warm or cold, we solved the heat transfer equation for an ice divide (Paterson, 1994,
p. 220), using a geothermal heat flux of 55 mW
m–2 (Blackwell and Richards, 2004) and estimates of mean annual air temperature (−35 °C)
and precipitation (0.16 m yr –1) from LGM climate simulations (Bromwich et al., 2004). The
result indicates that wet basal conditions occurred
when ice thickness was >3 km. To estimate meltwater routing, we computed hydraulic potentials
using LGM ice-surface elevation (Peltier, 2002)
(Fig. 1A) and bed topography (Fig. 1B) derived
from a digital elevation model isostatically
adjusted proportional to ice thickness. These calculations suggest that meltwater from a subglacial
catchment covering ~30,000 km2 was routed to
Great Slave Lake and trapped in Christie Bay
(Fig. 1B). Using these quantitative estimates, we
developed the hypothesis that subglacial lakes
formed in Christie Bay during glaciations. To
test this hypothesis, we examined sedimentary
sequences in Christie Bay.
DATA ACQUISITION
During two geophysical cruises on Christie
Bay we acquired 500 km of seismic reflection
data and collected three 2-m-long sediment cores
from the lake floor. We used a 1-cubic-inch air
gun to examine the composition of the sedimentary sequences to bedrock, and a swept frequency
(2–16 kHz) sub-bottom profiler (CHIRP) to
acquire high-resolution images of the upper tens
of meters. To compute sediment thickness from
acoustic traveltimes we conservatively assumed
that speed of sound in saturated sediment was
1500 m s–1. The sedimentary sequence in Christie
Bay comprises four acoustic units. The deepest,
Unit 1, has a disconformable and hummocky
upper surface with strong but scattered acoustic
returns. The internal structure is massive and
dominated by hyperbolic diffractions. Unit 2 is
a seismically transparent body of concentrated
basin fill occurring below 470 m. The unit’s maximum thickness is at least 150 m. Unit 2 contains laterally continuous internal reflectors that
onlap Unit 1 and crystalline bedrock (Fig. 2A).
The geometry of these reflectors responds in
a muted fashion to underlying topographic
irregularities, which indicates considerable
consolidation and suggests that the sediment
is fine grained and compressible (Fig. 2B). A
gentle westward stratigraphic dip and a depositional center located 10 km east off the deepest
part of the basin indicate that sediment entered
the trough from the east (Fig. 2C). Unit 3 is a
laterally continuous and acoustically stratified sediment drape with thickness of 10–30 m
(Fig. 3). The sediment cores revealed that Unit
3 is laminated gray clayey silt (Fig. 4). Unit 4 is
also a laterally continuous sediment drape, but
unlike Unit 3, which it conformably overlies, it
is acoustically transparent and the thickness is
only up to a few meters (Fig. 3). The sediment
cores showed that this unit is finely laminated,
red-brown, silty clay (Fig. 4). Unit 4 is similar
to core samples recovered from McLeod Bay
(MB in Fig. 2C), where the Holocene sedimentation rate is ~0.06 mm yr –1 (Stoermer et al.,
1990). Such a low sedimentation rate is consistent with lack of major modern fluvial detrital
© 2008 The Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected].
GEOLOGY,
2008
Geology,
JulyJuly
2008;
v. 36; no. 7; p. 563–566; doi: 10.1130/G24628A.1; 4 figures.
563
0
70°N
0.0
A
0.1
150
20°W
0.2
Depth (m)
0.3
300
0.4
0.5
450
0.6
Bedrock
600
0.8
50°N
0.9
750
1.0
1.1
4
3
0.7
900 Multiples
2
1
0
1
Multiple
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Two-way traveltime (s)
100°W
70°N
A
180°W
1.2
16
120°W
100°W
80°W
B
110°W
B
4
3
65°N
2
Great Slave
Lake
Distance (km)
Distance (km)
30
C
0
50
150
100
20
150
300
MB
10
CB
GSL
0
1
450
0
10
20
30
40
50
600
60
70
Distance (km)
60°N
0
200
400 km
Figure 1. A: Last glacial maximum surface
elevation of Laurentide Ice Sheet based on
interpolated ICE5G model output (Peltier,
2002). Black box outlines area shown in B.
B: Subglacial meltwater routing beneath
Keewatin Dome. Black contours denote
hydraulic potentials. Thin blue lines mark
shorelines of modern lakes. Dark blue area
illustrates extent of subglacial catchment
where water flows to east arm of Great Slave
Lake. Light blue designates Christie Bay,
where trapped water forms subglacial lake.
inputs, as Christie Bay and McLeod Bay are
fed by small streams draining small, bedrockdominated watersheds that account for <2% of
the lake’s annual water balance (Gibson et al.,
2006). Low biogenic content and lack of diatom
shell fragments prevented us from dating Holocene sediments, but our sediment cores revealed
an abrupt change in grain size, lamina thickness,
color, magnetic susceptibility, and geochemical
composition between Units 3 and 4 (Fig. 4).
INTERPRETATION OF
SEDIMENTARY SEQUENCES
We interpret the hummocky Unit 1 to be
glacial moraine, the only ice-contact deposit
in the basin. Because the draped Units 3 and 4
correspond to characteristic late glacial and
postglacial sequences found in numerous lakes
564
315
Depth (m)
Lake
Athabasca
Figure 2. A: Seismic reflection data acquired with air gun showing acoustic properties
in transect across Christie Bay (CB). B: Close-up showing acoustic attributes of sedimentary units discussed in text. C: Bathymetry of CB derived from seismic data. Color
scale denotes water depths (m) and axes are in kilometers north and east from 62.4°N,
111.6°W. Black contours show thickness of sediment (m) interpreted to represent subglacial paleolake (Unit 2). Thick gray lines show location of seismic transects. Pink line
denotes transect shown in A and thin gray lines represent shorelines. Thick black line designates transect shown in Figure 3 and black dot indicates location of sediment core shown
in Figure 4. MB—McLeod Bay.
330
4
345
360
3
375
1
1.0
1.5
2.0
Distance (km)
2.5
Figure 3. Swept frequency (2–16 kHz) seismic reflection data showing Holocene sediments
draped over hummocky glacial moraine east of the deep trough. Numbers refer to sedimentary units.
on the Canadian shield (Shilts and Clague,
1992), we infer that Unit 2 was deposited
when a subglacial lake occupied Christie Bay.
Our data contain no evidence indicating that
Unit 2 consists of sediments from more than
one glaciation. If Unit 2 were to span multiple
glaciations, we would expect horizons of interglacial sediments similar to Units 3 and 4, or
if eroded, subglacial deposits similar to Unit 1,
or at least an erosional unconformity, but these
are not apparent. In our preferred interpretation,
the boundary between Units 3 and 4 marks the
cessation of input of glacially sourced detrital
material, as a result of eastward retreat of the
ice-sheet margin. The silt-rich sediment drape
containing Unit 3 represents late glacial lacustrine deposition by rainout during deglaciation
of Christie Bay, which started 9.9 14C ka B.P.
and the switch to deposition of clay-rich sediment (Unit 4) occurred 8.4 14C ka B.P., when
glacially derived waters no longer reached Great
Slave Lake (Lemmen et al., 1994; Smith, 1994)
and chemical subaerial weathering became the
predominant mode of debris generation.
The alternative to the above interpretation
is to consider the possibility that Unit 2 is part
of a massive late glacial lacustrine sequence.
However, collective deposition of Units 2 and 3
GEOLOGY, July 2008
Magnetic susceptibility
Grain size
0
A
Finely laminated,
silty clay, red-brown
C
B
0.2
P/Ti
D
E
Clay
Laminated, clayey
silt, gray
Depth below core top (m)
0.4
Silt
0.6
0.8
1.0
Sand
1.2
0
0.05
0.1
F
1.4
1.6
1.8
2.0
10 mm
0
50
100 10
%
20
30
SI
Figure 4. A: Optical images of core segments containing postglacial sediment (top) and late
glacial sediment (bottom). B: Grain size fractions. C: Magnetic susceptibility. D: Ratio of
phosphorous (P) over titanium (Ti) from X-ray fluorescence detection in Itrax core scanner.
E: X-ray radiograph of the upper 1.15 m of the sediment core. F: X-ray radiographs showing
internal structure of postglacial sediment (left) and late glacial sediment (right).
between 9.9 and 8.4 14C ka B.P. would require a
sedimentation rate more than an order of magnitude higher than what is observed in glacial
lakes along the southern rim of the Laurentide
Ice Sheet (Breckenridge et al., 2004; Dobson
et al., 1995). This explanation is not favored
because the southern ice-sheet margin was more
dynamic and considerably warmer and wetter than the Keewatin region (Bromwich et al.,
2005). Fast sedimentation, as inferred for a deep
lake in central British Columbia (Eyles et al.,
1990), is unlikely on the Canadian shield, where
easily erodible surface sediment is in short supply because Quaternary erosion occurred at
a rate of just 0.004 mm yr –1 (Hay, 1998). The
acoustic properties of Unit 2 and its internal
reflectors are consistent with lake fill deposited by hyperpycnal density flows (underflows)
(Mulder and Alexander, 2001), for example, as
found in Alpine mountain lakes affected by glaciation (van Rensbergen et al., 1999).
SEDIMENT AND
MELTWATER DYNAMICS
The depositional transition from underflows
to rainout corresponds to a sharp boundary
between Units 2 and 3 that we associate with
a change from subglacial to proglacial setting. Changes in the thermo-physical setting
of subglacial paleolake Christie at this transition may explain the change in predominant
depositional mechanism. We expect that the
GEOLOGY, July 2008
water column was convectively unstable in
subglacial paleolake Christie because the temperature of maximum density of fresh water
in a subglacial lake is lower than the freezing
temperature when the ice cover exceeds 3 km
(Wuest and Carmack, 2000). This means that
meltwater forming along the lake ceiling is
naturally denser than warmer ambient lake
water, and that meltwater-sediment mixtures
are likely to generate underflows. The magnitude of convective currents in Lake Vostok is
1 mm s–1 or less (Mayer et al., 2003; Wuest and
Carmack, 2000), which is two orders of magnitude smaller than currents near the bottom
of Lake Baikal (Wuest et al., 2005). We expect
that sedimentation by rainout was a result of
particles being suspended more easily and for
longer when deglaciation turned subglacial
paleolake Christie into a proglacial lake.
Because we could not date the sediment
cores, we used the North America deglaciation
chronology to derive linear sedimentation rates
(LSRs). The deposition of Unit 3 (16 km3) during 9.9–8.4 14C ka B.P. suggests that the LSR
was ~11 mm yr –1 when glacial runoff from the
Laurentide Ice Sheet entered Christie Bay. After
8.4 14C ka B.P., when the Laurentide Ice Sheet
runoff no longer reached Christie Bay, the LSR
dropped to ~0.2 mm yr –1. A comparable drop
in sedimentation rate was observed in recent
times when glacial meltwater ceased to enter a
lake near the Juneau Ice Field in Alaska (Gilbert
et al., 2006). Our estimates are also in good
quantitative agreement with those derived for
lakes along the southern Laurentide Ice Sheet
margin (Breckenridge et al., 2004; Dobson
et al., 1995). Unit 2 covers ~130 km2, but this
area is not a spatial restriction on the size of subglacial paleolake Christie. If the lake ceiling had
a tilt comparable to Lake Vostok, the lake could
have covered up to 400 km2.
So far, we cannot determine the longevity
of subglacial paleolake Christie, but the most
likely possibility is that it coincided with the
growth and decay of Keewatin Dome during
marine isotope stage 2 (25–10 14C ka B.P.).
This longevity estimate, ~15 k.y., is consistent
with the predicted duration of warm-based ice
over Great Slave Lake (Marshall and Clark,
2002), and it suggests that the subglacial LSR
was ~2 mm yr –1. To derive a minimum estimate, we used the modeled duration of warmbased ice beneath the Laurentide Ice Sheet as
a whole, ~25 k.y. (Tarasov and Peltier, 2007),
indicating that the LSR was >1 mm yr –1. None
of these sedimentation rates can be accounted
for by melt-out of debris from dirty basal ice,
which forms in finite layers where average
debris content tends to be <10% by mass and
vertical extent is <10 m (Alley et al., 1997). If
we assume that rates of ice flow and basal melting did not exceed 10 m yr –1 and 10 mm yr –1,
respectively, the basin-wide contribution to the
LSR from basal ice melting would be <0.1 mm
yr –1, as dirty basal ice would overlie only 10%
of the lake. A more abundant sediment source
is associated with meltwater flowing through
the subglacial catchment shown in Figure 1.
If the average suspended sediment concentration were ~10 g L–1, as measured in subglacial
water discharged at 10 m3 s–1 (Swift et al., 2005),
~2000 km3 of meltwater entered Christie Bay.
This is a rough but reasonable estimate, considering water fluxes of 5–50 m3 s–1 beneath the
Antarctic Ice Sheet (Fricker et al., 2007; Gray
et al., 2005; Wingham et al., 2006) and a required
basal melt rate of 2–4 mm yr –1, depending on
whether lake longevity was 15 or 25 k.y.
CONCLUSIONS
Our data contain no evidence of post-LGM
ice contact in the deep part of Christie Bay,
so we expect that there was a direct transition
from subglacial to proglacial lake. This transition is likely a result of subglacial lakes acting
as slippery spots that can prevent ice sheets
from grounding in deep water-filled depressions (Pattyn, 2004). The presence of laterally
continuous internal reflectors in the subglacial
lake sediment indicates that the characteristic
grain size of particles delivered to the lake floor
varied with time. The dense spacing of reflectors near the bottom of Unit 2 may be linked to
a transition from a high-energy to low-energy
565
environment as the lake formed. The stronger,
higher, and less densely spaced reflectors may
be associated with course-grained material
deposited when the inflow of water and sediments from subglacial conduits was high. When
the Laurentide Ice Sheet decayed, the lake
probably grew because the ice cover thinned
and subglacial meltwater became more abundant (Marshall and Clark, 2002). Based on the
extent of Unit 2, we estimate that ~50 km3 of
floodwater may have been routed to the Arctic
Ocean if the lake had a rapid demise.
Our data are inconsistent with the premise
that subglacial lakes are isolated and quiescent
systems, but they support observations from
Antarctica showing hydrologic activity and lake
interconnections. We expect that underflows
were a key supply mechanism of sediment, as
well as energy and nutrients, and that recurrent
hydrologic inputs from a basal water system
interfered with lake convection and limited the
residence time of water to a few hundred years.
A similar hydrologic setting exists in subglacial
Lake Ellsworth, West Antarctica, which is a candidate for future in situ exploration (Vaughan
et al., 2007). Sediment cores from modern subglacial lakes have not yet been sampled, but they
are expected to reveal how the lakes interact with
the overlying ice sheet. Subglacial paleolakes
may contribute with comparable information.
A sediment core from Christie Bay containing
Unit 2 may reveal how microbial organisms in
lakes adapt to glaciations.
ACKNOWLEDGMENTS
This project was supported by a grant to
Christoffersen from University Research Fund and a
grant to Tulaczyk from the National Science Foundation Office of Polar Programs. We thank David
Vaughan, Michael Studinger, and an anonymous person for helpful reviews.
REFERENCES CITED
Alley, R.B., Cuffey, K.M., Evenson, E.B., Strasser,
J.C., Lawson, D.E., and Larson, G.J., 1997,
How glaciers entrain and transport basal sediment: Physical constraints: Quaternary Science
Reviews, v. 16, p. 1017–1038.
Blackwell, D.D., and Richards, M.C., 2004, Geothermal map of North America: Tulsa, Oklahoma,
American Association of Petroleum Geologists, scale 1:6,500,000.
Breckenridge, A., Johnson, T.C., Beske-Diehl, S., and
Mothersill, J.S., 2004, The timing of regional
late glacial events and post-glacial sedimentation rates from Lake Superior: Quaternary Science Reviews, v. 23, p. 2355–2367.
Bromwich, D.H., Toracinta, E.R., Wei, H.L.,
Oglesby, R.J., Fastook, J.L., and Hughes, T.J.,
2004, Polar MM5 simulations of the winter climate of the Laurentide Ice Sheet at the LGM:
Journal of Climate, v. 17, p. 3415–3433.
Bromwich, D.H., Toracinta, E.R., Oglesby, R.J.,
Fastook, J.L., and Hughes, T.J., 2005, LGM
summer climate on the southern margin of the
566
Laurentide Ice Sheet: Wet or dry?: Journal of
Climate, v. 18, p. 3317–3338.
Dobson, D.M., Moore, T.C., and Rea, D.K., 1995,
The sedimentation history of Lake Huron and
Georgian Bay—Results from analysis of seismic-reflection profiles: Journal of Paleolimnology, v. 13, p. 231–249.
Evatt, G.W., Fowler, A.C., Clark, C.D., and Hulton,
N.R.J., 2006, Subglacial floods beneath ice
sheets: Royal Society of London Philosophical
Transactions, ser. A, v. 364, p. 1769–1794.
Eyles, N., Mullins, H.T., and Hine, A.C., 1990, Thick
and fast—Sedimentation in a Pleistocene fjord
lake of British Columbia, Canada: Geology,
v. 18, p. 1153–1157.
Fricker, H.A., Scambos, T., Bindschadler, R., and
Padman, L., 2007, An active subglacial water
system in West Antarctica mapped from space:
Science, v. 315, p. 1544–1548.
Gibson, J.J., Prowse, T.D., and Peters, D.L., 2006,
Hydroclimatic controls on water balance and
water level variability in Great Slave Lake:
Hydrological Processes, v. 20, p. 4155–4172.
Gilbert, R., Desloges, J.R., Lamoureux, S.F., Serink,
A., and Hodder, K.R., 2006, The geomorphic
and paleoenvironmental record in the sediments of Atlin Lake, northern British Columbia: Geomorphology, v. 79, p. 130–142.
Gray, L., Joughin, I., Tulaczyk, S., Spikes, V.B.,
Bindschadler, R., and Jezek, K., 2005, Evidence for subglacial water transport in the West
Antarctic Ice Sheet through three-dimensional
satellite radar interferometry: Geophysical
Research Letters, v. 32, L03501, doi: 10.1029/
2004GL021387.
Hay, W.W., 1998, Detrital sediment fluxes from continents to oceans: Chemical Geology, v. 145,
p. 287–323.
Hoffman, P.F., 1987, Continental transform tectonics—
Great Slave Lake shear zone (ca. 1.9 Ga), northwest Canada: Geology, v. 15, p. 785–788.
Karl, D.M., Bird, D.F., Bjorkman, K., Houlihan, T.,
Shackelford, R., and Tupas, L., 1999, Microorganisms in the accreted ice of Lake Vostok:
Antarctic Science, v. 286, p. 2144–2147.
Lemmen, D.S., Dukrodkin, A., and Bednarski, J.M.,
1994, Late glacial drainage systems along the
northwestern margin of the Laurentide Ice
Sheet: Quaternary Science Reviews, v. 13,
p. 805–828.
Marshall, S.J., and Clark, P.U., 2002, Basal temperature evolution of North American ice sheets
and implications for the 100-kyr cycle: Geophysical Research Letters, v. 29, 2214, doi:
10.1029/2002GL015192.
Mayer, C., Grosfeld, K., and Siegert, M.J.,
2003, Salinity impact on water flow and
lake ice in Lake Vostok, Antarctica: Geophysical Research Letters, v. 30, 1767, doi:
10.1029/2003GL017380.
Mulder, T., and Alexander, J., 2001, The physical
character of subaqueous sedimentary density
flows and their deposits: Sedimentology, v. 48,
p. 269–299.
Paterson, W.S.B., 1994, The physics of glaciers (third edition): Oxford, ButterworthHeinemann, 480 p.
Pattyn, F., 2004, Comment on the comment by M. J.
Siegert on “A numerical model for an alternative origin of Lake Vostok and its exobiological implications for Mars’’ by N. S. Duxbury et al.: Journal of Geophysical Research,
v. 109, E11004, doi: 10.1029/2004JE002329.
Peltier, W.R., 2002, Global glacial isostatic adjustment: Palaeogeodetic and space-geodetic tests
of the ICE-4G (VM2) model: Journal of Quaternary Science, v. 17, p. 491–510.
Priscu, J.C., Adams, E.E., Lyons, W.B., Voytek,
M.A., Mogk, D.W., Brown, R.L., McKay,
C.P., Takacs, C.D., Welch, K.A., Wolf, C.F.,
Kirshtein, J.D., and Avci, R., 1999, Geomicrobiology of subglacial ice above Lake Vostok:
Antarctic Science, v. 286, p. 2141–2144.
Shilts, W.W., and Clague, J.J., 1992, Documentation of earthquake-induced disturbance of lake
sediments using subbottom acoustic profiling:
Canadian Journal of Earth Sciences, v. 29,
p. 1018–1042.
Smith, D.G., 1994, Glacial Lake McConnell—
Paleogeography, age, duration, and associated
river deltas, Mackenzie River Basin, western
Canada: Quaternary Science Reviews, v. 13,
p. 829–843.
Stoermer, E.F., Schelske, C.L., and Wolin, J.A.,
1990, Siliceous microfossil succession in
the sediments of McLeod Bay, Great Slave
Lake, Northwest Territories: Canadian Journal of Fisheries and Aquatic Sciences, v. 47,
p. 1865–1874.
Studinger, M., Karner, G.D., Bell, R.E., Levin, V.,
Raymond, C.A., and Tikku, A.A., 2003, Geophysical models for the tectonic framework
of the Lake Vostok region, East Antarctica:
Earth and Planetary Science Letters, v. 216,
p. 663–677.
Swift, D.A., Nienow, P.W., and Hoey, T.B., 2005,
Basal sediment evacuation by subglacial meltwater: Suspended sediment transport from Haut
Glacier d’Arolla, Switzerland: Earth Surface
Processes and Landforms, v. 30, p. 867–883.
Tarasov, L., and Peltier, W.R., 2007, Coevolution
of continental ice cover and permafrost extent
over the last glacial-interglacial cycle in North
America: Journal of Geophysical Research,
v. 112, F02S08, doi: 10.1029/2006JF000661.
van Rensbergen, P., de Batist, M., Beck, C., and
Chapron, E., 1999, High-resolution seismic
stratigraphy of glacial to interglacial fill of a
deep glacigenic lake: Lake Le Bourget, Northwestern Alps, France: Sedimentary Geology,
v. 128, p. 99–129.
Vaughan, D.G., Rivera, A., Woodward, J., Corr,
H.F.J., Wendt, J., and Zamora, R., 2007,
Topographic and hydrological controls on
subglacial Lake Ellsworth, west Antarctica:
Geophysical Research Letters, v. 34, L18501,
doi: 10.1029/2007GL030769.
Wingham, D.J., Siegert, M.J., Shepherd, A., and
Muir, A.S., 2006, Rapid discharge connects
Antarctic subglacial lakes: Nature, v. 440,
p. 1033–1036.
Wuest, A., and Carmack, E., 2000, A priori estimates
of mixing and circulation in the hard-to-reach
water body of Lake Vostok: Ocean Modelling,
v. 2, p. 29–43.
Wuest, A., Ravens, T.M., Granin, N.G., Kocsis, O.,
Schurter, M., and Sturm, M., 2005, Cold intrusions in Lake Baikal: Direct observational evidence for deep-water renewal: Limnology and
Oceanography, v. 50, p. 184–196.
Manuscript received 1 December 2007
Revised manuscript received 17 March 2008
Manuscript accepted 22 March 2008
Printed in USA
GEOLOGY, July 2008