GRAPHIC: V. ALTOUNIAN/SCIENCESCIENCE science.orgBy Winnie ChuH
idden below the surface of the
Antarctic Ice Sheet, there is a vast
mass of liquid water generated by the
heating of Earth and frictional melt-
ing. Glaciologists have speculated
about the existence of a deep ground-
water system because of fast-flowing ice
streams in sedimentary basins that are likely
permeable. However, direct evidence of a
groundwater reservoir beneath the Antarctic
subglacial hydrologic system has
been elusive. On page 640 of this
issue, Gustafson et al. ( 1 ) pres-
ent geophysical observations of
saline groundwater saturating
a sedimentary basin beneath
the Whillans Ice Stream in West
Antarctica. This reservoir, lo-
cated near the subglacial Lake
Whillans, is estimated to con-
tain a water volume more than
10 times greater than that in the
overlaying subglacial hydrologic
system. This finding highlights
groundwater hydrology as a po-
tentially critical piece in under-
standing the effect of water flow
on Antarctic ice sheet dynamics.
Subglacial water moves along
the base of the Antarctic Ice
Sheet through an under-ice
plumbing network known as the
“subglacial hydrologic system”
( 2 – 5 ), which has so far been
considered to be a shallow or
interfacial system in which wa-
ter exists either at or very near
the base of the ice sheet. This
“shallow” subglacial hydrologic
system typically includes lakes
( 6 – 9 ), channels ( 2 , 3 ), linked
cavities ( 4 , 5 ), and porous sediments ( 8 , 10 ).
Water flow in the subglacial hydrologic
system plays an important role in modulat-
ing ice motion. In principle, ice motion is
sustained by sliding over the ice sheet bed
in a process known as basal sliding, which
deforms the shape of the ice during the pro-
cess. Subglacial water can affect the motion
by providing lubrication between the icesheet and the bedrock, leading to so-called
“hard-bed” sliding ( 3 , 5 ). Alternatively, water
flow can also influence ice motion by causing
the deformation of wet sediments beneath
ice streams or glaciers, leading to “soft-bed”
sliding ( 10 ). Through these two mechanisms,
water at the base of the ice sheet controls
Antarctica’s ice sheet dynamics and, poten-
tially, its contribution to sea level rise.
Many ice streams in Antarctica reside in
deep marine sedimentary basins, where both
of the aforementioned sliding processes oc-cur. The Whillans Ice Stream, which is located
in the Siple Coast region of West Antarctica
and is the focus of Gustafson et al., is a re-
gion where the ice rests on top of more than a
meter of permeable sediments. The Whillans
Ice Stream has a highly active subglacial
hydrological system. It contains subglacial
Lake Whillans, which episodically floods and
releases water into the Ross Sea ( 6 ). What is
particularly intriguing about Lake Whillans
is that unlike other Antarctic subglacial lakes,
it is unusually shallow—only about 6 m deep
at its driest ( 7 ). One reason for this could bebecause Lake Whillans is surrounded by per-
meable subglacial sediments ( 8 ). Subglacial
lake water, therefore, could be leaking into
a deeper bedrock in addition to being trans-
ported laterally at the ice bed by a subglacial
hydrologic system, resulting in a shallower
lake volume. However, radar-sounding ( 9 )
and seismic ( 7 ) observations could not con-
firm the existence of a deep groundwater
reservoir because of limitations in frequency,
bandwidth, and depth resolution.
Gustafson et al. present magnetotellu-
ric (MT) data—observations of
Earth’s natural magnetic and
electric field variation—and
other seismic evidence for a
groundwater reservoir be-
neath Lake Whillans (see the
figure). Their observation also
extends 100 km further down
the Whillans Ice Stream, where
it transitions from grounded
ice to a freely floating ice shelf.
MT is a passive electromagnetic
(EM) technique that can mea-
sure deep subsurface electrical
resistivity distribution on depth
scales ranging from tens of me-
ters to hundreds of kilometers.
Although commonly used to
identify terrestrial groundwater
( 11 ) and magmatic reservoirs
( 12 ), only a few studies have used
EM methods to investigate ice
sheet hydrology ( 13 ).
By using a combination of
MT and passive seismic receiver
function analysis, Gustafson et
al. discovered the existence of a
groundwater body inside a sedi-
mentary basin between 0.6 and
1.3 km thick. Subsequent data
analysis indicates that the water
in the reservoir is relatively fresh at the top,
where the groundwater is in contact with
the subglacial water system, but becomes
increasingly brackish with depth. The down-
glacier groundwater system at the Whillans
grounding zone also has seawater at shal-
lower depths compared with the groundwa-
ter reservoir beneath Lake Whillans.
Gustafson et al. offer a hypothesis to ex-
plain the upward freshening of the ground-
water reservoir. They propose that the saline
nature of the groundwater could be a re-
sult of seawater trapped during the mid-to-HYDROLOGYGroundwater under Antarctica goes deep
A vast fossil seawater reservoir has been found beneath the West Antarctic Ice Sheet
School of Earth and Atmospheric Sciences, Georgia
Institute of Technology, Atlanta, GA 30332 , USA. Email:
[email protected]Traditional view
Previous considerations
only included relatively
shallow hydrologic
components near the
glacial surface,
including subglacial
channels, sediment
canals, and distributed
drainage networks
(shown as orange
arrows).Updated view
An updated view should
include the deeper
groundwater reservoir
that sits in a permeable
sedimentary basin. The
reservoir may exchange
water with the
shallower hydrologic
components and affect
their behaviors.Thin tillImpermeable
basementPermeable
sedimentary basinSubglacial channels
or canalsThin tillImpermeableSubglacial c nels
or canalsUnderneath the Ross Ice Shelf
Gustafson et al. identified a saline groundwater system near Lake Whillans that
contains more water than the subglacial drainage and subglacial lake above it.6 MAY 2022 • VOL 376 ISSUE 6593 5770506Perspectives_15506687.indd 577 5/3/22 6:22 PM