International Polar Year 2007–2008 - WMO

Fig. 2.6-3. Russian
scientific traverses in
the Lake Vostok area
(left) and subglacial
landscape of Lake
Vostok depression
as revealed by
RES and seismic
measurements (right),
courtesy of Sergey
Popov (PMGRE).
Shown on the map: 1-
radio-echo sounding
profiles; 2- reflection
seismic stations; 3-
VFL and NVFL ice-flow
lines (the studied
segments of the flow
lines are highlighted
with thicker curves);
4 – the expansions
of Lake Vostok water
table.
248
IPY 20 07–20 08
the northern part of Lake Vostok (Fig. 2.6-3). The age
and the location of lake accretion ice formation in the
Vostok core, as inferred from the ice flow modeling,
is illustrated in Fig. 2.6-4 (Salamatin et al., 2009). The
upper stratum of lake ice bedded between 3539 and
3609 m beneath the surface comprises scarce mineral
inclusions entrapped from the lake bottom sediments
in the shallow strait and/or over the small island on the
upstream side of Lake Vostok. The underlying clean ice
is assumed to be refrozen from the deep water as the
ice sheet moved between the “islet” and Vostok Station
(Fig. 2.6-4).
Extensive study of mineral inclusions conducted
at the Institute for Geology and Mineral Resources of
the World Ocean (VNIIOkeangeologia) and at the All-
Russian Geological Institute (VSEGEI) showed that in
most cases they were soft aggregates composed of
micro-particles of clay-mica minerals, quartz and a variety
of accessory minerals (see inset in Fig. 2.6-4). The
larger (up to 4-5 mm) rock clasts found in the inclusions
were classified as quartzose siltstone comprised
of zircon and monazite grains. The composition of the
clasts confirms that the bedrock to the west of Lake
Vostok (a potential source of terrigenous material in
the ice core) is of sedimentary origin. The ages of zircon
and monazite grains cluster between 0.8−1.2 Ga
and 1.6−1.8 Ga, which suggests that the provenances
of these sedimentary rocks, the Gamburtsev Moun-
tains and Vostok Subglacial Highlands, are mainly Paleoproterozoic
and Mesoproterozoic-Neoproterozoic
crustal provinces (Leitchenkov et al., 2007).
Resumption of deep drilling at Vostok Station
during IPY allowed an extension of the ice core isotopic
(d 18 O and dD) profile of accreted ice to 3650 m depth.
Analysis of the data set with the aid of an isotopic
model of Lake Vostok revealed significant spatial and/
or temporal variability in physical conditions during ice
formation as well as variability in the isotopic content
of freezing lake water (Ekaykin et al., 2010). The data
suggested that there was a significant contribution of
a hydrothermal source (2.8-5.5 mt of water per year)
to the hydrological regime of the lake. Independent
evidence (Jean-Baptiste et al., 2001; Bulat et al., 2004;
de Angelis et al., 2004) including recent data on the
distribution of helium isotopes (Jean-Baptiste, pers.
comm., 2009) supports this inference. The extent to
which Lake Vostok may be hydraulically connected
with other components of the hydrological system
beneath the Antarctic ice sheet cannot be assessed
from such isotopic data. Precise geodetic GPS
observations, from the southern part of Lake Vostok
throughout IPY, have demonstrated that, at least on
the time scale of five years, the lake and the ice sheet
in the vicinity of Vostok Station are in steady-state
(Richter et al., 2008) whereas other subglacial lakes
show highly dynamic behaviours.