Deep radiostratigraphy of the East Antarctic plateau: connecting
the Dome C and Vostok ice core sites
MARIE G. P. CAVITTE,1
DONALD D. BLANKENSHIP,1
DUNCAN A. YOUNG,1
DUSTIN M. SCHROEDER,2
* FRÉDÉRIC PARRENIN,3
EMMANUEL LEMEUR,3
JOSEPH A. MACGREGOR,1
† MARTIN J. SIEGERT4
1
Institute for Geophysics, University of Texas at Austin, Texas 78758, USA
2
Jet Propulsion Laboratory, California Institute of Technology, CA, USA
3
Laboratoire de Glaciologie et Géophysique de l’Environnement, CNRS, UJF-Grenoble I, BP 96, F-38402 Saint-Martin
d’Hères, France
4
Grantham Institute and Department of Earth Science and Engineering, Imperial College London, London SW7 2AZ, UK
Correspondence: Marie Cavitte <mcavitte@ig.utexas.edu>
ABSTRACT. Several airborne radar-sounding surveys are used to trace internal reflections around the
European Project for Ice Coring in Antarctica Dome C and Vostok ice core sites. Thirteen reflections,
spanning the last two glacial cycles, are traced within 200 km of Dome C, a promising region for
million-year-old ice, using the University of Texas Institute for Geophysics High-Capacity Radar
Sounder. This provides a dated stratigraphy to 2318 m depth at Dome C. Reflection age uncertainties
are calculated from the radar range precision and signal-to-noise ratio of the internal reflections. The
radar stratigraphy matches well with the Multichannel Coherent Radar Depth Sounder (MCoRDS)
radar stratigraphy obtained independently. We show that radar sounding enables the extension of ice
core ages through the ice sheet with an additional radar-related age uncertainty of ∼1/3–1/2 that of
the ice cores. Reflections are extended along the Byrd-Totten Glacier divide, using University of
Texas/Technical University of Denmark and MCoRDS surveys. However, core-to-core connection is
impeded by pervasive aeolian terranes, and Lake Vostok’s influence on reflection geometry. Poor
radar connection of the two ice cores is attributed to these effects and suboptimal survey design in
affected areas. We demonstrate that, while ice sheet internal radar reflections are generally isochronal
and can be mapped over large distances, careful survey planning is necessary to extend ice core chronologies
to distant regions of the East Antarctic ice sheet.
KEYWORDS: airborne electromagnetic soundings, ice chronology/dating, radio-echo sounding
1. INTRODUCTION
Ice cores retrieved from East Antarctica provide the longest
record of direct greenhouse gas concentrations and are
key to understanding late Quaternary climate forcings. The
European Project for Ice Coring in Antarctica (EPICA)
Dome C (EDC) (75°06′S, 123°21′E; Augustin and others,
2004) and Vostok (78°28′S, 106°52′E; Petit and others,
1999) ice cores provide dated records down to the depths
of 3193 and 3272 m, respectively, corresponding to ages of
808 and 407 ka, respectively (Bazin and others, 2013;
Veres and others, 2013). However, age uncertainties at
such depths become significant using traditional ice core
dating methods: single core chronologies vary between confidence
intervals of 2 ka at Vostok (O2/N2 dating method;
Suwa and Bender, 2008) and 6 ka at Dome C (EDC3 chronology;
Parrenin and others, 2007) for ice older than 100 ka.
Given these age uncertainties, there are limits on the temporal
and spatial synchronicity and duration of climate
change interpretations available from ice core chronologies.
To improve the chronologies, efforts have been focussed on
developing multi-core statistical approaches such as the
Antarctic Ice Core Chronology 2012 (AICC2012) timescale
(Lemieux-Dudon and others, 2010; Bazin and others, 2013;
Veres and others, 2013), which synchronizes five deep
polar ice cores. Both cores also lack a well established absolute
depth certainty (Parrenin and others, 2012). For any deep
ice core, factors such as borehole inclination, post-coring relaxation,
broken-core length errors, logging gauge uncertainties
and temperature of logging with respect to in-situ
temperature can induce several meters of accumulated
error (Parrenin and others, 2012). With the introduction of
radio-echo sounding (RES) recording isochronous layering
over hundreds of kilometers, the age/depth record represented
by ice cores can benefit substantially from extensive
site selection activity, giving additional local knowledge
about bed, surface and internal reflections before the core
is drilled and to inform flow modeling for developing ice
core chronologies. We adopt the AICC2012 chronology to
date the radar reflections in this study as that chronology
should provide the best comparison of ages between the
EDC and Vostok ice core.
In Antarctica, internal RES reflections are pervasive and
can be related to (1) density changes, (2) ice chemistry variation
and/or (3) ice fabrics (Clough, 1977; Fujita and Mae,
* Stanford University, CA, USA.
† Cryospheric Sciences Laboratory (Code 615), NASA Goddard
Space Flight Center, Greenbelt, Maryland 20771, USA.
Journal of Glaciology (2016), 62(232) 323–334 doi: 10.1017/jog.2016.11
© The Author(s) 2016. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.
org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
. https://doi.org/10.1017/jog.2016.11
Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:33:44, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms
1994; Fujita and others, 1999). For the depths considered in
this study, ice chemistry variation is thought to be the dominant
source of internal radar reflections. Chemistry variations
result from the deposition of discrete acidic aerosols as laterally
extensive sheets on the ice surface, preserved by
later accumulation (Millar, 1981, 1982; Fujita and Mae,
1994; Siegert and others, 1998a). The radar stratigraphy
represents an additional method for ice core chronology extrapolation
as it is related to discrete volcanic events and not
solely climatic events. The isochronous nature of internal
reflections has been discussed and exploited over the past
∼40 years; Whillans (1976) first showed their usefulness as
isochrones in ice sheet models, Fujita and others (1999)
pointed out the lateral continuity of the internal reflections
and therefore the validity of their use as isochronal
markers, Jacobel and others (1993) then demonstrated their
use as markers of internal flow properties.
Modern RES surveys of the ice sheet provide the potential
for extending ice core age/depth relationships over large
areas where no cores exist (e.g. Siegert and others, 1998b;
Huybrechts and others, 2009; Leysinger Vieli and others,
2011; MacGregor and others, 2015), and given good survey
coverage, for the connection of ice core chronologies
(Steinhage and others, 2013; MacGregor and others, 2015).
Internal reflectors have been increasingly used in the reconstruction
of temporal and spatial climate parameters (e.g.
Leysinger Vieli and others, 2011; MacGregor and others,
2015). Use of continuous radar stratigraphy as an alternative
method for ice core extrapolation has the advantage of (1)
imaging spatially large areas to map englacial flow and (2)
extending the stratigraphies measured in ice cores to other
places (Parrenin and others, 2012). Extensive RES stratigraphy
can provide the level of depth and age accuracy needed for
modeling studies and is proving extremely useful in the community’s
search for million-year-old ice (Fischer and others,
2013). Furthermore, through the collection of surveys that
use coherent radar combined with a gridded survey design,
RES stratigraphy could help constrain depth errors and
inform ice core synchronization methods (e.g. LemieuxDudon
and others, 2010; Bazin and others, 2013; Veres and
others, 2013). In this study, we attempt to connect the Dome
C and Vostok ice core sites and evaluate the challenges associated
with such extensions of ice core stratigraphy.
2. DATA AND METHODS
2.1. Radar surveys
We use RES lines acquired over several seasons by the
University of Texas Institute for Geophysics (UTIG) aerogeophysical
program (Fig. 1). The radar system operates with a
center frequency of 60 MHz (Blankenship and others,
2001). Pre-2008 radar data (University of Texas/Technical
University of Denmark (UT/TUD); Vostok site coverage)
were acquired using a pulse width of 290 ns (∼24.4 m in
ice) and a pulse repetition frequency (PRF) of 12.5 kHz; log
detected signals were digitised at 16 ns intervals for 65.5 s
and incoherently stacked 2048 times to generate a trace
every ∼20 m along-track (Carter and others, 2009). Post-
2008 data (High Capacity Airborne Radar Sounder
(HiCARS) 1&2, Dome C site coverage) were acquired using
a 1 µs chirp width with a 15 MHz bandwidth corresponding
to a 100 ns pulse after compression (∼8.4 m in ice) and a 6.4
kHz PRF; signals were digitised at 20 ns intervals and
coherently stacked ten times, log detected and incoherently
stacked five times to yield records every ∼22 m along-track
(Young and others, 2011). Unfocussed coherent stacking
improves the signal-to-noise ratio (SNR) of flat internal reflections
and reduces surface scattering but can eliminate
dipping reflectors, while incoherent stacking retains steeply
dipping reflections with some loss of geometric fidelity
(Peters and others, 2007). In parallel, we use an RES line
acquired by the Center for Remote Sensing of Ice Sheets,
University of Kansas (CReSIS) Multi-Channel Coherent
Radar Depth Sounder (MCoRDS) in 2013 (MCoRDS, v2;
Rodríguez-Morales and others, 2014). The radar system operates
with a 180–210 MHz frequency range with multiple
receivers and an adjustable bandwidth up to 30 MHz, corresponding
to a post-processing 4.5 m vertical resolution in ice
and a data product with an along-track sampling of 30 m
(Leuschen and others, 2000).
2.2. Internal reflection tracing strategy
Data interpretation is performed by tracking continuous radar
reflections in ice following peaks in processed amplitude using
Landmark’s Decision Space Desktop 5000.8.3.0. Reflections
are traced using a semi-automated tracking algorithm that
uses an adjustable travel-time window to track peaks in
echo amplitude. This tracing was completed in three phases:
Fig. 1. Map of the East Antarctic plateau focussed on the study area.
A red box locates the study area in East Antarctica in the inset. All the
radar transects used are shown in red (High-Capacity Radar Sounder
(HiCARS) coherent radar data), magenta (University of Texas/
Technical University of Denmark (UT/TUD) incoherent radar data)
and a blue (Multichannel Coherent Radar Depth Sounder
(MCoRDS) coherent radar data) overlaid on ice surface velocities
(Rignot and others, 2011). Dark gray contours are RADARSAT-1
Antarctic Mapping Project (RAMP) ice surface elevation (m) (Liu
and others, 2001) and purple outlines ice divides (Bamber and
others, 2009). Black highlights the extent of the transects displayed
in Figures 2, 4 and 5 and Figure S1 and letters A-A’, B-B’, C-C’
and D-D’ provide orientation; yellow squares locate the aeolian
features in Figure 7; blue triangles mark the locations of the two
deep ice core sites connected in this study; a yellow star locates
where radar reflections are initiated; Lake Vostok is outlined in
blue. The basemap uses the Scientific Committee on Antarctic
Research (SCAR) projection. (UT/TUD/Lake Vostok Survey (LVS)
from Carter and others (2007); International Collaborative
Exploration of the Cryosphere through Airborne Profiling/
International Polar Year (ICECAP/IPY) in Young and others (2011);
(Blankenship and others, 2012a, b)).
324 Cavitte and others: Deep radiostratigraphy of the East Antarctic plateau: connecting the Dome C and Vostok ice core sites
. https://doi.org/10.1017/jog.2016.11
Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:33:44, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms
(1) Dome C stratigraphy – First, we tested the accuracy of the
HiCARS radar system for radar stratigraphy by tracing
radar reflections beginning at the furthest point from the
Dome C ice core site (Fig. 1) and tracked them continuously
to the Dome C ice core site – a distance of ∼230 km –
where their travel-times were recorded. All HiCARS
radar transects were used in this exercise to ensure a
large number of crossovers (30), supporting the reliability
of reflection tracing. Our reflection selection criteria are
based on echo strength and continuity: reflections
chosen have to be distinguishably brighter than adjacent
layers and continuous, based on visual identification in
Decision Space Desktop. If one of these properties
failed, the reflection being traced was terminated.
Reflections were sampled throughout the entire ice
column at regular depth intervals, where possible.
(2) MCoRDS repeat – Second, we repeated the same steps
using a MCoRDS radar transect, starting at the same location
(at the intersection of the MCoRDS and the HiCARS
radar transects; Fig. 1). Reflections at similar depths to
those observed in HiCARS were traced to the Dome C
ice core site. The MCoRDS transect stopped short of
the Dome C ice core site, we therefore extended the
MCoRDS-traced reflections onto two short HiCARS segments
to measure their respective travel-times at the
same site for comparison.
(3) Bridge to Vostok – In the third and final phase, we
extended the HiCARS radar reflections described in the
first phase, but this time we extended them in the direction
of the Vostok ice core site along the UT/TUD
survey (Fig. 1), to connect the Dome C and the Vostok
ice cores. We independently repeated the same exercise,
using only the MCoRDS transect. The lack of crossovers
in both UT/TUD and MCoRDS data precluded circumventing
areas of disturbed internal stratigraphy.
Complex internal reflection geometries attributed to the
aeolian terranes and lake-induced strain-rate contrasts
required extensive manual interpretation of the reflections
(later section). Radar crossover errors (Supplement 1,
Fig. 2. Radargram of the EPICA Dome C ice core site, using the HiCARS radar system. Top panel shows the raw radargram, bottom panel
shows the radar reflections traced in blue. A vertical magenta line highlights the location of the ice core site; reflections are numbered
according to Table 1. Note the gentle uniform undulation of the radar reflections, ‘draping’ over the rougher bed topography. Horizontal
flow velocity is very low or negligible near the ice core site, and increases with radial distance from the dome.
325Cavitte and others: Deep radiostratigraphy of the East Antarctic plateau: connecting the Dome C and Vostok ice core sites
. https://doi.org/10.1017/jog.2016.11
Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:33:44, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms
Tables S1 and S2) give a qualitative measure of the reliability
of the internal stratigraphy and of the depth uncertainties
stated (described next).
2.3. Reflection depth estimation
A total of thirteen reflections are traced between the Dome C
and Vostok ice core sites. Some reflections can be traced
throughout the entire region, while others are restricted to
the Dome C area, which has a relatively conformable subhorizontal
internal stratigraphy (Fig. 2). The deepest reflection
traced at Dome C reaches 2318 m, which represents
73% of the full EDC core length retrieved. Reflection
depths relative to the surface are computed for each reflection
assuming a constant electromagnetic velocity of 168.5
and 300 m µs−1
in ice and air, respectively, obtained using
an ice dielectric constant ε′ of 3.17 (Gudmandsen, 1971;
Peters and others, 2005) and Cice ¼ Cair=
ffiffiffiffi
ε0
p
. Variations in
Cice are taken into account in calculating reflection depth uncertainties
(Fujita and others, 2000) (a detailed error analysis
is given below).
All thirteen reflections meet our reflection selection criteria
of brightness and continuity. Where a radar transect
intersects an ice core site, we measure reflection depths,
using diffraction hyperbolae in the radar data arising from
station structures as reference locations (e.g. Figs 2 and 5).
Depths are measured from the surface, to which we apply
firn corrections (zf) of 13.60 m and 14.60 m at Vostok and
Dome C, respectively. These corrections are computed
using Eqn (1) below, following Dowdeswell and Evans
(2004) and published vertical density profiles for each site
(Lipenkov and others, 1997; Barnes and others, 2002).
zf ¼
K
n0
i
Z
ðρi À ρðzÞÞ dz ð1Þ
where K is the coefficient adopted by Robin and others
(1969) (0.85 m3
Mg–1
), ni′ is the refractive index of solid ice
(1.78), ρi is the density of solid ice (0.917 Mg m–3
) and ρ(z)
is the density at a depth z (Mg m–3
).
These firn corrections are confirmed within uncertainty
bounds by a seismic refraction study at Dome C (12.52 ±
1.21 m; Gassett, 1982) and from literature at Vostok (15 ±
2 m; Dowdeswell and Evans, 2004).
2.4. Radar depth error sources
To assess the uncertainties in the dating of the radar reflections,
we first account for all known sources of error in determining
reflection depths. Errors arise from three sources: (1)
range estimate precision in determining reflection depth,
(2) firn correction and (3) variations in electromagnetic
wave (EM) propagation in ice. These are computed for
each radar system independently (UT/TUD, HiCARS and
MCoRDS) as their vertical resolution varies. Horizontal continuity
was assumed over the minor data gaps between the
ice core sites and the radar lines of closest approach, corresponding
to 1.2 and 0.4 km at Vostok and Dome C, respectively.
We describe treatment of each error in order:
(1) Vertical resolution of the radar system is given by the
measured field radar pulse width (Millar, 1982); it represents
24.4 m for the UT/TUD radar, 8.4 m for HiCARS
and 4.5 m for MCoRDS. However, the precision of
reflection depth estimates is a function of the radar
system’s pulse width and the SNR for each reflection at
each ice core site. This is given by the range precision
σ(r*), the standard deviation of the range estimate
(Appendix). Additional errors could arise from sub-resolution
reflector fluctuations, but the continuity of reflection
amplitudes and subsequent traceability of the
reflections suggests that this is not significant outside terranes
of disturbed radar reflections (aeolian terranes and
lake-induced strain rate contrasts).
(2) Firn correction uncertainty is given by published errors in
depth-density curves at each ice core site (see Section 2.3).
This represents a 2% standard error in density values at
EDC (Barnes and others, 2002) and we use the same
standard error at Vostok. This is propagated into the reflection
depth error and represents a variation of ±1.37 m
and ±1.35 m at Vostok and Dome C, respectively.
(3) The uncertainty arising from EM velocity in ice takes into
account variations of the dielectric constant due to
varying impurity concentrations, anisotropy and temperature
(Fujita and others, 2000; Dowdeswell and
Evans, 2004; Peters and others, 2005). EM velocities in
ice vary between 168 and 169.5 m µs−1
(Fujita and
others, 2000), which increases the uncertainty of our
depth measurements as we go further down the ice
column. This represents a maximum depth variation of
±11.69 and ±10.32 m at Vostok (UT/TUD) and Dome
C (HiCARS) for the deepest reflection traced, respectively,
and ±6.14 m at Vostok (MCoRDS, the deepest reflection
traced in this case is shallower than for the
other radar systems).
(4) All three sources of error are calculated at each ice core
site and for each radar system (Tables 1, 2 and 3).
In addition, a crossover error analysis is performed on all
cross-lines and reflections as an independent validation of
our reflection depth error estimates (Supplement 1). The measured
crossover errors are less than the depth error estimates,
further suggesting that our error estimates are conservative.
This is done for the Dome C district (Table S1), where reflections
are not perturbed by dune terranes (see Section 4), and
in the Vostok district (Table S2).
2.5. Reflection age attribution
Next, we date radar reflections at the Dome C and Vostok
sites using the published AICC2012 age/depth chronology
(Bazin and others, 2013; Veres and others, 2013) with the
caveat that ice core absolute depth errors have not been estimated
for the cores recovered at either site, but are thought to
‘sum up to several meters’ (Parrenin and others, 2012). We
linearly interpolate bagged ice core age/depth data to fit
our picked radar depths, and assign ages to the reflections.
Thirteen radar reflections spanning a ∼200 ka period,
from the last glacial to the MIS 8 glacial, are traced around
the EDC ice core site. Age coverage is shown in Figure 3.
Only three reflections out of thirteen could be connected to
the Vostok ice core site using MCoRDS (Fig. 4) due to the
complicating effects of aeolian terranes and Lake Vostok on
the radar reflections. More reflections are traced using the
UT/TUD data as a result of its coarser vertical resolution
(Fig. 5): reflections observed in the UT/TUD radar integrate
more physical reflectors than the higher bandwidth
326 Cavitte and others: Deep radiostratigraphy of the East Antarctic plateau: connecting the Dome C and Vostok ice core sites
. https://doi.org/10.1017/jog.2016.11
Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:33:44, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms
Fig. 3. Temporal coverage of the radar reflections used in this study. Red lines represent the AICC2012 ages for the thirteen radar reflections
traced. They are superimposed on the EDC δD record (Jouzel and others, 2007), which is based on the Parrenin and others (2007) EDC3
timescale. Gray vertical bars represent the reflection age uncertainty obtained. The radar reflections cover a period of time from Marine
Isotope Stage (MIS) 8 glacial up to the last glacial maximum.
Fig. 4. Radargram of the Vostok ice core site, using the MCoRDS radar system. Note the orientation of this transect is at an angle to that of
Figure 5. Top panel shows the raw radargram, bottom panel shows the radar reflections traced in blue. A vertical magenta line highlights the
location of the ice core site; reflections are numbered according to Table 3. Again, reflection geometries over Lake Vostok are complex and
strongly warped over the bed topography. The radar transect is mainly along-flow here, with ice flow going from C to C’ as indicated by the
dashed arrow.
327Cavitte and others: Deep radiostratigraphy of the East Antarctic plateau: connecting the Dome C and Vostok ice core sites
. https://doi.org/10.1017/jog.2016.11
Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:33:44, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms
Fig. 5. Radargram of the Vostok ice core site, using the UT/TUD radar system. Note the orientation of this transect is at an angle to that of
Figure 4. Top panel shows the raw radargram, bottom panel shows the radar reflections traced in blue. A vertical magenta line highlights
the location of the ice core site; reflections are numbered according to Table 1. Note this time the complex reflection geometries, as a
result of the steep bed topography and the presence of Lake Vostok. The radar transect is oblique to flow, as indicated by the arrow head.
Table 1. HiCARS radar reflections at Dome C
Reflection Depth Depth uncertainty Age Radar rel. age uncertainty Total age uncertainty* SNR
m ±m ka ±ka ±ka dB
1 699.59 2.67 38.10 0.23 0.62 8.60
2 797.07 2.93 46.29 0.27 0.76 7.95
3 1073.36 3.56 73.10 0.36 2.00 7.25
4 1169.68 3.15 81.83 0.26 1.55 19.40
5 1335.77 3.62 96.28 0.33 1.73 15.05
6 1444.06 3.90 105.98 0.40 1.79 14.60
7 1591.20 4.39 120.88 0.35 1.69 10.90
8 1679.99 4.54 127.64 0.35 1.78 12.50
9 1884.75 5.04 159.67 1.06 3.73 12.65
10 1911.97 5.14 165.13 1.12 3.35 11.55
11 2085.31 5.64 201.58 1.01 2.23 9.85
12 2190.95 5.92 219.56 1.16 2.82 9.30
13 2317.83 6.41 248.04 1.51 2.97 6.75
rel, relative.
Our top six reflections span the last glacial cycle; our bottom seven reflections span the penultimate glacial cycle.
* Note that here, total age uncertainty of an individual radar reflection represents the RMS of the Dome C relative radar age uncertainty of each radar reflection
and the ice core age uncertainty (AICC2012, (Bazin and others, 2013; Veres and others, 2013)).
328 Cavitte and others: Deep radiostratigraphy of the East Antarctic plateau: connecting the Dome C and Vostok ice core sites
. https://doi.org/10.1017/jog.2016.11
Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:33:44, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms
systems, so while more local discrete reflections are identifiable
in the more advanced data, reflections are more laterally
continuous in the older data. However, a few reflections
traced are unreliable (Fig. 6), also as a result of the presence
of aeolian terranes and Lake Vostok (later discussion).
Once dated, we then calculate age uncertainties for each
radar reflection. The total age uncertainty of an individual reflection
is a combination of the published ice core age uncertainty
(Bazin and others, 2013; Veres and others, 2013) and the
specific radar reflection’s depth error (described above). Each
radar reflection corresponds to a specific age gradient in the
age/depth ice core curve, due to variations in strain thinning
and accumulation rates through glacial/interglacial cycles.
This age gradient can be used to translate the reflection
depth error to a relative radar age error for each radar reflection.
The total age uncertainty for an individual radar reflection is the
RMS combination of the ice core published age error and the
relative radar age error for the individual radar reflection (different
for each radar system) (also used by MacGregor and others,
2015). All uncertainties are summarized in Tables 1–3.
3. RESULTS
A distinction must be made between the internal stratigraphy
within a ∼200 km radius of the Dome C ice core site, which
shows relatively uniform, sub-parallel and continuous reflections,
with that of areas further upflow towards Lake Vostok,
characterized by more complex or truncated reflections due
to the presence of the tectonically-controlled deep subglacial
Lake Vostok basin (Studinger and others, 2003), and aeolian
reworking of the ice surface. Figures 2, 4 and 5 show the contrast
in internal reflections between these two districts: the
Vostok transect shows strongly up- and down-warped reflections,
as they flow over the jagged bed topography, as
opposed to the ‘smooth’ Dome C stratigraphy. These various
transects have different orientations with respect to ice flow
and care must be taken when comparing them: Figure 2 is
mainly along the ridge, along-flow, with very low ice flow
speeds, while Figure 4 is mainly along-flow and Figure 5 is
oblique to flow, both with significantly higher flow speeds.
3.1. The Dome C district
The internal radar stratigraphy around Dome C is fairly
straightforward and conformable: all thirteen radar reflections
can be traced through the entire district, using all
radar lines available (Fig. 2). The surveys were designed as
grids, providing multiple intersecting lines and, therefore,
crossover points to ensure that the same radar reflection is
being tracked throughout (Supplement 1, Table S1). The
gridded parts of the survey provide a qualitative check on
the isochroneity of the radar reflections traced; spatially,
reflections intersect with themselves on radar cross-lines.
Table 1 shows the depth, age and uncertainty associated with
Table 2. MCoRDS radar reflections at Dome C
Reflection Depth Depth uncertainty Age Radar rel. age uncertainty. Total age uncertainty* SNR
m ±m ka ±ka ±ka dB
1 699.59 2.01 38.10 0.17 0.60 15.52
2 798.99 2.54 46.44 0.24 0.81 6.17
3 1073.36 2.98 73.10 0.30 1.99 10.01
4 1169.68 3.30 81.83 0.27 1.55 7.45
5 1335.77 3.65 96.28 0.33 1.73 8.54
6 1444.06 3.94 105.98 0.40 1.79 7.63
7 1591.20 4.20 120.88 0.34 1.69 13.49
8 1679.99 4.49 127.64 0.34 1.78 8.55
9 1884.75 5.02 159.67 1.06 3.73 7.97
10 1912.24 5.22 165.19 1.14 3.35 4.35
11 2085.31 5.51 201.58 0.99 2.22 8.30
12 2202.14 5.77 221.98 1.30 3.22 9.88
13 2317.83 6.06 248.04 1.43 2.93 10.39
rel, relative.
Our top six reflections span the last glacial cycle; our bottom seven reflections span the penultimate glacial.
* Note that here, total age uncertainty of an individual radar reflection represents the RMS of the Dome C relative radar age uncertainty of each radar reflection
and the ice core age uncertainty (AICC2012, (Bazin and others, 2013; Veres and others, 2013)).
Table 3. MCoRDS radar reflections at Vostok
Reflection Depth Depth uncertainty Age Radar rel. age uncertainty. Total age uncertainty* SNR
m ±m ka ±ka ±ka dB
1 568.38 1.80 37.95 0.15 1.22 11.55
3 1039.13 2.89 73.94 0.21 1.78 10.40
5 1380.45 3.68 97.61 0.28 1.70 13.55
rel, relative.
Only three reflections made it across to the Vostok ice core site, and we only report those three.
* Total age uncertainty of an individual radar reflection represents the RMS of the Vostok relative radar age uncertainty of each radar reflection and the ice core
age uncertainty (Bazin and others, 2013; Veres and others, 2013).
329Cavitte and others: Deep radiostratigraphy of the East Antarctic plateau: connecting the Dome C and Vostok ice core sites
. https://doi.org/10.1017/jog.2016.11
Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:33:44, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms
each reflection. The MCoRDS transect, as a separate radar
system, serves as an additional test of the accuracy of reflection
dating and assignment of errors. As it was collected at a different
bandwidth, center frequency and with different processing
steps, it is an ideal independent test of the accuracy of our
HiCARS internal reflections. Starting from the same site
(labeled in Fig. 1), we are able to match each HiCARS reflection
to a MCoRDS reflection. Table 2 shows reflection depths, ages
and uncertainties associated with the MCoRDS data.
3.2. Linking Dome C and Vostok
Radar internal stratigraphy becomes more complex as we
move upflow towards Lake Vostok (Figs 4 and 5). We
attempt to trace all thirteen reflections to the Vostok ice
core site. Again, this is done twice: once using mostly UT/
TUD incoherent radar data, and a second time with the independent
MCoRDS radar transect. Note the difference in character
of the reflections between the two radar systems (Figs 4
and 5), in part due to the difference in vertical exaggeration,
but also the orientation of the transect with respect to ice
flow. Using the MCoRDS data, only three reflections can
be traced continuously between Dome C and Vostok
(Fig. 4). The majority traced from Dome C stop short of the
Vostok region. Table 3 shows the depth, age and uncertainty
associated with the three connected reflections.
We are able to trace more reflections from Dome C all the
way to the Vostok site using the UT/TUD survey. Figure 5 displays
all eleven ‘successful’ radar reflections, where they
intersect the Vostok ice core site.
3.3. The Vostok district
We hypothesize that the lack of radar line crossovers precludes
the successful stratigraphic tie between the two ice
cores for all reflections. To test this, we attempt a short experiment
by tracing thirteen reflections inside the UT/TUD
Vostok grid, initiating them at the Vostok ice core site location
in the radargrams and expanding them as far out as possible
through the grid. Reflections are not chosen at random:
the ages obtained at Dome C for the thirteen reflections are
converted to an equivalent depth at Vostok using the
AICC2012 chronology. From the Dome C total age uncertainties
for each reflection, we calculate the depth uncertainty
range expected at Vostok, which gives us a depth
interval within which the brightest reflection is chosen, or
as close to it as possible. This is done to satisfy our reflection
selection criteria described earlier and choose reflections that
are of approximately the same age as at Dome C.
Fig. 6. Radar reflection age differences between Vostok and Dome
C ice cores using the combined HiCARS and UT/TUD radar systems,
as a function of their age at the Dome C ice core site using HiCARSdetermined
reflection ages. Each data point represents each of the
thirteen radar reflections traced. The vertical black dashed line
separates reflections belonging to the last glacial from the
penultimate glacial. Error bars are displayed for each reflection
representing the total age uncertainty for each system. Both age
uncertainties are displayed, red and blue corresponding to
HiCARS and UT/TUD, respectively. Three reflections fall well
outside their respective total age uncertainty bounds: we attribute
this to the presence of aeolian terranes in the vicinity of Lake Vostok.
Fig. 7. Radar transects showing aeolian terranes and features, for the
(a) MCoRDS, (b) HiCARS and (c) UT/TUD radar systems. Their
locations are highlighted on Figure 1. (a) Radar reflection (in blue)
truncated by an erosional surface on the MCoRDS transect. The
transect is oriented along-flow and ice thickness varies greatly
between ∼3050 and ∼4440 m. (b) A complete buried dune
structure displaying well distinguishable cross-strata separated
from the rest of the ice column by a highly visible upper and
lower erosional surface, highlighted by black arrows. The transect
is oriented along-flow and ice thickness is ∼3020 m. (c) Although
lower resolution, this incoherent transect shows a strong transition,
highlighted by arrows, between isochronal ‘well-behaved’ internal
reflections to more re-worked stratigraphy in the shallower
portion. The transect is oriented oblique to flow and ice thickness
is ∼3120 m.
330 Cavitte and others: Deep radiostratigraphy of the East Antarctic plateau: connecting the Dome C and Vostok ice core sites
. https://doi.org/10.1017/jog.2016.11
Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:33:44, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms
Although buried dune terranes are pervasive in the Vostok
grid (Fig. 7), the tight grid design enables circumvention of
highly disturbed areas. The multiple crossovers ensure that
the reflections traced are internally consistent and have the
isochronal character required. We then calculate crossover
errors for this set of reflections (Supplement 1, Table S2):
we show that they are below the radar depth uncertainty of
the UT/TUD system.
4. DISCUSSION
The straightforward internal reflections in the Dome C district
allow the retrieval of a reliable radar stratigraphy, where the
total age uncertainty for each reflection is dominated by ice
core age uncertainties and is only weakly impacted by the
additional relative uncertainties of the HiCARS system. Due
to the finer vertical resolution of MCoRDS, HiCARS reflections
can sometimes correspond to a set of several (thinner)
MCoRDS reflections (Supplement 2), in which case only
one of the sets is traced. However, as seen from Figure 8,
this does not affect the reflection matching. Figure 8 shows
the depth difference for a reflection traced with only
HiCARS versus only MCoRDS data, and the depth errors displayed
are the range precision errrors σ(r*), which are a function
of the radar vertical resolution and the SNR obtained for
each reflection. The repeatability of the radar stratigraphy
obtained from two independent radars supports our assumption
that our error estimates are conservative. This comparison
increases our confidence that the radar reflections
traced are isochronal, as the two radar systems not only
use different frequencies and processing steps, but are
flown over different parts of the ice surface. We note that
our third reflection selected at Dome C for its brightness is
dated at 73.10 ± 2.00 ka, and may originate from the
acidity peaks associated with the Toba event(s) (Svensson
and others, 2012).
Although the MCoRDS data have a finer vertical resolution
and use coherent processing, they are only a single
line, and, therefore, stratigraphically complex areas cannot
be avoided. The UT/TUD Vostok survey avoids this issue,
through its gridded survey design. The presence of buried
aeolian terranes can perturb reflection isochroneity, which
can be difficult to recognize in the absence of crossovers.
Figure 7a shows an example of such effects in the
MCoRDS data. This explains the difficulty in connecting
reflections between the Dome C and Vostok region.
However, for all three reflections continuously traced, the
age differences between the Dome C and Vostok sites fall
inside the total age uncertainty ranges (Fig. 9).
A majority of the thirteen reflections can be connected
from Dome C to the Vostok site as a result of the gridded
design of the UT/TUD survey. The difference in age for a reflection
between the two ice core sites varies within the total
age uncertainty ranges for most reflections, as seen from
Figure 6. However, this difference also varies beyond the
age uncertainties stated previously for a few reflections. We
suspect this is mostly due to the pervasive presence of
buried aeolian terranes, which affect all depths of the ice
column. These terranes are more difficult to recognize, due
to the incoherent processing and low bandwidth of the UT/
TUD data (Fig. 7c). In addition, the UT/TUD grid used to
trace the reflections around Vostok is connected to the
HiCARS lines via a single ∼200 km UT/TUD line (Fig. 1).
This means no crossovers can be used as checkpoints on
the integrity of the reflections used for 200 km, which we
Fig. 9. Radar reflection age differences between Vostok and Dome
C ice cores using the MCoRDS radar system, as a function of their
age at the Dome C ice core site using MCoRDS-determined
reflection ages. Each data point represents one of the thirteen
radar reflections traced. The vertical black dashed line separates
reflections belonging to the last glacial from the penultimate
glacial. Error bars are displayed for each reflection representing
the total age uncertainty for each system. Both age uncertainties
are displayed, red and blue corresponding to HiCARS and
MCoRDS, respectively. The age differences between the two cores
all fall within their total age uncertainty bounds. Only three
reflections could be traced between the two cores: we attribute
this to the pervasive presence of buried aeolian terranes, which
affect all depths of the ice column and preclude a successful
connection of the two cores.
Fig. 8. Radar reflection depth differences between HiCARS and
MCoRDS at Dome C using only σ(r*) depth errors, as a function of
their age at the Dome C ice core site using HiCARS-determined
reflection ages. Each data point represents one of the thirteen
radar reflections traced. The vertical black dashed line separates
reflections belonging to the last glacial from the penultimate
glacial. Error bars are displayed for each reflection representing
the depth uncertainty related to the SNR of the reflections only
(i.e. σ(r*) only), for each system. Both depth uncertainties are
displayed, red and blue corresponding to HiCARS and MCoRDS,
respectively. Reflection depths obtained are almost identical for
each independent radar system, except for one, and shows that
the depth uncertainty bounds are conservative.
331Cavitte and others: Deep radiostratigraphy of the East Antarctic plateau: connecting the Dome C and Vostok ice core sites
. https://doi.org/10.1017/jog.2016.11
Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:33:44, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms
conclude is the key to a successful radar connection of the
cores. We therefore infer that the total age uncertainty
bounds calculated for all radar reflections represent the
‘expected’ age uncertainty in the case of straightforward
and conformable stratigraphy. Our radar connection of the
two cores also agrees well in depth with that obtained
using volcanic tie-points in the cores (Parrenin and others,
2012) (see further details in Supplement 3).
Active dune terranes cover significant parts of the East
Antarctic plateau (Arcone and others, 2012a, b; Das and
others, 2013). Aeolian terranes are readily visible in the
HiCARS, UT/TUD and MCoRDS radar transects, as shown in
Figure 7; further internal details are identifiable in the coherent
radar profiles (HiCARS and MCoRDS). For UT/TUD data, the
type of processing applied and the coarser vertical resolution
of the radar system make identification of these dunes more difficult.
Aeolian terranes are therefore generally identified by the
presence of erosional surfaces in the UT/TUD data. These terranes
affect all depths of the ice column sampled by the reflections
traced, and their locations vary with depth. Note also that
significant reflection disruptions have been reported alongflow
lines over Lake Vostok: they are likely to be associated
with anomalously high accumulation over the lake edge
(Leonard and others, 2004). These can further compromise
the isochroneity of the internal reflections.
The crossover analysis performed for the Vostok districtreflections
gives us confidence that the incoherent UT/TUD
system is adequate for reflection tracing, despite its coarser
resolution. We therefore suggest that the link between the
Vostok and Dome C sites is limited by the suboptimal
survey design rather than perturbed reflections as a result of
buried aeolian terranes and lake-induced strain rate contrasts.
The lack of crossovers along the single ∼200 km
long UT/TUD line, and along the MCoRDS transect makes
it difficult to reliably extend radar reflections.
5. CONCLUSIONS
In this study, thirteen bright and continuous radar reflections
were identified in UTIG airborne surveys from 2000 to 2011
and traced around the EDC and Vostok ice core sites. These
tracings were repeated with the MCoRDS radar transect
flown between the two cores in 2013, and the respective
reflections show a good stratigraphic match. The reflection
ages span the last two glacial cycles, an important constraint
on ongoing modeling efforts in the area to identify millionyear-old
ice target sites (Fischer and others, 2013). We
show that in the vicinity of Dome C, radar reflections represent
very reliable isochronal surfaces, which will be key
to modeling efforts to select a new deep ice core site. As
we move away from Dome C and closer to Vostok, we
enter an area of buried aeolian terranes that rework and truncate
some radar reflections beyond isochroneity. Lake
Vostok also affects layer geometries as the ice flows over it,
due to anomalous accumulation effects and flow over steep
bedrock topography (Studinger and others, 2003; Leonard
and others, 2004), and can contribute to the complex stratigraphy
observed in the area. Despite these natural hurdles,
most reflections could be successfully traced along the
Byrd-Totten Glacier divide, connecting the two ice core sites.
It is still well within our reach to obtain a more complete and
direct chrono-stratigraphic link between the ice cores. It simply
requires the collection of further radar data with gridded survey
designs to get better alternative routes to link the Dome C and
Vostok areas. Our investigation informs us that the only impediment
to connecting the two cores more completely was
the design of these particular surveys, which was ultimately
not well suited to the particular challenges of the East
Antarctic plateau. However, we acknowledge that the
primary purpose of these surveys was not the connection of
the two cores. After tracing multiple reflections with a variety
of radar systems, processing techniques and survey geometries,
we advise survey designs that include numerous crossovers for
reliability and reproducibility of the reflection tracings, including
stratigraphically complex areas. Indeed, when it comes to
the latter, even the most recent radar systems and processing
techniques cannot recover a reflection that has been extensively
truncated or thickened/thinned. In those cases, we found that
the most reliable method was to circumvent the area, using
crossing transects. We therefore emphasize the importance
of collecting (pseudo-)grids over wide areas of Antarctica, as
well as carefully connecting interpreted radar surveys (and
new surveys) to existing ice cores. We encourage new linkages
with grid spacings appropriate for the regional distribution of
erosion-related unconformities. This spacing should be estimated
from the distribution of aeolian and strain rate anomalies
extracted from the existing surveys at the ice core districts,
needed for accurate ice core extrapolation objectives. On the
condition that further data can be collected, we are confident
that the two deep ice cores can be more fully connected,
thus providing additional information, and perhaps most usefully
depth uncertainties, in existing synchronizations.
SUPPLEMENTARY MATERIAL
To view supplementary material for this article, please visit
http://dx.doi.org/10.1017/jog.2016.11
ACKNOWLEDGEMENTS
This work was supported by NSF grants ANT-0733025 and
ARC-0941678, NASA grants NNX08AN68G, NNX09AR52G,
and NNX11AD33G (Operation Ice Bridge) to Texas, the
Jackson School of Geosciences, the G. Unger Vetlesen
Foundation, NERC grant NE/D003733/1 and the Global
Innovation Initiative award from the British Council. We acknowledge
the use of data products from CReSIS generated
with support from NSF grant ANT-0424589 and NASA
Operation IceBridge grant NNX13AD53A. A portion of this
work was carried out by the Jet Propulsion Laboratory,
California Institute of Technology under a contract with the
NASA. Operational support was provided by the U. S.
Antarctic Program and by the Institut Polaire Français PaulEmile
Victor (IPEV) and the Italian Antarctic Program (PNRA
and ENEA). We thank the staff of Concordia Station and the
Kenn Borek Air flight crew. Additional support was provided
by the French ANR Dome A project (ANR-07-BLAN-0125).
Finally, we thank the Scientific Editor and anonymous referees
for constructive reviews. We thank Justin Hiester for his editorial
help. This is UTIG contribution 2915.
REFERENCES
Arcone SA, Jacobel R and Hamilton G (2012a) Unconformable stratigraphy
in East Antarctica: part I. Large firn cosets, recrystallized
growth, and model evidence for intensified accumulation. J.
Glaciol., 58(208), 240–252
332 Cavitte and others: Deep radiostratigraphy of the East Antarctic plateau: connecting the Dome C and Vostok ice core sites
. https://doi.org/10.1017/jog.2016.11
Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:33:44, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms
Arcone SA, Jacobel R and Hamilton G (2012b) Unconformable stratigraphy
in East Antarctica: part II. Englacial cosets and recrystallized
layers. J. Glaciol., 58(208), 253–264
Augustin L and 9 others (2004) Eight glacial cycles from an Antarctic
ice core. Nature, 429(6992), 623–628
Bamber J, Gomez-Dans J and Griggs J (2009) A new 1 km digital elevation
model of the Antarctic derived from combined satellite
radar and laser data–Part 1: data and methods. Cryosphere,
3(1), 101–111
Barnes P 6 others (2002) Effect of density on electrical conductivity
of chemically laden polar ice. J. Geophys. Res., 107(B2), 2029
Bazin L and 9 others (2013) An optimized multi-proxy, multi-site
Antarctic ice and gas orbital chronology (aicc2012): 120–800
ka. Clim. Past, 9(4), 1715–1731
Blankenship DD, Morse DL, Finn CA, Bell RE, Peters ME, Kempf SD,
Hodge SM, Studinger M, Behrendt JC and Brozena JM (2001)
Geologic Controls on the Initiation of Rapid Basal Motion for
West Antarctic Ice Streams: A Geophysical Perspective Including
New Airborne Radar Sounding and Laser Altimetry Results, in
The West Antarctic Ice Sheet: Behavior and Environment (eds RB
Alley and RA Bindschadle), American Geophysical Union,
Washington, DC. doi: 10.1029/AR077p0105, 77.
Blankenship DD, Young DA and Kempf SD (2012a) IceBridge
HiCARS 1 L2 Geolocated Ice Thickness. Digital media, NASA
DAAC at the National Snow and Ice Data Center, Boulder,
Colorado, USA
Blankenship DD, Young DA and Kempf SD (2012b) IceBridge
HiCARS 2 L2 Geolocated Ice Thickness. Digital media, NASA
DAAC at the National Snow and Ice Data Center, Boulder,
Colorado, USA
Carter SP 5 others (2007) Radar-based subglacial lake classification
in Antarctica. Geochem. Geophys. Geosyst., 8(3)
Carter SP, Blankenship DD, Young DA and Holt JW (2009) Using
radar-sounding data to identify the distribution and sources of
subglacial water: application to Dome C, East Antarctica. J.
Glaciol., 55(194), 1025–1040
Clough JW (1977) Radio echo sounding: reflections from internal
layers in ice sheets. J. Glaciol, 18(78), 3–14
Das I 9 others (2013) Influence of persistent wind scour on the
surface mass balance of Antarctica. Nat. Geoscie., 6(5), 367–371
Dowdeswell J and Evans S (2004) Investigations of the form and flow
of ice sheets and glaciers using radio-echo sounding. Rep. Prog.
Phys., 67(10), 1821
Evans J and Hagfors T (1968) Radar astronomy. McGraw-Hill,
New York
Fischer H and 9 others (2013) Where to find 1.5 million year
old ice for the IPICS “Oldest Ice” ice core. Clim. Past, 9, 2489–
2505
Fujita S and Mae S (1994) Causes and nature of ice-sheet radio-echo
internal reflections estimated from the dielectric properties of ice.
Ann. Glaciol., 20(1), 80–86
Fujita S and 6 others (1999) Nature of radio echo layering in the
Antarctic Ice Sheet detected by a two-frequency experiment. J.
Geophys. Res.: Solid Earth (1978–2012), 104(B6), 13013–13024
Fujita S, Matsuoka T, Ishida T, Matsuoka K and Mae S (2000) A
summary of the complex dielectric permittivity of ice in the
megahertz range and its application for radar sounding of polar
ice sheets, in Physics of Ice Core Records, edited by T.
Hondoh, pp. 185–212, Hokkaido Univ. Press, Sapporo, Japan.
Gassett R (1982) Seismic refraction study at Dome C, Antarctica.
University of Wisconsin–Madison
Gogineni P (2012) CReSIS Radar Depth Sounder Data, Lawrence,
Kansas, USA. Digital Media. http://data.cresis.ku.edu/
Gudmandsen P (1971) Electromagnetic probing of ice, (ed. James R.
Wait). In Electromagnetic probing in geophysics, 1, 321, Golem
Press, Boulder, CO USA
Huybrechts P, Rybak O, Steinhage D and Pattyn F (2009) Past and
present accumulation rate reconstruction along the Dome
FujiKohnen radio-echo sounding profile, Dronning Maud Land,
East Antarctica. Ann. Glaciol., 50(51), 112–120
Jacobel RW, Gades AM, Gottschling DL, Hodge SM and Wright DL
(1993) Interpretation of radar-detected internal layer folding in
West Antarctic ice streams. J. Glaciol., 39, 528–537
Jouzel J and 9 others (2007) Orbital and millennial Antarctic climate
variability over the past 800,000 years. Science, 317(5839),
793–796
Lemieux-Dudon B and 8 others (2010) Consistent dating for
Antarctic and Greenland ice cores. Quat. Sci. Rev., 29(1),
8–20
Leonard K, Bell RE, Studinger M and Tremblay B (2004) Anomalous
accumulation rates in the Vostok ice-core resulting from ice flow
over Lake Vostok. Geophys. Res. Lett., 31(24)
Leuschen C, Gogineni S and Tammana D (2000) SAR processing of
radar echo sounder data. In Geoscience and Remote Sensing
Symposium, 2000. Proceedings. IGARSS 2000. IEEE 2000
International, volume 6, 2570–2572, IEEE
Leysinger Vieli GJ, Hindmarsh RC, Siegert MJ and Bo S (2011) Timedependence
of the spatial pattern of accumulation rate in East
Antarctica deduced from isochronic radar layers using a 3-D
numerical ice flow model. J. Geophys. Res.: Earth Surface
(2003–2012), 116(F2)
Lipenkov VY, Salamatin IAN and Duval P (1997) Bubbly-ice densification
in ice sheets: 11. Applications. J. Glaciol., 43(145)
Liu H, Jezek K, Li B and Zhao Z (2001) RADARSAT Antarctic
Mapping Project digital elevation model. National Snow and
Ice Data Center, Digital Media, National Snow and Ice Data
Centre, Boulder, CO, USA
MacGregor JA and 9 others (2015) Radiostratigraphy and age structure
of the Greenland Ice Sheet. J. Geophys. Res.: Earth Surf., 120
(2), 212–241
Millar D (1981) Radio-echo layering in polar ice sheets and past volcanic
activity. Nature, 292, 441–443
Millar D (1982) Acidity levels in ice sheets from radio echosounding.
Ann. Glaciol, 3, 199–203
Parrenin F and 9 others (2007) The EDC3 chronology for the EPICA
Dome C ice core. Clim. Past, 3(3), 485–497
Parrenin F and 9 others (2012) Volcanic synchronisation between
the EPICA Dome C and Vostok ice cores (Antarctica) 0–145 kyr
BP. Clim. Past, 8(3), 1031–1045
Peters ME, Blankenship DD and Morse DL (2005) Analysis techniques
for coherent airborne radar sounding: application to West
Antarctic ice streams. J. Geophys. Res.: Solid Earth (1978–
2012), 110(B6)
Peters ME and 5 others (2007) Along-track focusing of airborne radar
sounding data from west Antarctica for improving basal reflection
analysis and layer detection. IEEE Trans. Geosci. Remote
Sens., 45(9), 2725–2736
Petit JR and 9 others (1999) Climate and atmospheric history of the
past 420,000 years from the Vostok ice core, Antarctica.
Nature, 399(6735), 429–436
Rignot E, Mouginot J and Scheuchl B (2011) Ice flow of the Antarctic
ice sheet. Science, 333(6048), 1427–1430
Robin GdQ, Evans S and Bailey JT (1969) Interpretation of radio
echo sounding in polar ice sheets. Phil. Trans. R. Soc.
London. S. A, Math. Phys. Sci., 265 437–505
Rodríguez-Morales F and 9 others (2014) Advanced multifrequency
radar instrumentation for polar research. IEEE Trans Geosci.
Remote Sens., 52(5), 2824–2842
Siegert MJ, Hodgins R and Dowdeswell JA (1998a) Internal radioecho
layering at Vostok station, Antarctica, as an independent
stratigraphic control on the ice-core record. Ann. Glaciol., 27,
360–364
Siegert MJ, Hodgkins R and Dowdeswell JA (1998b) A chronology
for the Dome C deep ice-core site through radio echo layer correlation
with the Vostok Ice Core, Antarctica. Geophys. Res.
Lett., 25(7), 1019–1022
Steinhage D, Kipfstuhl S, Nixdorf U and Miller H (2013) Internal
structure of the ice sheet between Kohnen station and Dome
Fuji, Antarctica, revealed by airborne radio-echo sounding.
Ann. Glaciol., 54(64), 163–167
333Cavitte and others: Deep radiostratigraphy of the East Antarctic plateau: connecting the Dome C and Vostok ice core sites
. https://doi.org/10.1017/jog.2016.11
Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:33:44, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms
Studinger M and 9 others (2003) Ice cover, landscape setting, and
geological framework of lake vostok, East Antarctica. Earth
Planet. Sci. Lett., 205(3), 195–210
Suwa M and Bender ML (2008) Chronology 468 of the Vostok ice
core constrained by O2/N2 ratios of occluded air, and its implication
for the Vostok climate records. Quat. Sci. Rev., 27(11),
1093–1106
Svensson A and 9 others (2012) Direct linking of Greenland and
Antarctic ice cores at the Toba eruption (74 kyr BP). Clim. Past
Discussions, 8(6), 5389–5427
Veres D and 9 others (2013) The Antarctic ice core chronology
(aicc2012): an optimized multi-parameter and multi-site dating approach
for the last 120 thousand years. Clim. Past, 9(4), 1733–1748
Wehner DR (1995) High resolution radar. Norwood, MA, Artech
House, Inc
Whillans IM (1976) Radio-echo layers and the recent stability of the
West Antarctic ice sheet. Nature, 264, 152–155
Young DA and 9 others (2011) A dynamic early East Antarctic Ice
Sheet suggested by ice-covered fjord landscapes. Nature, 474
(7349), 72–75
APPENDIX
RADAR HORIZON RANGE PRECISION
Radio echo tracking of reflecting horizons
In this work, we use airborne RES data to trace continuous
reflectors between the Vostok and EDC ice cores. We
follow a well established approach in the glaciological interpretation
of ice penetrating radar stratigraphy by assuming
that continuous reflectors represent isochronous englacial
horizons (Siegert and others, 1998a; Dowdeswell and
Evans, 2004). By exploiting its capability to both track and estimate
the range to englacial reflecting horizons, RES data
offers the potential to compare and calibrate the time scale
records of distinct ice cores. The two primary factors that
govern the applicability and precision of this method of ice
core inter-comparison are (1) the continuous interpretability
of englacial reflectors (discussed in the text of this paper)
and (2) the precision of range estimates to those interpreted
reflectors (the subject of this Appendix).
Precision of range estimates to englacial reflectors
The precision of range estimates for point non-fluctuating
targets like the shallowly sloping englacial reflecting horizons
examined in this work are a function of the waveform
bandwidth, β, the horizon signal power, PL, the noise
power, N0, and the speed of light in ice, Cice, (Evans and
Hagfors, 1968). For this type of target, the variance of the
delay estimate, τ*, is given by
VarðτÃ
Þ ¼
N0
PL
1
β2
ðA1Þ
and the variance of the corresponding range estimate is
therefore
VarðrÃ
Þ ¼
Cice
2
 2
N0
PL
1
β2
ðA2Þ
where r* is the range estimate (Wehner, 1995). The SNR, of
the radar return from a reflecting horizon is
SNR ¼
PL
N0
ðA3Þ
and the range resolution of an ice penetrating radar system is
Δr ¼
Cice
2β
ðA4Þ
where Δr is the range resolution (Evans and Hagfors, 1968;
Wehner, 1995). By combining Eqns (A2)–(A4), the variance
in the range estimate for a horizon can be written in terms
of only the range resolution of the radar system and the
SNR of the radar reflection from that horizon:
VarðrÃ
Þ ¼
Δr2
SNR
: ðA5Þ
Therefore, the precision of a range estimate for a reflecting
englacial horizon at the 68% confidence level will be
given by
σðrÃ
Þ ¼
Δr
ffiffiffiffiffiffiffiffiffi
SNR
p ðA6Þ
where σ(r*) is the standard deviation of the range estimate. It
is worth noting (and apparent in Eqn (A6)) that the precision
of the range estimate to englacial reflector is better than the
range resolution of the ice penetrating radar for SNRs
greater than two. Indeed, as mentioned in Evans and
Hagfors (1968), “were it not for the noise, the finite signal
duration or bandwidth would not prevent the location of
the peak [of the reflecting horizon in range] to arbitrarily
high precision”.
Precision of range estimates for englacial reflectors in
this work
In this work, we use three ice penetrating radar systems: the
UT/TUD incoherent radar system with a 290 ns pulse and
corresponding in-ice range resolution of Δr = 24.4 m for
pre-2008 surveys (Carter and others, 2007), the HiCARS coherent
15 MHz bandwidth system with a pulse-compressed
in-ice range resolution of Δr = 8.4 m (Young and others,
2011) and the MCoRDS coherent 30 MHz bandwidth
system with a post-processing range resolution of Δr = 4.5 m
(Gogineni, 2012) for Cice = 168.5 m µs−1
. In our study areas,
the SNR of horizon echoes ranged from SNR = 1.12–11.82
dB for the UT/TUD system, from SNR = 6.75–19.40 dB for
the HiCARS system and from SNR = 4.35–15.52 dB for the
MCoRDS system. Using Eqn (A6), we find that the precision
of the range estimates in this study range from σ(r*) = 6.27–
21.48 m for the UT/TUD data used at the Vostok core, from
σ(r*) = 0.90–3.87 m for the HiCARS data used at the EDC
core and from σ(r*) = 0.75–2.73 m and σ(r*) = 0.95–1.36 m
for the MCoRDS data used for EDC and Vostok ice core
sites, respectively.
MS received 16 October 2015 and accepted in revised form 9 December 2015; first published online 28 March 2016
334 Cavitte and others: Deep radiostratigraphy of the East Antarctic plateau: connecting the Dome C and Vostok ice core sites
. https://doi.org/10.1017/jog.2016.11
Downloaded from https:/www.cambridge.org/core. University of South Bohemia, on 15 Feb 2017 at 13:33:44, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms