Ice sheets and deep ice cores have yielded a wealth of paleoclimate information based on continuous dating methods while independent radiometric ages of ice have remained elusive. Here we demonstrate the application of (234U/238U) measurements to dating the EPICA Dome C ice core based on the accumulation of 234U in the ice matrix from recoil during 238U decay out of dust bound within the ice. Measured (234U/238U) activity ratios within the ice generally increase with depth while the surface areas of the dust grains are relatively constant. Using a newly designed device for measuring surface area for small samples, we were able to estimate reliably the recoil efficiency of nuclides from dust to ice. The resulting calculated radiometric ages range between 80 ka and 870 ka. Measured samples in the upper 3100 m fall on the previously published age-depth profile. Samples in the 3200–3255 m section show a marked change from 723–870 ka to 85 ka indicating homogenization of the deep ice prior to resetting of the (234U/238U) age in the basal layers. The mechanism for homogenization is likely enhanced lateral ice flow due to high basal melting and geothermal heat flux

Aciego, S.

Baur, H.

Bourdon, B.

Forieri, A.

Schwander, J.

Earth-prints Repository

Appendix:
Toward a Radiometric Ice Clock: Uranium Ages of the Dome C
Ice Core
Sarah M. Aciegoa,b,∗, Bernard Bourdona,c, Jakob Schwanderd, Heinrich Baura,
Alessandro Forierie
aInstitute of Geochemistry and Petrology, ETH Zurich, Switzerland.
bnow at Department of Geological Sciences, University of Michigan, Ann Arbor, MI
cnow at Ecole Normale Suprieure de Lyon, CNRS, Lyon, France
dClimate and Environmental Physics, Physics Institute, University of Bern, Switzerland.
eIstituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, Roma, Italy.
A.1. 234U Recoil-Accumulation Age Equation1
U-series ages determined from recoil products from dust into ice are determined based2
on the following age equations:3
234Uice, no initial component, from Fireman (1986)4
λ234U
ice
234 = fλ238U238dust
(
1− e−λ234t) (1a)
t =
(
− 1
λ234
)
ln
[
1−
(
λ234U234
λ238U238
)(
1
f
)]
(1b)
5
This assumes that the amount of uranium present in the initial precipitation (snow) is6
so small as to be negligible. This equation is similar to the equation for uranium-recoil7
comminution ages for small grains (Lee et al., 2010). An activity equation that takes into8
account initial U is as follows.9
∗Corresponding author; aciego@umich.edu
Preprint submitted to Quaternary Science Reviews April 5, 2011
234Uice, initial component10
The activity of 234U in the ice is due to (1) the recoil out of the dust plus (2) the
decaying initial 234U dissolved in the precipitation plus (3) the accumulation from the
decay of 238U dissolved in the precipitation. Part (1) is just Equation 1a, above, and
parts (2) and (3) are daughter-decay and daughter-accumulation equations that are readily
available in isotope geochemistry textbooks such as Faure and Mensing (2004) or Dickin
(2005). The resulting equation that combines (1), (2) and (3) is:
λ234U
ice
234 = fλ238U
dust
238
(
1− e−λ234t) + λ234U in234 e−λ234t + λ238U ice238 (1− e−λ234t) (2)
Rearranging and solving for t results in the recoil age:
t = −
(
1
λ234
)
ln
(
[U234]ice − f [U238]dust − [U238]ice
[U234]
in
ice − f [U238]dust − [U238]ice
)
(3)
2
A.2. Calculation of Density11
The average density of the mineral dust was calculated based on literature modal12
mineralogies for Dome C (Table A1) from Gaudichet et al. (1986, 1988). Gaudichet et al.13
(1988) indicated that metallic oxides found in at least one Vostok sample originated from14
contamination. Given that the high density and non-aerodynamic shape of metallic ox-15
ides make their transport to the high plateau unlikely, we do not include these in the16
calculation. Average densities, using pure mineral density values for identified minerals17
(Table A1), range between 2.6 and 2.62 g/cm3. More recently, Sala et al. (2008) also18
found talc and muscovite within Dome C ice. And, while no literature has presented19
direct evidence for carbonate in the Dome C ice, it is likely that previous procedures that20
melted ice without buffering the meltwater to neutral pH dissolved any carbonate. These21
three minerals, talc, muscovite, and carbonate, were incorporated into the density calcu-22
lation by assigning the Unidentified modal percentages to these higher density minerals23
and result in an average density of 2.64 ± 0.052 (2 S.D.).24
25
3
Table A1: Compiled Mineralogical Data
Vostok* Dome C*
Sample No. 1 2 3 4 5 1 2 3 4 5
Depth(m) 125 475 925 1675 2025 246 552 580 678 838
Age (ka) 5 24 60 122 150 6 16 18 36 50
density g/cm3 Relative abundances %
Illite 2.6a 30 19 33 24 24 34 28 26 32 34
Kaolinite 2.61a - - - - - 4 3 - - -
Chlorite 2.8b - 6 5 - 4 - 3 4 5 6
Smectite 2.6a 7 3 13 5 6 - - 6 - -
Quartz 2.65a 14 15 7 8 8 - 23 12 13 8
Feldspars 2.58a,c 6 17 18 10 18 12 23 22 13 18
Pyroxenes, Amphiboles 3.1a,d - - - - - 15 6 - 5 2
Amorph Si (opal) 2.07a 6 2 2 8 3 - 6 4 - -
Metallic Oxides 3.5-4.5 12 3 1 11 1 4 - - - -
Volcanic glass 2.38e - - - - - 11 - 6 5 -
Colloidal 12 7 - 14 6 - - - - -
Ca Compounds 3 - - 3 3 - - - - -
Unidentified 10 28 21 17 23 20 8 20 27 32
Muscovite 2.82a
Talc 2.7a
Calcite 2.71a
Ice core data from Gaudichet et al. (1986, 1988). aPrimary mineral data from Deer et al. (1996).26
b Average of multiple values in Holeman (1965). cGaudichet et al. (1986) indicate primarily Ca and K27
feldspar (orthoclase and albite); Sala et al. (2008) found K-feldspar, therefore we use the average density28
of the two feldspars. dGaudichet et al. (1986) do not distinguish between pyroxenes and amphiboles, Sala29
et al. (2008) did not find pyroxenes, only amphibole therefore we use the hornblende average. eWada and30
Wada (1977)31
4
A.3. BET nano-scale32
DC coils
Magnetic Rod
Wire
Gold Sample Boat
Position Sensor
AC coils
Figure A1: Schematic of the ETH nano scale.
5
A.4. Raw data33
Data table includes concentrations of uranium, U, in ppt (ng/kg), the uranium activity34
ratio, (234U/238U); the radiogenic strontium, 87Sr/86Sr, and neodymium, 143Nd/144Nd,35
isotopic compositions; the surface area, SBET , and fractal dimension, D, values measured36
using the BET nano-scale (see below for description); the calculated recoil factors, f, and37
ages for each sample. Three sets of sample ages are calculated. One set of samples was38
measured prior to the availability of the nano-scale BET (starred); these sample ages were39
calculated by assigning the f values measured on the samples from the same depth with40
anf value error of 10%. These samples are noted in gray in Figure 2 of the main text.41
The second set of samples were measured using the initial set-up of the nano-scale BET42
(see discussion below), which provided some SBET values with high errors; errors in the43
calculated ages are as high as 50%. The final set of samples were measured show lower44
errors in SBET and correspondingly lower errors in the ages. Errors reported here are45
calculated based on a ”bootstrap” Monte Carlo approach.46
6
T
a
b
le
A
2
:
D
o
m
e
C
D
a
ta
*
S
am
p
le
U
2σ
( 234 U
/
2
3
8
U
) 2
σ
8
7
S
r/
8
6
S
r
2σ
1
4
3
N
d
/
1
4
4
N
d
2σ
S
B
E
T
2σ
D
2
σ
f
2
σ
a
g
e
2
σ
d
ep
th
(m
)
p
p
t
m
2
/
g
ka
11
2
(D
)
0.
03
3
10
n
.d
.
n
.d
.
11
2
(I
)
0.
05
1
9
1.
11
9
0
.7
0
9
0
8
1
1
0
0
n
.d
.
99
0
(D
)
1.
09
2
7
0
.7
0
9
4
6
2
4
0
0
.5
1
2
3
9
4
3
0
2
9
.9
8
1
.2
9
2
.3
5
5
0
.0
4
4
0
.1
5
8
4
0
.0
0
8
1
99
0
(I
)
0.
21
1
1
1.
28
1
1
0
.7
0
8
7
7
8
4
0
0
.5
1
2
4
8
0
1
0
0
8
3
1
6
10
40
(D
)
0.
79
4
2
0
.7
1
0
8
8
9
4
0
0
.5
1
2
5
1
2
2
5
n
.m
n
.m
.
10
40
(I
)
0.
30
1
1
1.
20
1
11
0
.7
0
8
8
4
5
4
0
0
.5
1
2
5
6
6
2
5
8
8
*
3
5
*
19
00
(D
)
1.
45
4
7
0
.7
0
9
4
1
6
4
0
0
.5
1
2
4
5
3
2
5
n
.m
.
n
.m
.
19
00
(I
)
0.
41
4
2
1.
38
9
13
0
.7
0
8
9
2
6
4
0
0
.5
1
2
5
1
3
2
5
2
5
6
*
7
4
*
19
01
(D
)
0.
82
3
8
0
.7
0
9
7
5
4
4
0
0
.5
1
2
4
9
9
2
5
3
4
.7
5
1
.3
9
2
.3
6
6
0
.0
1
2
0
.1
7
7
6
0
.0
0
8
1
19
01
(I
)
0.
23
2
3
1.
35
3
13
0
.7
0
9
0
7
2
4
0
0
.5
1
2
4
9
5
2
5
2
0
2
2
6
26
03
(D
)
1.
45
9
7
0
.7
0
9
8
5
6
1
0
0
.5
1
2
5
2
1
2
5
3
5
.6
2
1
.4
4
2
.3
4
8
0
.0
2
5
0
.1
9
2
2
0
.0
0
9
0
26
03
(I
)
0.
54
4
3
1.
35
9
12
0
.7
0
8
9
7
9
1
0
0
.5
1
2
5
6
9
1
0
0
3
1
1
4
8
26
04
(D
)
1.
21
8
8
0
.7
0
9
6
6
1
4
0
0
.5
1
2
5
1
6
1
2
n
.m
.
n
.m
.
26
04
(I
)
0.
48
8
3
1.
34
4
13
0
.7
0
8
6
0
3
4
0
0
.5
1
2
5
5
6
1
2
3
2
5
*
1
5
4
*
28
12
(D
)
1.
14
2
5
0
.7
0
9
5
5
4
4
0
0
.5
1
2
4
2
2
2
5
4
8
.0
6
1
.9
8
2
.3
9
5
0
.0
2
2
0
.2
2
5
0
0
.0
0
8
4
28
12
(I
)
0.
39
2
3
1.
49
8
13
0
.7
0
9
0
3
2
4
0
0
.5
1
2
4
9
1
5
0
4
2
1
6
5
28
13
(D
)
1.
03
6
4
0
.7
1
0
1
0
7
1
0
0
0
.5
1
2
4
7
9
1
2
n
.m
.
n
.m
.
28
13
(I
)
0.
59
3
2
1.
31
4
13
0
.7
0
8
9
3
1
1
0
0
0
.5
1
2
5
3
6
2
4
4
1
3
*
3
1
0
*
32
18
(D
)
1.
00
7
5
0
.7
0
9
0
2
7
2
0
0
.5
1
2
4
4
8
1
6
4
8
.8
4
0
.4
9
2
.5
5
2
0
.0
1
3
0
.1
4
3
0
0
.0
0
3
4
32
18
(I
)
0.
26
1
3
1.
49
8
14
0
.7
0
8
2
6
8
2
0
0
.5
1
2
5
5
2
2
0
7
2
3
1
9
1
32
20
(D
)
0.
82
6
4
0
.7
0
8
9
4
4
4
0
0
.5
1
2
4
5
0
2
0
4
8
.9
7
5
.8
8
2
.5
3
4
0
.0
1
3
0
.1
5
1
2
0
.0
1
8
5
32
20
(I
)
0.
23
5
1
1.
49
2
13
0
.7
0
8
2
0
5
3
0
0
.5
1
2
5
4
4
2
5
8
1
3
6
2
1
32
45
(D
)
0.
62
2
3
0
.7
0
9
5
8
7
4
0
0
.5
1
2
4
6
4
1
2
5
2
.9
7
5
.2
7
2
.5
7
3
0
.0
1
3
0
.1
4
5
8
0
.0
1
4
8
32
45
(I
)
0.
17
9
1
1.
47
5
14
0
.7
0
8
1
7
0
3
0
0
.5
1
2
5
8
1
1
0
0
8
7
0
6
2
4
32
46
(D
)
0.
71
9
2
0
.7
0
9
1
1
0
1
0
0
0
.5
1
2
4
4
4
1
2
4
9
.4
3
0
.7
4
2
.5
4
6
0
.0
1
3
0
.1
4
7
3
0
.0
0
3
9
32
46
(I
)
0.
18
7
1
1.
51
2
10
0
.7
0
7
9
7
3
4
0
0
.5
1
2
5
3
8
5
0
7
3
0
1
6
5
32
55
(D
)
4.
37
2
22
0
.7
0
8
6
0
3
4
0
0
.5
1
2
4
6
1
2
4
5
3
.1
5
0
.8
5
2
.5
7
7
0
.0
0
7
0
.1
4
4
6
0
.0
0
3
9
32
55
(I
)
0.
41
9
2
1.
42
1
14
0
.7
0
8
1
0
0
4
0
0
.5
1
2
5
6
4
2
0
8
2
6
7
0.708 0.7085 0.709 0.7095 0.71 0.7105 0.711 0.7115
0.512385
0.512410
0.512435
0.512460
0.512485
0.512510
0.512535
0.512560
0.512585
87Sr/86Sr
14
3 N
d/
14
4 N
d
2σ
M
od
er
n 
Se
aw
at
er
Figure A2: Dome C Sr and Nd isotopic compositions of dust (brown) and ice (blue). Also shown is the
range of modern surface seawater values for Sr (constant) and Nd (variable).
8
A.5. Surface Areas from Mineralogy47
9
Table A3: Compiled Surface Area Data
Mineral Size Range (µm) SBET Power Law Function
Illitea 108.54*d−0.528
< 2 119
< 2 99
< 63 13
< 63 25
Kaolinite 23.052*d−0.363
< 2 19 b
< 2 47 c
0.2 35 d
0.25 30 d
0.45 39 d
0.86 20 d
Chloritee 106.77*d−0.998
63 1.71
200 0.54
Smectiteb
(var Illite, Kaolinite) < 2 180
Quartz and Carbonate 3*d−0.772
< 2 3 f
50-125 0.1 g
Feldspar - Amphibole Mixtureh 34.117*d−0.69
15 8.46
60 1.12
100 1.23
200 0.77
350 0.68
750 0.46
Amorph Si (opal) i 144.47*d−0.579
< 2 - 5 85
5-10 40
Volcanic glass j 1.655*d−0.174
5 1.242
228 0.6713
842 .4896
4123 0.3938
Muscovite k 13.628*d−0.938
0.5 29.5
1.5 7.12
3.75 4.57
Talc 10.76*d−1.032
1 22 l
10 0.5 m
aUncles et al. (2006); bOmotoso and Mikula (2004); cHughes et al. (2009); dOrmsby and Shartsis (1960);
eBrandt et al. (2003); fBanin et al. (1975); gGautier et al. (2001); hWhite et al. (1996); iVan Bennekom
et al. (1991); jBourcier et al. (2000); kRaman and Mortland (1966);l Holland and Murtagh (2001);
mFerrer et al. (2001)
10
Figure A3: Functions Describing Variations in SBET with Grain Size. Red lines are the plotted power
law functions for each mineral. Gray shaded area is the lognormal distribution of the grain size. SBET
is shown for each mineral.
0 1 2 3 4 5 6 7 8 9 100
100
200
300
400
500
600
700
800
grain size (μm)
S B
ET SIllite = 49.786 m2/g
0 1 2 3 4 5 6 7 8 9 10
5
10
15
20
25
30
35
40
45
grain size (μm)
S B
ET
SKaolinite = 13.724 m2/g
0 1 2 3 4 5 6 7 8 9 100
100
200
300
400
500
600
grain size (μm)
S B
ET SChlorite = 27.38 m2/g
0 1 2 3 4 5 6 7 8 9 10
0
2
4
6
8
10
12
grain size (μm)
S B
ET
SQuartz = 1.004 m2/g
0 1 2 3 4 5 6 7 8 9 10
0
20
40
60
80
100
120
grain size (μm)
S B
ET
Sfeldspar-amph = 12.655 m2/g
0 1 2 3 4 5 6 7 8 9 100
500
1000
1500
2000
2500
grain size (μm)
S B
ET SOpal = 61.898 m2/g
11
0 1 2 3 4 5 6 7 8 9 10
1
1.2
1.4
1.6
1.8
2
2.2
2.4
grain size (μm)
S B
ET
SGlass=1.261 m2/g
0 1 2 3 4 5 6 7 8 9 100
10
20
30
40
50
60
70
grain size (μm)
S B
ET SMuscovite = 3.742 m2/g 
0 1 2 3 4 5 6 7 8 9 10
0
10
20
30
40
50
60
grain size (μm)
S B
ET
STalc = 2.656 m2/g
12
A.6. Local bed topography at Dome C48
Figure A4: Local topography (m a.s.l.) around Dome Concordia. Bedrock elevations have been obtained
by airborne and surface radar sounders (Forieri et al., 2005) (note that deviations of up to several 10
meters on an absolute scale are possible). The drilling site is marked by a dot in the center. All radar
sounding positions used to generate the map are marked with grey circles. A 25x25 point grid has been
interpolated with a Kriging method.
13
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Toward a radiometric ice clock: uranium ages of the Dome C ice core

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Toward a radiometric ice clock: uranium ages of the Dome C ice core

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