Groundwater Dating with Environmental Tracers

Groundwater Dating with Environmental Tracers

Groundwater Dating with Environmental Tracers: Recent Developments and Applications
Werner Aeschbach Hertig
Werner Aeschbach‐Hertig
Institut für Umweltphysik
DPG, Dresden, 2011
Universität Heidelberg
Outline
• Overview of environmental tracer methods
– Principles and age ranges
Principles and age ranges
• New developments and examples of applications
– Natural SF6: China and India
– 14C and noble gases: China, Belgium, India
g
, g
,
– 81Kr, 39Ar: Development of a new analytical method
Recent Special Journal Issues on Environmental Tracers / Dating
• Select. papers from G
Select papers from G‐DAT
DAT '08:
08: Groundwater Dating Using ETs Groundwater Dating Using ETs
Isotopes in Environ. & Health Studies, Vol. 46, Issue 3, 2010
Insights from Environmental Tracers in Groundwater Systems
• Insights from Environmental Tracers in Groundwater Systems
Hydrogeology Journal, Vol. 19, Issue 1, 2011 2
Overview
of environmental tracer methods
Principles and age ranges
Principles and age ranges
3
Time Ranges of Dating Methods
water isotopes
dissolved gases
noble gas isotopes
solute isotopes
222Rn
SF6
CFCs
85Kr
3H
3H
H-3He
39Ar
14C
4He
81Kr
36Cl
10-22
10-11
100
101
102
103
104
105
106
dating range [a]
4
Applications of Dating Methods
groundw. topic
quality monitoring
nitrate pollution
organic pollution
vulnerability
source of water
recharge
dating tracer
O-18
tritium
tritium/He-3
CFCs, SF6
Kr-85
C-14 DIC
others
mixing ratios
flow and evolution
resource evaluation
surf.water interaction
catchment runoff proc.
methodology
0
10
20
30
40
50
60
70
80
number
b off studies
t di
Newman et al., 2010. Isotopes in Environ. & Health Studies, 46(3): 259 – 278
5
Principles of Dating Methods
radioactive decay
accumulation
Cinitial ?
4
He
con
ncentration
H,
14
C
39
Ar, 81Kr
Cosmogenic Radioisotopes
os oge c ad o so opes
con
ncentration
3
= accumulation rate ?
Radiogenic Isotopes
ad oge slope
c so
opes
40
time
time
input variation
mother - daughter pair
3
He
concenttration
concentrration
3
Tritium‐Helium
3
CFC-12
H
85
Kr
Transient Tracers
H
1950
time
Ar
1960
1970
1980
year
1990
2000
6
New
D l
Developments
t
and
Applications
a) Natural SF
)
6: China and India
7
China: Study Area
North China Plain
Central Plain
Age < 40 a
A
40
3H‐3He
Age 20 –
Age
20 – 30 ka
30 ka
14C
8
Groundwater Depletion in the NCP (unconfined) Groundwater table /
decline ∼ 1 m/a
Kendy et al., 2004. Hydrol. Process. 18: 2289‐2302.
9
3H‐3He Age Profile
3H‐
H 3He age increases with depth below WT →
H
i
ith d th b l WT
relative vertical velocity: ∼
l ti
ti l l it
15 /
1.5 m/a
von Rohden et al., 2010. Water Resour. Res., 46, W05511, doi:10.1029/2008WR007660.
10
Groundwater Balance in the North China Plain
velocities v
(m/a)
unsaturated
saturated
Darcy fluxes q
q = nv n ≈ 0 2
q = nv, n ≈ 0.2
Water table decline:
1
0.2
Velocity relative to WT:
y
= recharge rate R
1.5
0.3
25
2.5
05
0.5
TTotal vertical velocity:
l
i l l i
= withdrawal by pumping (for irrigation: I)
Deficit in water balance (storage depletion):
ΔS = R ‐ I = P ‐ ET in m/a: 0.2 = 0.3 ‐ 0.5 = 0.5 ‐ 0.7
11
Comparison SF6 – 3H
SF6 present 3H = 0
where h
H 0
Æ natural source of SF6
von Rohden et al., 2010. Isotopes in Environ. & Health Studies, 46(3): 279 – 290.
12
Excess SF6 versus 3H‐3He Age
Estimation of cterr:
Estimation of c
cterr = cmeas ‐ ceq ‐ cexc
Correlation with age
Correlation with age
→ Continuous accumu‐
lation along flowline
lation along flowline
New: Significant terrigenic SF6 in sedimentary aquifer!
New: Significant terrigenic SF
in sedimentary aquifer!
von Rohden et al., 2010. Isotopes in Environ. & Health Studies, 46(3): 279 – 290.
13
India: Study Area
Cambay Basin
14
Excess SF6 in India
Cambay Basin, y
,
India:
Terrigenic SF
Terrigenic
SF6
excess concentrated in certain depth layers. Wieser, 2010. PhD thesis, Univ. Heidelberg. 15
New
Developments
and
Applications
pp ca o s
b) 14C and noble gases: China, Belgium, India
16
P
xi
T, S
T
Ci
Ai
Air
W
Water
Dissolved noble gas
concentrations in
equilibrium with air:
Ci,eq = βi ( T, S ) pi
Bunssen Solubility β [ccm3STP ccm-3 atm--1]
The Noble Gas Thermometer
0.2
Xe
0.15
0.1
Kr
0.05
Ar
0
Ne
He
0
5
10
15
20
25
30
Temperature [°C]
17
China: Age Scale for Paleoclimate Records
3H‐3He dated
14C dated
Kreuzer et al., 2009. Chem. Geol. 259: 168‐180.
18
China: Noble Gas Paleotemperature Record
13 4 ± 1.1
13.4 ±
1 1 °C
C
ΔT = 4.6 °C
°
8.7 ± 0.4 °C
Kreuzer et al., 2009. Chem. Geol. 259: 168‐180.
19
14C in Groundwater: Dead Carbon Correction
14C Dating of Groundwater is based on dissolved inorganic carbon. Problem: Dissolution of carbonate adds "dead" carbon, decreasing A0.
Several "classical"
Several classical correction models exist, using chemistry and δ
correction models exist using chemistry and δ13C. C
Often no good agreement between models.
Approach used in recent Approach
used in recent
noble gas studies:
• Estimate recharge g
water composition (pH, HCO3, δ13C, …) based on assumed
based on assumed recharge conditions (pCO2, T, open/closed)
A14C ≈ 100 %
δ13C ≈ ‐25 ‰
"Recharge water" A14C ≈ 50 %
δ13C ≈ ‐12 ‰
A14C ≈ 0 %
δ13C ≈ 0 ‰
• New: Use NGT information to define ggroups with different p
recharge conditions
20
Example of Groundwater 14C‐Dating: Belgium
Ledo‐Paniselian Aquifer
Various infiltration waters used: Blaser et al., 2010. Appl. Geochem., 25: 437–455
Blaser et al., 2010. Appl. Geochem. 25: 437–455.
21
Belgium: Noble Gas Paleotemperature Record
ΔT ≈ 9.5 °C
Ledo‐Paniselian Aquifer, Belgium
Blaser et al., 2010. J. Quaternary Sci. 25: 1038–1044.
22
India: Noble Gas Paleotemperature Record
28.7 °C
ΔT = 3.5 °C
25.2 °C
Wieser, 2010. PhD thesis, Univ. Heidelberg. Paper in prep.
23
Groundwater Noble Gas Studies Worldwide
ΔT Holocene – LGM < 5 °C
C
ΔT Holocene – LGM ~ 5 °C
ΔT Holocene – LGM > 5 °C
24
New
Developments
and
Applications
pp ca o s
c) 81Kr, 39Ar: Development of a new analytical method
25
Noble Gas Radioisotopes: New Perspectives?
Available isotopes and their applications
counting possible
85
• Kr (T
Kr (T1/2
= 10 76 yr):
/ = 10.76 yr): – Dating of young groundwaters (< 50 yr)
~ 50'000 at/L
– Dating of upper ocean and lake waters
Dating of upper ocean and lake waters
•
•
39Ar (T
Ar (T
counting very hard
== 269 yr): 269 yr):
– Dating of deep ocean circulation
– Dating of groundwaters of intermed. age
Dating of groundwaters of intermed age
81Kr (T
K (T
1/2
~ 7'000 at/L
counting impossible
= 229'000 yr): 229'000 )
– Dating of old groundwaters (> 30'000 yr)
– Dating of polar ice cores
D ti
f l i
1/2
AMS? No: Negative ions unstable! ~ 1'000 at/L
26
New Method: Atom Trap Trace Analysis (ATTA)
source
atoms
laserlight
hν ħk
hν,
Principle of ATTA
Laser Cooling:
Slowing
g ((cooling)
g) of
atoms by multiple photon
absorption
Isotopically selective due
to resonance condition
and very large number of
absorbed photons
Chen et al., 1999.
Science 286, 1139-1141.
27
ATTA Team Heidelberg
Collaboration of Environmental and Atom Physics
Atom Physics
Goal: Develop ATTA for Goal:
Develop ATTA for 39Ar
Status: Dedicated atom trap system operational (enriched Status:
Dedicated atom trap system operational (enriched 39Ar)
Welte et al., 2010. New Journal of Physics 12, doi:10.1088/1367‐2630/12/6/065031
28
ATTA: Timeline
Milestones in ATTA Development for Groundwater Dating
• 1999: Demonstration of principle for Kr‐isotopes Chen et al., 1999, Science 286, 1139‐1141. "Ultrasensitive Isotope Trace Analyses with a Magneto‐Optical Trap"
p
y
g
p
p
• 2004: First practical application of 81Kr
Sturchio et al., 2004, Geophys. Res. Lett. 31, doi:10.1029/2003GL019234.
p y
"One million year old groundwater in the Sahara revealed by 81Kr and 36Cl"
• 2009: Precise spectroscopy of 39Ar transitions for laser cooling Welte et al., 2009. Rev. Sci. Instrum. 80, 113109, doi:10.1063/1.3257691. "Hyperfine spectroscopy of the 1s5−2p9 transition of 39Ar"
• 2011
2011: First detection of Fi d
i
f 39Ar at natural levels
A
ll l
Jiang et al., 2011, Phys. Rev. Lett. 106, doi: 10.1103/PhysRevLett.106.103001. "39Ar Detection at the 10‐16 Isotopic Abundance Level with ATTA"
29
Summary
Environmental Tracers for Groundwater Dating
• Large number of dating tracers, wide age range
• Use:
Use: Velocities, recharge rates, process rates, pollution, Velocities recharge rates process rates pollution
age scale for paleoclimate reconstruction, …
• SF6 affected by natural source also in sediments
•
14C dating can be improved by using NGT information
C dating can be improved by using NGT information
• ATTA for 39Ar: Progress, but still some way to go…
30
Thank You!