View
56
Download
0
Category
Tags:
Preview:
DESCRIPTION
Radiocarbon Dating of Groundwater . Elisabetta Boaretto Radiocarbon Dating and Cosmogenic Isotopes Laboratory Kimmel Center for Archaeological Sciences, Weizmann Institute of Science and Dept of Land of Israel Studies and Archaeology Bar Ilan University. Cosmogenic Isotopes. - PowerPoint PPT Presentation
Citation preview
Radiocarbon Dating of Groundwater
Elisabetta Boaretto
Radiocarbon Dating and Cosmogenic Isotopes LaboratoryKimmel Center for Archaeological Sciences ,
Weizmann Institute of Scienceand
Dept of Land of Israel Studies and ArchaeologyBar Ilan University
Isotope Main Target half-life
3He N,O stable10Be N,O 1.6 Ma26Al Ar 0.7 Ma36Cl Ar 0.3 Ma14C N 5730 y32Si Ar 140 y 3H N,O 12.3 y
Mineral3He O, Mg, Si, Ca…Ol, Pyx, 10Be O, Si,.. Qtz, Ol,…26Al Si,.. Qtz36Cl Ca, K,… K-spar, calcite14C O, Si… Qtz
Cosmogenic Isotopes
low isotopic concentration 10-12-10-16
long half-life
Isotope Main Target half-life
3He N,O stable10Be N,O 1.6 Ma26Al Ar 0.7 Ma36Cl Ar 0.3 Ma14C N 5730 y32Si Ar 140 y 3H N,O 12.3 y
Mineral3He O, Mg, Si, Ca…Ol, Pyx, 10Be O, Si,.. Qtz, Ol,…26Al Si,.. Qtz36Cl Ca, K,… K-spar, calcite14C O, Si… Qtz
Cosmogenic IsotopesIsotope Main Target half-life
3He N,O stable10Be N,O 1.6 Ma26Al Ar 0.7 Ma36Cl Ar 0.3 Ma14C N 5730 y32Si Ar 140 y 3H N,O 12.3 y
Mineral3He O, Mg, Si, Ca…Ol, Pyx, 10Be O, Si,.. Qtz, Ol,…26Al Si,.. Qtz36Cl Ca, K,… K-spar, calcite14C O, Si… Qtz
Cosmogenic Isotopes
Our Idea
low 10Be
Deep quarried raw material
Surface collected raw material
high 10Be Blade from Qesem Cave
n
~2 atoms/cm2/sec
CO2 HCO3
--
EQUILIBRIUM
HOMOGENEOUSLY DISTRIBUTED
COMMON ELEMENT
CLOSED SYSTEM
T1/2 5730 y
EQUILIBRIUM
HOMOGENEOUSLY DISTRIBUTED
COMMON ELEMENT
T1/2 5730 y
CLOSED SYSTEM
GEOMAGNETIC FIELDSOLAR ACTIVITY
CLIMATE
NATURAL CHANGES OF 14C
ANTHROPOGENIC CHANGES OF 14C
FOSSIL FUEL CONSUMPTION--- DILUTION OF 14C
NUCLEAR TESTS --- INCREASE OF 14C
90
100
110
120
130
140
150
160
170
180
190
200
1950 1960 1970 1980 1990 2000
year
14 C value (pM
C)
14C input (Harkness) fromnuclear test
Dendrochronology
Sample from a living tree
Building atree-ringchronology
Dead treeon ground
Standingdead tree
Bristlecone pine
Atmospheric data from Reimer et al (2004);OxCal v3.10 Bronk Ramsey (2005); cub r:5 sd:12 prob usp[chron]
25000CalBP 20000CalBP 15000CalBP 10000CalBP 5000CalBP 0CalBPCalibrated date
0BP
5000BP
10000BP
15000BP
20000BP
25000BP
30000BPRa
dioc
arbo
n de
term
inat
ion
12.4 – 26 kyr BP marine data: corals, foraminifera
0 -12.4 kyr BP Tree-Ring data set
Atmospheric data from Reimer et al (2004);OxCal v3.10 Bronk Ramsey (2005); cub r:5 sd:12 prob usp[chron]
1300CalBC1200CalBC1100CalBC1000CalBC900CalBC 800CalBC 700CalBC
Calibrated date
2500BP
2600BP
2700BP
2800BP
2900BP
3000BP
Rad
ioca
rbon
det
erm
inat
ion
14C age : 2750±30BP 68.2% probability 920BC (68.2%) 840BC 95.4% probability 980BC (95.4%) 820BC
Radiocarbon
• Activity is expressed in Pmc: percent modern carbon• Age is calculated with the Decay Law• Precision of 0.5-0.3% = 40-25 years • Range 50,000 year (LSC 60,000 year)• Isotopic fractionation between 12C, 13C and 14C: δ13C
(13C/12C)sample-(13C/12C)standard
δ13C = --------------------------------------- x1000 (13C/12C)standard
How does carbon and radiocarbon get in the groundwater?
CO2(gas)root --- aq
CaCO3
CO2(aq)+H2O+CaCO3 2HCO3- + Ca++
0
20
40
60
80
100
-25 -20 -15 -10 -5 0
d13C %o
14C
pm
c
CO2(aq) 100 pmc δ13C -25‰
CaCO3 0 pmc δ13C 0 ‰
2HCO3 50 pmc δ13C -12.5 ‰
100 pmc δ13C -25‰
0 pmc δ13C 0‰
Different water environments
Mediterranean Coast
Kinneret with Ohalo II
Dead sea and Lisan lake
stalg
stalg
Lisan
Med Coast
Med Coast
14C and U-Th
Lake Kinneret
Using modern (alive) and fossil material, water
Melanopsis Buccinoidea (buc) – lives in streams and springs (white)
Melanopsis costata – costata(cc) – lives in the Jordan River (black)
Melanopsis costata – jordanica (cj) -lives in the Sea of Galilee (black)
MelanopsisSaulcyi (sa) –lives in springsand streams,south of the Sea of Galilee
Several alive specimen were measured with the water were they lived
“ Water’ plant -32.5
How does carbon and radiocarbon get in the groundwater?
CO2(gas)root --- aq
CaCO3
CO2(aq)+H2O+CaCO3 2HCO3- + Ca++
0
20
40
60
80
100
-25 -20 -15 -10 -5 0
d13C %o
14C
pm
c
CO2(aq) 100 pmc δ13C -25‰
CaCO3 0 pmc δ13C 0 ‰
2HCO3 50 pmc δ13C -12.5 ‰
100 pmc δ13C -25‰
0 pmc δ13C 0‰
14C in groundwater
- Relative ages between aquifers
- Aquifer-flow velocities
- Study of mixed system
- Establishment of flow modes which are related to environmental problems connected with recent pollution
Hvinningdal Aquifer
- Raised plain 80 m asl- 800 mm/y precipitation- >200 mm/y ca. recharge - Matrix: Tertiary quartz sand covered with quaternary meltwater sand/gravel- Low carbonate, some tertiary lignite and reworked black org material- pH ca. 6- T 8-10 ºC- O2 12 mg/l saturation value- Some wells have nitrate-Tritium (15-62 TU) is present in almost all the wells indicating post-bomb groundwater origin.
14C Nuclear test peak
0.95
1.05
1.15
1.25
1.35
1.45
1.55
1.65
1.75
1.85
1.95
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
year
14C
Fra
ctio
n %
NH 2NH 1NH 3SH
18 wells analyzed.Tritium 15-62 TU post-bomb
0
20
40
60
80
100
120
-25.0 -20.0 -15.0 -10.0 -5.0 0.0
d13C%o
Am
14C
pm
c18 wells analyzed.Tritium 15-62 TU post-bomb
n. 3.1 ? <1 TU
Matrix carbonate is negligible
Strong disagreement with the T data
Boaretto et al., Radiocarbon 1998
Oxygen as possible candidate for organic material oxidation
T ºC O2 mg/l 7 11.8 8 11.5 9 11.2
O2 + (CH2O)n CO2 + H2O
n. 3.1, DOC ca. 3 mg/l
DOC ca. 0.3 mg/l
Low O2 low 14C
high O2 high 14C
20
40
60
80
100
120
140
160
20 40 60 80 100 120Am pmc
Acor
r pm
cdissol
Acorr diss = Am(-25)/δ13Cm
20
40
60
80
100
120
140
160
20 40 60 80 100 120Am pmc
Acor
r pm
c
oxid+dissoldissol
Fluctuation in gw table
Acorr diss+Ox = Am(-25)/(δ13Cm+25 F)
F =(44/32) (12-[O2])/[ΣCO2]
O2 + (CH2O)n CO2 + H2O
20
40
60
80
100
120
140
160
20 40 60 80 100 120Am pmc
Acor
r pm
c
oxid+dissoldissol nitrate
CONCLUSION•Most of the sample Acorr is above or close to 100 pmc ---- agreement with Tritium
•Extremely low value 32 pmc is due probably to fresh exposure of organic material to atmosphere
• Nitrate contribution to oxidation of organic matter
•Age: not more than few hundreds year
0 TU
Radiocarbon Dating in Water Environments
Very important for: -control and use of hydrological resources
-chronologies
Variables are several
modeling is necessary
Recommended