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 0CalBP

Calibrated date

0BP

5000BP

10000BP

15000BP

20000BP

25000BP

30000BP

Rad

ioca

rbon

dete

rmin

ati

on

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

14

C p

mc

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

14

C p

mc

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 2

NH 1

NH 3

SH

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

14

C p

mc

18 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

Aco

rr p

mc

dissol

Acorr diss = Am(-25)/δ13Cm

20

40

60

80

100

120

140

160

20 40 60 80 100 120Am pmc

Aco

rr p

mc

oxid+dissol

dissol

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

Aco

rr p

mc

oxid+dissol

dissol 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