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Radiocarbon Dating of Groundwater Elisabetta Boaretto Radiocarbon Dating and Cosmogenic Isotopes Laboratory Kimmel Center for Archaeological Sciences,

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Presentation on theme: "Radiocarbon Dating of Groundwater Elisabetta Boaretto Radiocarbon Dating and Cosmogenic Isotopes Laboratory Kimmel Center for Archaeological Sciences,"— Presentation transcript:

1 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

2 Isotope Main Target half-life 3 He N,O stable 10 Be N,O 1.6 Ma 26 Al Ar 0.7 Ma 36 Cl Ar 0.3 Ma 14 C N 5730 y 32 Si Ar 140 y 3 H N,O 12.3 y Mineral 3 He O, Mg, Si, Ca…Ol, Pyx, 10 Be O, Si,.. Qtz, Ol,… 26 Al Si,.. Qtz 36 Cl Ca, K,… K-spar, calcite 14 C O, Si… Qtz Cosmogenic Isotopes low isotopic concentration long half-life Isotope Main Target half-life 3 He N,O stable 10 Be N,O 1.6 Ma 26 Al Ar 0.7 Ma 36 Cl Ar 0.3 Ma 14 C N 5730 y 32 Si Ar 140 y 3 H N,O 12.3 y Mineral 3 He O, Mg, Si, Ca…Ol, Pyx, 10 Be O, Si,.. Qtz, Ol,… 26 Al Si,.. Qtz 36 Cl Ca, K,… K-spar, calcite 14 C O, Si… Qtz Cosmogenic Isotopes Isotope Main Target half-life 3 He N,O stable 10 Be N,O 1.6 Ma 26 Al Ar 0.7 Ma 36 Cl Ar 0.3 Ma 14 C N 5730 y 32 Si Ar 140 y 3 H N,O 12.3 y Mineral 3 He O, Mg, Si, Ca…Ol, Pyx, 10 Be O, Si,.. Qtz, Ol,… 26 Al Si,.. Qtz 36 Cl Ca, K,… K-spar, calcite 14 C O, Si… Qtz Cosmogenic Isotopes

3 Our Idea low 10 Be Deep quarried raw material Surface collected raw material high 10 Be Blade from Qesem Cave

4 n ~2 atoms/cm 2 /sec CO 2 HCO 3 -- EQUILIBRIUM HOMOGENEOUSLY DISTRIBUTED COMMON ELEMENT CLOSED SYSTEM T 1/ y

5 EQUILIBRIUM HOMOGENEOUSLY DISTRIBUTED COMMON ELEMENT T1/ y CLOSED SYSTEM GEOMAGNETIC FIELD SOLAR ACTIVITY CLIMATE NATURAL CHANGES OF 14 C ANTHROPOGENIC CHANGES OF 14 C FOSSIL FUEL CONSUMPTION--- DILUTION OF 14 C NUCLEAR TESTS --- INCREASE OF 14 C

6 Dendrochronology Sample from a living tree Building a tree-ring chronology Dead tree on ground Standing dead tree Bristlecone pine

7 12.4 – 26 kyr BP marine data: corals, foraminifera kyr BP Tree-Ring data set

8

9 Radiocarbon Activity is expressed in Pmc: percent modern carbon Age is calculated with the Decay Law Precision of % = years Range 50,000 year (LSC 60,000 year) Isotopic fractionation between 12 C, 13 C and 14 C: δ 13 C ( 13 C/ 12 C) sample -( 13 C/ 12 C) standard δ 13 C = x1000 ( 13 C/ 12 C) standard

10 How does carbon and radiocarbon get in the groundwater? CO 2(gas)root --- aq CaCO 3 CO 2(aq) +H 2 O+CaCO 3 2HCO Ca ++ CO 2(aq) 100 pmc δ 13 C -25 CaCO 3 0 pmc δ 13 C 0 2HCO 3 50 pmc δ 13 C pmc δ 13 C pmc δ 13 C 0

11 Different water environments Mediterranean Coast Kinneret with Ohalo II Dead sea and Lisan lake stalg Lisan Med Coast 14 C and U-Th

12 Lake Kinneret Using modern (alive) and fossil material, water

13 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) Melanopsis Saulcyi (sa) – lives in springs and streams, south of the Sea of Galilee Several alive specimen were measured with the water were they lived

14 Water plant -32.5

15 How does carbon and radiocarbon get in the groundwater? CO 2(gas)root --- aq CaCO 3 CO 2(aq) +H 2 O+CaCO 3 2HCO Ca ++ CO 2(aq) 100 pmc δ 13 C -25 CaCO 3 0 pmc δ 13 C 0 2HCO 3 50 pmc δ 13 C pmc δ 13 C pmc δ 13 C 0 14 C 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

16 Hvinningdal Aquifer - Raised plain 80 m asl 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 - O 2 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.

17 18 wells analyzed. Tritium TU post-bomb

18 18 wells analyzed. Tritium TU post-bomb n. 3.1 ? <1 TU Matrix carbonate is negligible Strong disagreement with the T data Boaretto et al., Radiocarbon 1998

19 Oxygen as possible candidate for organic material oxidation T ºC O 2 mg/l O 2 + (CH 2 O) n CO 2 + H 2 O

20 n. 3.1, DOC ca. 3 mg/l DOC ca. 0.3 mg/l

21 Low O 2 low 14 C high O 2 high 14 C

22 A corr diss = A m (-25)/δ 13 C m

23 Fluctuation in gw table A corr diss+Ox = A m (-25)/(δ 13 C m +25 F) F =(44/32) (12-[O2])/[ΣCO 2 ] O 2 + (CH 2 O) n CO 2 + H 2 O

24 nitrate CONCLUSION Most of the sample A corr 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

25 Radiocarbon Dating in Water Environments Very important for: -control and use of hydrological resources -chronologies Variables are several modeling is necessary


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