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Radiocarbon Dating of Groundwater

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.

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Radiocarbon Dating of Groundwater

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  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. Cosmogenic Isotopes Cosmogenic Isotopes Cosmogenic Isotopes Isotope Main Target half-life 3He N,O stable 10Be N,O 1.6 Ma 26Al Ar 0.7 Ma 36Cl Ar 0.3 Ma 14C N 5730 y 32Si Ar 140 y 3H N,O 12.3 y Mineral 3He O, Mg, Si, Ca…Ol, Pyx, 10Be O, Si,.. Qtz, Ol,… 26Al Si,.. Qtz 36Cl Ca, K,… K-spar, calcite 14C O, Si… Qtz Isotope Main Target half-life 3He N,O stable 10Be N,O 1.6 Ma 26Al Ar 0.7 Ma 36Cl Ar 0.3 Ma 14C N 5730 y 32Si Ar 140 y 3H N,O 12.3 y Mineral 3He O, Mg, Si, Ca…Ol, Pyx, 10Be O, Si,.. Qtz, Ol,… 26Al Si,.. Qtz 36Cl Ca, K,… K-spar, calcite 14C O, Si… Qtz Isotope Main Target half-life 3He N,O stable 10Be N,O 1.6 Ma 26Al Ar 0.7 Ma 36Cl Ar 0.3 Ma 14C N 5730 y 32Si Ar 140 y 3H N,O 12.3 y Mineral 3He O, Mg, Si, Ca…Ol, Pyx, 10Be O, Si,.. Qtz, Ol,… 26Al Si,.. Qtz 36Cl Ca, K,… K-spar, calcite 14C O, Si… Qtz low isotopic concentration 10-12-10-16 long half-life

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

  4. EQUILIBRIUM n ~2 atoms/cm2/sec HOMOGENEOUSLY DISTRIBUTED CLOSED SYSTEM CO2 HCO3-- COMMON ELEMENT T1/2 5730 y

  5. NATURAL CHANGES OF 14C EQUILIBRIUM GEOMAGNETIC FIELD SOLAR ACTIVITY HOMOGENEOUSLY DISTRIBUTED CLIMATE ANTHROPOGENIC CHANGES OF 14C CLOSED SYSTEM NUCLEAR TESTS --- INCREASE OF 14C COMMON ELEMENT FOSSIL FUEL CONSUMPTION--- DILUTION OF 14C T1/2 5730 y

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

  7. 12.4 – 26 kyr BP marine data: corals, foraminifera 0 -12.4 kyr BP Tree-Ring data set

  8. 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

  9. CO2(aq) 100 pmc δ13C -25‰ 2HCO3 50 pmc δ13C -12.5 ‰ CaCO3 0 pmc δ13C 0 ‰ CO2(aq)+H2O+CaCO3 2HCO3- + Ca++ How does carbon and radiocarbon get in the groundwater? CO2(gas)root --- aq 100 pmc δ13C -25‰ CaCO3 0 pmc δ13C 0‰

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

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

  12. Melanopsis costata – costata (cc) – lives in the Jordan River (black) Melanopsis Buccinoidea (buc) – lives in streams and springs (white) 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

  13. “Water’ plant -32.5

  14. CO2(aq) 100 pmc δ13C -25‰ 2HCO3 50 pmc δ13C -12.5 ‰ CaCO3 0 pmc δ13C 0 ‰ CO2(aq)+H2O+CaCO3 2HCO3- + Ca++ How does carbon and radiocarbon get in the groundwater? CO2(gas)root --- aq 100 pmc δ13C -25‰ 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 CaCO3 0 pmc δ13C 0‰

  15. 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.

  16. 18 wells analyzed. Tritium 15-62 TU post-bomb

  17. <1 TU 18 wells analyzed. Tritium 15-62 TU post-bomb Matrix carbonate is negligible Strong disagreement with the T data n. 3.1 ? Boaretto et al., Radiocarbon 1998

  18. O2 + (CH2O)n CO2 + H2O Oxygen as possible candidate for organic material oxidation T ºC O2 mg/l 7 11.8 8 11.5 9 11.2

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

  20. high O2 high 14C Low O2 low 14C

  21. Acorr diss = Am(-25)/δ13Cm

  22. O2 + (CH2O)n CO2 + H2O F =(44/32) (12-[O2])/[ΣCO2] Acorr diss+Ox = Am(-25)/(δ13Cm+25 F) Fluctuation in gw table

  23. 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

  24. 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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