Radiocarbon Dating of Groundwater

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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

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low isotopic concentration 10-12-10-16 long
half-life
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Our Idea
Surface collected raw material high 10Be

Blade from Qesem Cave
low 10Be Deep quarried raw material
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Dendrochronology
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12.4 26 kyr BP marine data corals, foraminifera
0 -12.4 kyr BP Tree-Ring data set
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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
  d13C
• (13C/12C)sample-(13C/12C)sta
  ndard
• d13C -----------------------------------
  ---- x1000
• 
  (13C/12C)standard

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How does carbon and radiocarbon get in the
groundwater?
CO2(gas)root --- aq
100 pmc d13C -25
CaCO3
0 pmc d13C 0
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Different water environments
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Several alive specimen were measured with the
water were they lived
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How does carbon and radiocarbon get in the
groundwater?
CO2(gas)root --- aq
100 pmc d13C -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 d13C 0
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Hvinningdal Aquifer - Raised plain 80 m asl -
800 mm/y precipitation - gt200 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.
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18 wells analyzed. Tritium 15-62 TU post-bomb
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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
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Oxygen as possible candidate for organic material
oxidation
T ºC O2 mg/l 7 11.8 8
11.5 9 11.2
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n. 3.1, DOC ca. 3 mg/l
DOC ca. 0.3 mg/l
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high O2 high 14C
Low O2 low 14C
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Acorr diss Am(-25)/d13Cm
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F (44/32) (12-O2)/SCO2
Acorr dissOx Am(-25)/(d13Cm25 F)
Fluctuation in gw table
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• 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
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Radiocarbon Dating in Water Environments
Very important for -control and use of
hydrological resources -chronologies
Variables are several modeling is necessary