Lower Groundwater 14C Age by Atmospheric CO2 Uptake During Sampling and Analysis

Ground Water - Tập 52 Số 1 - Trang 20-24 - 2014
Pradeep Aggarwal1, Luis Araguás‐Araguás1, Manzoor Ahmad Choudhry1, M. van Duren1, K. Froehlich1
1Isotope Hydrology Section, International Atomic Energy Agency, Vienna, Austria

Tóm tắt

AbstractUptake of atmospheric CO2 during sample collection and analysis, and consequent lowering of estimated ages, has rarely been considered in radiocarbon dating of groundwater. Using field and laboratory experiments, we show that atmospheric CO2 can be easily and rapidly absorbed in hyperalkaline solutions used for the extraction of dissolved inorganic carbon, resulting in elevated 14C measurements. Kinetic isotope fractionation during atmospheric CO2 uptake may also result in decrease of δ13C, leading to insufficient corrections for addition of dead carbon by geochemical processes. Consequently, measured 14C values of groundwater should not be used for age estimation without corresponding δ13C values, and historical 14C data in the range of 1 to 10% modern Carbon should be re‐evaluated to ensure that samples with atmospheric contamination are recognized appropriately. We recommend that samples for 14C analysis should be collected and processed in the field and the laboratory without exposure to the atmosphere. These precautions are considered necessary even if 14C measurements are made with an accelerator mass spectrometer.

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Ground Water

Tập 52 Số 1

20-24

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