title: Lower groundwater ¹⁴C age by atmospheric CO₂ uptake during sampling and analysis.
abstract: Uptake 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.
authors.affiliation: Isotope Hydrology Section, International Atomic Energy Agency, Vienna, Austria.
authors.forename: Pradeep K
authors.initials: PK
authors.lastname: Aggarwal
authors.forename: Luis
authors.initials: L
authors.lastname: Araguas-Araguas
authors.forename: Manzoor
authors.initials: M
authors.lastname: Choudhry
authors.forename: Michel
authors.initials: M
authors.lastname: van Duren
authors.forename: Klaus
authors.initials: K
authors.lastname: Froehlich
mesh_terms: D001272:Atmosphere; D002245:Carbon Dioxide; D002250:Carbon Radioisotopes / Q000032:analysis*; D004784:Environmental Monitoring / Q000379:methods*; D060587:Groundwater / Q000032:analysis*; D013397:Sudan
chemical_list: D002250:Carbon Radioisotopes; D002245:Carbon Dioxide