I think the original application of a non-equilibrium model resulted from the reservoir effect of the ocean. This lessor concentration of oceanic C-14 compared to atmospheric C-14 is what was viewed as evidence that C-14 supported a young earth. "The ocean is still catching up with the atmosphere and hasn't reached equilibrium yet", was the YEC interpretation.
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This apparent age of oceanic water is caused both by the delay in exchange rates between atmospheric CO2 and ocean bicarbonate, and the dilution effect caused by the mixing of surface waters with upwelled deep waters which are very old (Mangerud 1972). A reservoir correction must therefore be made to any conventional shell dates to account for this difference. Reservoir corrections for the world oceans can be found at the Marine Reservoir Correction Database, a searchable database online at Queen's University, Belfast and the University of Washington.
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