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Studies show that the residence time of carbon 14 in the atmosphere ranges between 6 years and 10 years while the residence time of carbon 14 in oceans could take thousands of years.
Upwelling is another phenomenon that dilutes radiocarbon content of surface waters.
– Fees are inclusive of d13C and d18O measurements done in an isotope ratio mass spectrometer (IRMS), quality assurance reports, calendar calibration when applicable, and 24/7 web access to past results and pending analyses.
The rapid exchange of carbon between the atmosphere and the biosphere via the carbon dioxide pathway is not exactly the same between the atmosphere and the oceans.
Coastline shape, local climate and wind, and ocean bottom topography also contribute to upwelling.
The slow mixing and the upwelling of deep waters mean that the surface water of oceans already have apparent radiocarbon age relative to the atmosphere.
If the material is quite old (20 ky), it is possible that long-term exposure to the atmosphere can bias the result in the more recent direction by some unknown degree.
When it is necessary to extract carbonates by drilling or powdering specific areas of the material (especially those suspected to be very old – greater than 20 ky), we recommend that the drilling be done under an inert gas (like N2, Ar, etc.) and that the material be stored in very small vials and sent to us without delay.
This carbon exchange usually affects the shell’s exterior.