Marine Reservoir Corrections: An overview

 

Radiocarbon samples which obtain their carbon from a different source (or reservoir) than atmospheric carbon may yield an apparent age called a reservoir age. The Ocean has a reservoir age of about 402 radiocarbon years (see Stuiver et al. 1986). This apparent age 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. The reservoir age is incorporated in the modelled marine curve of Stuiver et al. (1998).

Regionally, the 14C of the ocean surface deviates from this modelled marine curve due to variations in upwelling, ocean currents, and inter-hemispheric atmospheric 14C. Therefore, when dating marine shells it is essential to know the difference (ΔR) between the modelled radiocarbon age of surface water and the known 14C age of surface water at that time represented by the marine shell sample. The ΔR for a specific location (s) can be calculated from known age shells, collected prior to atmospheric bomb testing using the formulae:

Rs(t) – Rg(t) = ΔR(s)

Where Rs(t) is the 14C age of known-age sample and Rg(t) is the 14C age of the model mixed ocean layer for the calendar year (AD) of the known-age sample. The ΔR standard error is calculated by the formulae:

ΔRσ = √(σRs(t)2 + σRg(t)2)

 

More information on suitable shellfish for radiocarbon dating can be found here.

 

References

Stuiver M, Reimer PL, Braziunas TF, 1998. High-precision radiocarbon age calibration for terrestrial and marine samples. Radiocarbon, 40(3): 1127-1154.

Stuiver M, Pearson GW, Braziunas TF, 1986. Radiocarbon Age Calibration of Marine Samples Back to 9000 cal yr BP. Radiocarbon, 28(2B): 980-1021.