After splitting the cores, collecting the sediment samples, and label, weight, and dry them, the moment has come to investigate their age. To do this we applied a Radiocarbon Dating method. This radiometric
dating method uses the naturally occurring radioisotope 14C to estimate
the age in those materials that contain carbon (e.g. organic matter, textiles,
carbonates, wood). This method, however, can only be applied to date
materials that are less than ~55-60 thousand years old, after this period the
radioactive decay (the rate in which 14C decays into a non radiometric carbon
isotope) is such that there is not enough 14C in the materials to calculate an
age.
Radiocarbon measurements are traditionally performed by counting the radioactive decay of individual carbon atoms via gas proportional counting or via liquid scintillation counting. However, for small samples decay counting is relatively insensitive and subject to large statistical uncertainties.
In our case, as we dated samples of biogenic carbonate from the planktic foraminifera collected from the sediments, and as foraminifera are very small and their shells don’t weight much (in addition that only ~12% of calcium carbonate corresponds to carbon atoms) we can’t use proportional counting or liquid scintillation. Thus, we applied a technique called Accelerator Mass Spectrometry (AMS). This technique detects and counts the 14C atoms directly. How? Samples for radiocarbon AMS measurements are incinerated. The resulting C02 is collected and reduce to a solid carbon (graphite) target for sputtering atomic carbon ions into a mass spectrometer, which allows dating samples containing only a few milligrams of carbon.
Radiocarbon measurements are traditionally performed by counting the radioactive decay of individual carbon atoms via gas proportional counting or via liquid scintillation counting. However, for small samples decay counting is relatively insensitive and subject to large statistical uncertainties.
In our case, as we dated samples of biogenic carbonate from the planktic foraminifera collected from the sediments, and as foraminifera are very small and their shells don’t weight much (in addition that only ~12% of calcium carbonate corresponds to carbon atoms) we can’t use proportional counting or liquid scintillation. Thus, we applied a technique called Accelerator Mass Spectrometry (AMS). This technique detects and counts the 14C atoms directly. How? Samples for radiocarbon AMS measurements are incinerated. The resulting C02 is collected and reduce to a solid carbon (graphite) target for sputtering atomic carbon ions into a mass spectrometer, which allows dating samples containing only a few milligrams of carbon.
