Reservoir effect or C14 dating of marine organisms

The CIRAM laboratories, specialists in Carbon 14 dating, date and analyze materials found in archaeological contexts.

The Carbon 14 is the radioactive isotope found in all living organisms. When an organism dies, the radiocarbon content decreases, because carbon-14 is no longer renewed through exchanges due to respiration or photosynthesis. It is considered that it takes 5568 years for an organism to lose half its radiocarbon content. Normally, for the C14 dating of an organism, it is enough to measure the decrease of 14C to obtain a reliable result. But for marine organisms, certain factors must be taken into account.

Compared to atmospheric carbon dioxide, seawater is 14C-poor. Exchanges at the surface and deep in the water are slower. It is noted that the carbon-14 content varies according to location. This phenomenon that complicates dating is called the reservoir effect.

Our scientists also analyze and date marine organisms despite the reservoir effect that imbalances the radiocarbon content according to depth and geographical areas.

The reservoir age represents the age difference between a marine sample and a terrestrial sample dating from the same period. This gap was found thanks to the dating of shells whose year of death is known and compared with cross-dating between contemporary shells around the world: this result allowed us to find an average ageing value of 400 years, and this for all the so-called superficial oceanic waters.

Beware, however, that the distribution of Carbon 14C in the oceans is not homogeneous, it depends on several factors such as the size of the basin, latitude or even atmospheric exchanges. It is constant for example that the C14 content decreases at depth. It is important to be attentive also to specific areas such as deltas or estuaries that possess a modified geochemical composition partly due to the mixing between freshwater carbon and marine water carbon.

Study and analysis of organisms in marine environments

The geographical origin of the artifact thus remains an important element to associate the adapted corrective factor and to propose an accurate dating. For some artifacts carved in cetacean bones, the origin remains uncertain, so we will have to be satisfied with using the reference average of 400 years.

It is possible to obtain the correction factors according to the geographic location of the artifact on the Marine 2020 Reservoir Database site. This allows you to calculate an average correction using reference points close to the object's assumed origin.

Analysis of uncertain materials

For unknown, or uncertain materials, our scientists rely on stable carbon and nitrogen isotope analysis by isotope ratio mass spectrometry (IRMS). This method allows us to differentiate between terrestrial and marine organisms in order to apply, or not, the correction reserved for marine artifacts.

CIRAM, specialist in C14 dating of marine organisms

CIRAM scientists remain at your disposal and deliver all the necessary advice to formalize the best analytical protocols to be used in order to bring an adequate answer to your problems.