Research Project

The freshwater reservoir effect (FRE) may produce anomalously old radiocarbon ages of the samples from lakes and rivers. This includes the bones of people whose subsistence was based on freshwater fish, shells or snails, but also the pottery in which these foods were cooked (Bronk Ramsey 1998; 2009; Philippsen 2013; Cook et al. 2015). The marine reservoir effect is a well-known and fairly well understood phenomenon. Radiocarbon ages of samples from the open seas around Denmark, for example, can be corrected by subtracting 400 years. The freshwater reservoir effect, in contrast, is elusive, complex and variable in time and space, from one region to another. Generally speaking, water rich in dissolved ancient calcium carbonates, commonly known as hard water, is the most common reason for the FRE. It is therefore also called hard-water effect. Although it has been known for more than 60 years, it is still less well-recognized by archaeologists than the marine reservoir effect, which strongly affects the correct chronological placement of some archaeological finds (Philippsen 2013).

The general assumption in radiocarbon dating is that the dated sample had been in equilibrium with the atmosphere so that its initial radiocarbon concentration is known. The lower the measured radiocarbon concentration compared to the initial concentration, the older the sample. However, there are reservoirs with lower radiocarbon levels than the atmosphere. These include the oceans and freshwater systems like lakes and rivers. Samples originating from these reservoirs have low radiocarbon concentrations to begin with (Bronk Ramsey 2009; Philippsen 2012; 2013; Cook et al. 2015). This age deviation is called reservoir age, and the effect that causes it, marine reservoir effect or freshwater reservoir effect. It affects the radiocarbon dates obtained on the omnivores species that can feed on aquatic food (e.g. fishes, shells, snails, aquatic plants, etc.), but could be present in the sediment levels, irrespective of the site’s distance to the coast (Philippsen 2012).

The project scope is to examine the order of magnitude and degree of variability of the FRE over short and long timescales in Lower Danube Basin, the segment Vedea River - Danube Delta. The demonstration model will be the method and technology used to achieve the presence of the FRE, and the product developed and validated will be the FRE calibration for this area, and open-source calibration package, which will be integrated with the R statistical environment Bchron and rcarbon packages. That will help establishing the correct 14C ages for samples collected from archaeological sites or landscape and environment located in their proximity, and will represent the experimental testing of the proposed methodology and technology together with the developed product.

The approach is complex and ambitious and proposes a different kind of investigation from what is currently available in Romania.