Radiocarbon dating of medieval bones can be off by centuries due to fish
Words of warning about radiocarbon dating medieval human bones
Danish monastic burials show elevated nitrogen-15, indicating freshwater fish consumption. The reservoir effect can make radiocarbon dates appear anomalously old, sometimes predating the convent's construction by centuries. The authors warn that without stable isotope analysis and proper correction, medieval human bones from aquatic diets can yield misleading chronologies across Europe.
Freshwater reservoir offsets can vary extremely, from zero to very high numbers – numbers up to 1000 years have been observed.