A freshwater old carbon offset in Lake Baikal, Siberia and problems with the radiocarbon dating of archaeological sediments: Evidence from the Sagan-Zaba II site

Lake Baikal in Eastern Siberia is one of the largest and deepest freshwater lakes in the world, and its diverse fauna were extensively utilized by local human populations over many millennia. The regional culture history models primarily are based on radiocarbon dates on human skeletal remains, and in some cases, also on dates on sediments from habitation sites. Analyses of a set of 113 radiocarbon dates from the Sagan-Zaba Holocene hunter-gatherer and pastoralist habitation site (52.6825° N, 106.4760° E) on the western coast of Lake Baikal demonstrates two critical problems in the dating of these sets of materials. First, comparison of AMS radiocarbon dates on terrestrial mammal and Baikal seal bones from Sagan-Zaba reveals the existence of a freshwater radiocarbon offset in the seal remains of at least 700 radiocarbon years. Radiocarbon dates on skeletal remains from humans who consumed the aquatic fauna also should be expected to carry an old carbon offset. Second, comparison of radiocarbon dates made on sediment samples with those made on terrestrial mammal bones demonstrates major inconsistencies. The primary problem with these samples is that the carbon being dated in them is of unclear relationship to human activities of interest at the site. Therefore, the still common practice in this region of radiocarbon dating sediments to establish archaeological chronologies should be abandoned. The AMS radiocarbon dating of bone from species which clearly fed outside of Lake Baikal's aquatic environments should provide more reliable age estimates for human activities at archaeological sites.