Freshwater radiocarbon reservoir age in the lower Yellow River floodplain during the late Holocene

The radiocarbon concentration of the dissolved inorganic carbon (DIC) pool of most freshwater bodies such as lakes and rivers tends to be depleted with respect to that of the contemporaneous atmosphere, resulting in an apparent radiocarbon age of inorganic carbon therein known as freshwater reservoir effect. This phenomenon of radiocarbon age offset is usually site specific and varies over time. By radiocarbon dating pairs of twigs and gastropod shells preserved in an ancient lake, as well as gastropod shells in pre-bomb flooding sediments of known age, we are able to determine the freshwater radiocarbon reservoir effect in the lower Yellow River floodplain during the late Holocene. The regional freshwater radiocarbon reservoir age ranges from 1081 to 233 years with an average of 575 ± 317 years, slightly older than that obtained from Lake Dongping by radiocarbon dating of live submerged aquatic plants. Our results show that the freshwater radiocarbon reservoir age is much older than its marine counterpart of the Yellow Sea and Bohai Bay. A source inversion using dual carbon isotopes (i.e. 14C and 13C) and a linear mixing model revealed that the DIC in the surface water bodies was mainly from shallow groundwater and the Yellow River. Our results have broad relevance to the geological and archaeological chronologies based on the radiocarbon method for this area.