Impact of hydrological conditions on the radiocarbon reservoir effect in lake sediment 14C dating: the case of Kusai Lake on the northern Qinghai-Tibet Plateau

The hydrological conditions of a lake system strongly influence the reservoir effect in the radiocarbon dating of endogenic organic and inorganic carbon in lake sediments. In this paper, we compare C-14 dating with varve counting results for cores from Kusai Lake to determine the temporal changes in C-14 reservoir ages during the last 2000 years. Based on the C-14 budget equation for a lake system, the characteristics of geomorphology, topography, and river systems in the catchment, and the physical and chemical properties of modern water in Kusai Lake, the hydrological conditions and the reservoir effect age are discussed. The reservoir age of the sediment core from northwestern Kusai Lake (i.e., deep water area) fluctuates slightly between 2980 and 3310 years, while that from southeastern Kusai Lake (i.e., shallow water area) fluctuates greatly between 3130 and 4010 years. Under the relatively steady conditions of atmospheric C-14 levels for the past 2000 years, the C-14 level in the dissolved inorganic carbon (DIC) of Kusai Lake is mainly related to carbon influxes from river and glacial meltwater and carbon outfluxes in lake water. The water in the shallow water area is more affected by the Kusai River, glacier meltwater, and lake outflow than the water in the deep water area, which has caused larger temporal changes in the radiocarbon reservoir ages in the shallow water area than in the deep water area during the last 2000 years.