Variability of the 14C reservoir effects in Lake Tangra Yumco, Central Tibet (China), determined from recent sedimentation rates and dating of plant fossils

Sediments from lakes provide one of the most important archives for past environmental changes on the Tibetan Plateau. The recent sedimentation rate of modern lakes is widely used as an independent method to calibrate 14C-derived chronologies because 14C values are often affected by a reservoir effect. Terrestrial plant residues in lake sediments are believed to be the ideal material for 14C dating because they normally provide the true ages of the sediments. In this study, we present the spatial and temporal variations in modern sedimentation rates over the past ∼150 years and evaluate the reservoir effects of 14C ages determined from bulk sediments and plant residues from Lake Tangra Yumco on the central Tibetan Plateau. The results show that ages determined from plant residues are systematically younger than those of the bulk sediments. However, the reservoir effects associated with the bulk sediments are much more constant than those of the plant residues, highlighting the complicated composition of these macro-remains and the fact that they might not be the best dating materials in Tangra Yumco, especially in southern part. A similar reservoir effect of ∼2200 years is observed in the southern and northern parts of Tangra Yumco, based on the dating of modern surface sediments and aquatic plants. This study demonstrates the complexity of the reservoir effect in a closed lake on the Tibetan Plateau, and careful consideration must be paid to the use of different approaches to date different materials in order to establish a reliable chronology.