Evaluation of lacustrine organic δ13C as a lake-level indicator: A case study of Lake Qinghai and the satellite lakes on the Tibetan Plateau

In recent years, the sedimentary delta(13)Corg values have been recognized to be indicative of lake-level changes in lakes on the Tibetan Plateau (TP). However, the sensitivity of sedimentary delta(13)Corg to lake-level changes and the potential relationship between lake-level variations and climatic forces are still unknown in this particular region. Here, we systematically evaluate sedimentary delta(13)Corg as a proxy of lake-level changes in lakes with different sizes on the TP. Consistent with previous studies, the total organic matter of sediments was mainly contributed by aquatic plants in lakes on the TP. In the studied lakes, sedimentary delta C-13 values mainly reflect lake-level changes, as the species of aquatic plants with different delta(13)Corg values strongly respond to lake level. However, sedimentary delta C-13 values are much more sensitive to lake-level changes in a moderate-depth lake (similar to 10 m) than those in a deep lake (27 m) or a shallow lake (< 3-5 m). In other words, the sedimentary delta(13)Corg may not effectively record lake-level changes on the TP when the lakes are deep (not sensitive) or shallow (only submerged plants). This relationship can be clearly seen in the case study in cores HY15 and GH02. The sedimentary delta(13)Corg trend in core HY15 was well correlated with the observed lake-level changes over the past 50 yr in Lake Qinghai. Based on the hypothesis that delta(13)Corg is indicative of lake-level changes, the lake-level change showed obvious millennial-scale oscillations in Lake Gahai (moderate lake) during the Holocene, but there were no obvious lake-level oscillations in Lake Qinghai (deep lake). In addition, the variation in the TOC/ON ratio suggested that sedimentary delta(13)Corg was often influenced by the contribution of terrestrial plants in Lake Gahai during the Holocene. Therefore, although delta(13)Corg was a very sensitive proxy of lake-level changes in lakes with maximum water depths ranging from 5 m to 20 m in lakes on the northeastem TP, we should consider the possible contribution of terrestrial plants when the sedimentary delta(13)Corg value is used as indicator of lake-level changes.