Spatiotemporal patterns of organic carbon burial over the last century in Lake Qinghai, the largest lake on the Tibetan Plateau

Lakes are important carbon sinks in terrestrial environments. However, the estimation of the global lake carbon sink has large uncertainty. Data from plateau and remote lakes are rare, and most studies of carbon sequestration in large lakes have been based on single or a few sediment cores. Here, twenty-five sediment cores were collected by grid sampling covering Lake Qinghai, the largest lake on the Tibetan Plateau. Age models were established by combining radionuclide 210Pb137Cs dating with magnetic susceptibility chronostratigraphy of sediment cores. Furthermore, the spatiotemporal variations of the organic carbon burial rate (OCBR) over the past century were investigated. The OCBR of Lake Qinghai has increased significantly since the 1990s in association with warm-humid climates, increased nutrient supply and, enhanced land-use changes. The spatial distributions of OCBR were insignificant during the 1900s–1960s and 1960s–1990s and then shifted to a pattern of high values occurring in the southwestern lake areas during the post-1990s period. The spatial distribution of OCBR was mainly determined by sediment mass accumulation rate, primary production, and potential mineralization. The average OCBR in the all sediment cores showed no correlation with water depth (12–30 m) and was within one standard deviation of the whole-lake average value for most cores. These results suggest that the average OCBR of a sediment core in a relatively flat lakebed can generally represent the whole-basin level of Lake Qinghai. The average OCBR was 22.5 ± 5.5 g m−2 yr−1, which is close to those values reported previously for lakes of boreal forest and taiga but significantly higher than those reported for tundra lakes. Our findings highlight that the remote lakes on the Tibetan Plateau have great carbon sequestration potential in sediments and may act as a significant natural carbon sink.