East-west divergence in Holocene organic carbon accumulation of Tibetan Plateau lakes: Roles of climate and organic matter sources

With the increasing prominence of carbon emissions and the intensification of global warming, the carbon cycle and carbon accumulation have drawn widespread attention. Lake carbon accumulation is a crucial component of the terrestrial carbon cycle, significantly influencing local climate change and atmospheric carbon dioxide levels. The Tibetan Plateau (TP), renowned for its high elevation, numerous alpine lakes, and large carbon storage in sediments, is a key area for studying lake organic carbon accumulation. However, the carbon accumulation rate (CAR) of lakes on the TP exhibits strong spatial variability, and the driving mechanisms vary across regions, especially in the western TP, which has been poorly studied. To understand the driving mechanisms of climate and human activities on lake CAR across the TP, we collected 33 sediment cores, including 15 from the western TP, and calculated the CAR during the Holocene. Our results show that the average CAR of lakes on the TP during the Holocene was 6.13 g C m⁻² yr⁻¹. Through relational cluster analysis, lakes were classified into two groups, with an east - west distribution pattern separated by the 90°E meridian. In eastern lakes, CAR is closely related to temperature and precipitation, while in western lakes, it is mainly influenced by wind strength. This difference is attributed to the distinct sources of organic matter in lake sediments. In eastern lakes, total organic carbon (TOC) comes from both aquatic and terrestrial plants. Higher temperatures and more precipitation promote terrestrial vegetation growth in the watershed, increasing sediment TOC content and accelerating sediment accumulation rate (SAR). In contrast, in western lakes with lower temperatures and less precipitation, TOC mainly originates from aquatic plants. Thus, temperature and precipitation changes have a minor impact on TOC, and lake sedimentation is mainly affected by wind dynamics, resulting in a negative correlation between precipitation and CAR. Additionally, the CAR of all lakes on the TP is negatively correlated with lake area and depth. Under continued warming, the CAR of eastern TP lakes is likely to increase, with small and shallow lakes playing a significant role.