Permafrost rivers emit mostly pre-aged carbon on the Qinghai-Tibet Plateau under climate warming

Climate-sensitive alpine permafrost rivers on the Qinghai-Tibet Plateau export pre-aged carbon (C), yet the role of this pre-aged C in greenhouse gas emissions remains unclear. Here, through radiocarbon analysis of riverine CO 2 , CH 4 , dissolved organic carbon (DOC), and sediment organic carbon (SOC), we show that DOC and SOC originate primarily from pre-aged C, and it is more readily degraded than modern C due to lower aromaticity, with microorganisms preferentially metabolizing permafrost-derived fractions. Pre-aged C accounts for >60% of both CO 2 and CH 4 emissions. CO 2 derives mainly from pre-aged active layer C decomposition, with increased terrigenous fresh CO 2 input entering rivers during the growing season. Notably, ancient permafrost C contributes up to ∼30.5% of total CH 4 emissions. Our findings highlight that ancient C released by alpine permafrost rivers substantially contributes to greenhouse gas emissions, emphasizing the need to improve global C models and formulate climate-resilient mitigation frameworks to support sustainable development. • Riverine DOC and SOC are pre-aged on the Qinghai-Tibet Plateau • Riverine microorganisms preferentially metabolize pre-aged carbon with low aromaticity • Permafrost carbon contributes up to ∼30.5% of total CH 4 emissions • Pre-aged carbon accounts for >60% of both CO 2 and CH 4 emissions The Qinghai-Tibet Plateau (QTP) is an important permafrost carbon storage region where rivers provide direct conduits for processing and emitting ancient carbon to the atmosphere. This study is the first to quantify the contribution of ancient permafrost carbon decomposition to CO 2 and CH 4 emissions from QTP rivers. We show that riverine microorganisms preferentially decompose ancient permafrost carbon within bulk dissolved organic carbon and sediment organic carbon. Permafrost and pre-aged active layer carbon decomposition contribute >60% to total carbon emissions, with permafrost carbon accounting for up to ∼30.5% of CH 4 emissions. Our results indicate that considerable mineralization of permafrost carbon occurs in alpine permafrost rivers, suggesting a potential risk of ancient carbon release under climate warming. The permafrost carbon-climate feedback mechanism on the Qinghai-Tibet Plateau represents a critical yet understudied component of the global climate system. This study demonstrates that riverine CH 4 and CO 2 emissions in this region are fueled primarily by the decomposition of pre-aged carbon with low aromaticity. Notably, permafrost-derived carbon contributes up to 30.5% of total CH₄ emissions. These findings underscore the urgent need to reassess the role of ancient carbon cycling in alpine permafrost rivers to support sustainable development in a warming climate.