Climate change and extreme hydroclimatic events primarily regulate sedimentary organic carbon sequestration in an alpine lake on the Tibetan Plateau

Long-term carbon sequestration dynamics of alpine lakes on the Tibetan Plateau under dual pressures from ongoing climate warming and frequent climatic extremes remain poorly understood. Here, we reconstructed century-scale organic carbon burial dynamics and identified organic carbon sources using molecular biomarkers ( n -alkanes) in Hedin Noel Lake, northern Tibetan Plateau. Results show organic carbon accumulation rates exhibited an overall increasing trend under a warmer and wetter climate over the past century, tracking variations in total organic carbon. It was primarily derived from aquatic macrophytes and terrestrial higher plants in the surrounding catchment. However, an extreme hydroclimatic event, evidenced by multiple sedimentary geochemical proxies, disrupted the prevailing organic carbon burial regime via rapid deposition of allochthonous organic-poor matter. This event, associated with the cascading outburst flood of upstream Zonag Lake in 2011, suppressed lake primary production, thereby undermining the carbon sequestration capacity. This study highlights that hydroclimatic events can critically control lake carbon sequestration, a process governed by the dual mechanisms of allochthonous inputs and the in-lake biological carbon pump. These findings provide important implications for regional carbon budget assessments across the Third Pole under a warming climate with increasing extremes.