Co-ebullition of CO₂ and CH₄: Unveiling a hidden carbon emission pathway in the World's Third Pole.

Ebullition is a well-established pathway for methane (CH₄) emissions from aquatic systems. Here, we report a previously overlooked but consequential phenomenon, "co-ebullition", the joint release of carbon dioxide (CO₂) and CH₄ within gas bubbles. Based on a comprehensive investigation of dissolved greenhouse gas concentrations and emissions across major rivers (Yarlung Zangbo, Lancang, Yangtze, Yellow) on the Qinghai-Tibet Plateau (QTP), we demonstrate that >90% of bubbling CO₂ is co-released with ebullitive CH₄, while nitrous oxide (N₂O) remains predominantly diffusive (>99.0%). This co-ebullition constitutes approximately 34.1% of the total CO₂ emissions within QTP river systems, revealing a previously unrecognized flux in these climate-critical headwaters. By contrast, paired monitoring of downstream non-plateau river reaches shows co-ebullition rarely occurs in lowland fluvial networks, which we use as a comparative control to interpret the unique plateau-specific environmental drivers of coupled carbon bubble emission. We further establish that this process is triggered by low atmospheric pressure and high turbulent flow over distinctive double-layer bed structures (e.g., gravel-clay). Our findings identify the QTP rivers as global hotspots of coupled carbon ebullition and unravel co-ebullition as a pivotal mechanism in carbon cycles of climate-sensitive alpine and polar ecosystems.