Sink or source? Methane and carbon dioxide emissions from cryoconite holes, subglacial sediments, and proglacial river runoff during intensive glacier melting on the Tibetan Plateau

Abstract High Mountain Asia glaciers are currently ignored in the estimation of global greenhouse gas budgets (e.g., methane (CH4) and carbon dioxide (CO2)). Similar to the Asian Water Tower and Third Pole, the Tibetan Plateau (TP) hosts the largest volume of glaciers outside the polar regions. These glaciers contain large reservoirs of organic carbon that can influence glacial ecosystems under rapid melting. However, no data exist on the current footprint of CH4 and CO2 from glaciers in the TP. Here, we report in situ observations of CH4 and CO2 fluxes for glacial cryoconite holes, subglacial sediments, and proglacial river runoff across the TP. Our results indicate that cryoconite holes and subglacial sediments can accelerate the export of greenhouse gasses during the melting season due to intensive glacier melting. However, to some extent, proglacial river runoff can be a significant sink of atmospheric CO2; this fact was not identified in previous studies. Our findings suggest that variations (source or sink) of greenhouse gasses from TP glacial basins should be considered in regional CH4 and CO2 budgets under climate warming.