Is methane being released from Norwegian glaciers? 

Recent research underscores a potential, yet overlooked, positive climate feedback mechanism: the transport of subglacially produced methane (CH4) to the atmosphere via meltwater. While the majority of research focused on release from beneath the Greenland Ice Sheet, mountain glaciers have been largely understudied, creating a gap in our understanding of the spatial distribution of subglacial CH4 emissions. Emerging research from glaciers in Iceland, Canada, Alaska, and China suggests the presence of CH4 release also from glaciers other than the Greenland Ice Sheet.   Here, we explore the potential of CH4 release from outlet glaciers of the Jostedalsbreen ice cap and Midtdalsbreen in central Norway. We investigated whether meltwaters from outlet glaciers of Jostedalsbreen (Tuftebreen, Fåbergstølsbreen, Bøyabreen, Supphelebreen, Austerdalsbreen and Nigardsbreen), along with Midtdalsbreen in Finse, act as a source of CH4 to the atmosphere. We collected discrete samples for dissolved CH4 (dCH4) and CO2 concentrations at all glacier outlets multiple times throughout the melt season. Additionally, we conducted longer time-series measurements of dCH4 at Tuftebreen, Fåbergstølsbreen and Midtdalsbreen, utilizing custom-made dCH4 sensors. Accompanying these measurements were samples analysed for water chemistry and stable isotopes of dCO2 (δ13C-CO2) in samples where concentrations were elevated compared to atmospheric equilibrium.   Our results indicate that dCH4 concentrations in the meltwater of all studied glaciers remained below atmospheric equilibrium concentrations throughout the melt season. In contrast, dCO2 concentrations surpassed atmospheric equilibrium levels, suggesting that the studied glacial runoffs do not act as CH4 source to the atmosphere but might contribute as a small source of CO2. This dataset of dissolved greenhouse gases enhances our understanding of the spatial distribution of subglacial CH4 emissions, fostering discussions on carbon cycling beneath glaciers and the factors influencing the presence or absence of CH4 emissions from the subglacial domain.