Methane (CH4) and nitrous oxide (N2O) are major, long-lived greenhouse gases (GHG), which foster global warming and significantly impact atmospheric chemistry dynamics. As a vast component of the Earth System, the aquatic realm is key for the balance between sources and sinks of these gases and largely determines their contribution to the global radiative balance. Hence, understanding the mechanisms of production, consumption, and emissions of these aquatic GHG is crucial for improving predictions of their future changes with ongoing climate change.

While the overall distribution of CH4 and N2O across the water column and sediments in marine, estuarine, and lacustrine systems is well documented, understanding of GHG cycling and emissions in the aquatic realm remains a major scientific challenge. This is largely due to the complex interactions between geological, oceanographic/limnological, biological, and anthropogenic processes. Furthermore, although it is well established that CH4 and N2O emissions offset natural CO2 uptake by aquatic systems, the magnitude of this counteracting effect, as well as their temporal and spatial variability, is still highly uncertain.

This session invites contributions addressing recent advances in understanding the biogeochemical cycling, microbial pathways, and fluxes of CH4 and N2O in aquatic environments. We welcome studies based on laboratory and mesocosm experiments, field observations, remote sensing and modelling approaches. Topics of interest include, but are not limited to:

• CH4 and N2O cycling in estuaries, bays, fjords, coastal lagoons and other transitional water bodies across all latitudes, as well as fluxes across the sediment-water(ice)-air interfaces.

• The role of current and projected environmental perturbations such as eutrophication, deoxygenation and warming as drivers of CH4 and N2O cycling at the land-ocean continuum (e.g. through riverine input and submarine groundwater discharge).

• The impact of extreme events (e.g. heat waves, storms, floods) on CH4 and N2O cycling and emissions.

• CH4 and N2O formation, transport, and consumption, including specific microbial processes involved.

• Microbe-mineral and microbe-animal interactions (including symbioses) and how these affect CH4 and N2O turnover.

• Quantification of the contribution of CH4 and N2O emissions to overall radiative balance of aquatic systems.