Methane

Drainage basin

Ecology

Biology

Geotechnical engineering

Cartography

Discharge

Arctic ice pack

Cryosphere

Inflow

Melt pond

Geology

Oceanography

Greenhouse gas

Geography

Hydrology (agriculture)

Sea ice

Environmental science

Estuary

Atmospheric sciences

Arctic

Drift ice

Carbon dioxide

Geophysical Research Letters

We present a year‐round time series of dissolved methane (CH 4 ), along with targeted observations during ice melt of CH 4 and carbon dioxide (CO 2 ) in a river and estuary adjacent to Cambridge Bay, Nunavut, Canada. During the freshet, CH 4 concentrations in the river and ice‐covered estuary were up to 240,000% saturation and 19,000% saturation, respectively, but quickly dropped by &gt;100‐fold following ice melt. Observations with a robotic kayak revealed that river‐derived CH 4 and CO 2 were transported to the estuary and rapidly ventilated to the atmosphere once ice cover retreated. We estimate that river discharge accounts for &gt;95% of annual CH 4 sea‐to‐air emissions from the estuary. These results demonstrate the importance of resolving seasonal dynamics in order to estimate greenhouse gas emissions from polar systems.

River Inflow Dominates Methane Emissions in an Arctic Coastal System