Lateral and air-water inorganic carbon and methane fluxes in a small Arctic river: Seasonal variations and the connections with local hydrology.

The importance of rivers to the global carbon cycle is well recognized, and the need for more measurements from historically understudied systems including Arctic rivers is essential in reducing bias. The proximity of Freshwater Creek to the community of Iqaluktuuttiaq (Cambridge Bay), Nunavut, Canada, makes it an excellent site for time-series study that appreciates pronounced seasonality. This detailed investigation acquired data representative of the river's annual cycle, including the dynamic spring melt season. Freshwater Creek exported 3.12 Gg C y-1 as DIC and 848 kg C y-1 as dissolved CH4 to the downstream coastal ocean. The river was a net emitter of CO2 that released (net) 22.0 Mg C y-1 to the atmosphere, but also experienced periods of CO2 uptake. CH4 emissions were 450 kg C yr-1, and all fluxes exhibited strong seasonality with maximum concentrations and fluxes during breakup. The significance of breakup was evident; half of the annual DIC and CH4 exported to the ocean occurred within 21-31 and 8-13 days of the onset on breakup respectively. DIC/CO2 and CH4 fluxes in Freshwater Creek are connected to local hydrology, thus changes to the water cycle with climate change will influence the timing and magnitude of carbon fluxes in this system. Our detailed account of seasonal variability will be a useful framework for similar systems that cannot be monitored all year, will provide context for the interpretation of existing data, and will aid in developing sampling plans with intention to observe a river's full range of conditions.