Dissolved methane and carbon dioxide fluxes in Subarctic and Arctic regions: Assessing measurement techniques and spatial gradients

• High resolution measurements revealed strong spatial heterogeneities in CH4 and CO2 fluxes.
• Highest dissolved CH4 and CO2 values were isolated covering <12% of the total study area.
• Substantial errors in regional extrapolations can be incurred if non-uniformity of fluxes is ignored.

Here we use a portable method to obtain high spatial resolution measurements of concentrations and calculate diffusive water-to-air fluxes of CH4 and CO2 from two Subarctic coastal regions (Kasitsna and Jakolof Bays) and an Arctic lake (Toolik Lake). The goals of this study are to determine distributions of these concentrations and fluxes to (1) critically evaluate the established protocols of collecting discrete water samples for these determinations, and to (2) provide a first-order extrapolation of the regional impacts of these diffusive atmospheric fluxes. Our measurements show that these environments are highly heterogeneous. Areas with the highest dissolved CH4 and CO2 concentrations were isolated, covering less than 21% of the total lake and bay areas, and significant errors can be introduced if the collection of discrete water samples does not adequately characterize these spatial distributions. A first order extrapolation of diffusive fluxes to all Arctic regions with similar characteristics as Toolik Lake suggests that these lakes are likely supplying 0.21 and 15.77 Tg of CH4 and CO2 to the atmosphere annually, respectively. Similarly, we found that the Subarctic Coastal Ocean is likely supplying 0.027 Tg of CH4 annually and is taking up roughly 524 Tg of CO2 per year. Although diffusive fluxes at Toolik Lake may not be as substantial when comparing against present seep ebullition and spring ice-out values, warming in the Arctic may result in the increase of methane discharge and methane emissions to the atmosphere. Thus further work is needed to understand this changing environment. This study suggests that high spatial resolution measurement protocols, similar to the one used here, should be incorporated into field campaigns to reduce regional uncertainty and refine global emission estimates.