Isotopic Analysis of Dissolved CO2 and CH4 in a Coastal Permafrost Zone

The steady rise in global temperature is likely to perturb the cycling and transfer of carbon in the coastal Arctic. Given the high carbon content of Arctic soils, this region may become an increasingly important source of methane (CH4) and carbon dioxide (CO2) in response to permafrost loss in coming decades. We present targeted observations along a lake to bay system during the spring thaw around Cambridge Bay, in the coastal Canadian high Arctic. In this system, greenhouse gases produced in the freshwater environment are transported to the bay, where they may undergo further transport, transformation, or ventilation to the atmosphere. As warming alters the timing and dynamics of the ice retreat, carbon sources may shift and the magnitude of outgassing may change. We investigate the sources and pathways of the dissolved CO2 and CH4 via radio- and stable carbon isotope analyses, and conduct a spatial survey using a sensor suite containing a dissolved gas extractor, greenhouse gas analyzer, conductivity-temperature-depth probe, and oxygen optode. Across the transect, observed CH4 ranged from 1-5900 ppm, with δ13C values ranging from -70 to -47‰ (mean: -61.1±10.5‰); CO2 ranged from 100-3350 ppm, with δ13C values of -12 to +38‰ (mean: 6.1±13.1‰). Isotopic depletion of 13C correlated with lower CH4, while enrichment consistent with a primary productivity signal was seen in lower CO2 concentrations. Isotopic signatures additionally clustered with habitat type, revealing spatial variability in the processes controlling the production and transformation of CH4. Radiocarbon dating of the dissolved gases indicated predominantly modern carbon sources at all locations, with the high-CH4 melt ponds containing the youngest carbon (mean age of CH4: 148±16 years; mean age of CO2: 252±16 years). This work aims to enhance our understanding of interannual variability in the carbon cycle dynamics at this site, and to assess the system’s response to a changing climate.