Probing methane in the high Canadian Arctic to understand methane on Mars

Two decades of CH₄ observations on Mars indicate a dynamic geochemical system not explained by known atmospheric or geological processes characterized by two behaviours: 1) episodic 'plumes' with detection levels of 2-40 ppbv; and 2) background < 1 ppbv levels with seasonal variation of a factor of 3 rising over the northern spring/summer and falling over the northern autumn/winter. Both of these behaviours are inconsistent with the ~300 year lifetime of CH₄ in the Martian atmosphere. CH₄ on Mars is of particular interest as ~70% of CH₄ of Earth is biogenic and the active CH₄ cycles on Mars remain a tantalizing biosignature potentially indicative of past or extant biological activity in the subsurface.

On Earth, near surface atmospheric CH₄ cycles are largely driven by two microbial processes: methanogens producing CH₄ and methanotrophs oxidizing CH₄ producing CO₂. In permafrost environments such as Axel Heiberg Island, Nunavut, Canada often used as a high-fidelity Mars analogue site, CH₄ flux varies seasonally with carbon-poor cryosols becoming a net methane sink in the spring and summer as the activity of CH₄ oxidizing bacteria increases. In addition to the seasonal cycle, hypersaline cold springs analogous to putative subsurface Martian brines, comprise active, point source CH₄ seeps. The Martian subsurface is the most likely environment to harbour extinct or even extant life and understanding the near surface expression of methanogenic and methanotrophic processes in terrestrial permafrost subsurface environments is key to the interpretation of the Martian CH₄ cycles as a potential biosignature. Of particular interest is the anerobic oxidation of methane (AOM) whereby the oxidation of CH₄ by methane oxidizing archaea is coupled to the reduction of sulphate by sulfate reducing bacteria in the absence of oxygen in submarine sediment hosted methane seeps. Recently, genetic evidence of AOM was detected in Lost Hammer Spring sediments, a cold spring CH₄ seep on Axel Heiberg Is. We used an Off-Axis Integrated Cavity Output Spectrometer capable of rapid, sub-ppb CH₄ measurements currently being developed by ABB Inc. as a potential CH₄ spectrometer for future landed Mars missions (see Moores et al. this conference) to measure near surface CH₄ in transects around Lost Hammer coordinated with biological sampling to characterize both subsurface AOM and the near surface expression of a methane seep in a terrestrial permafrost environment.