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

Presentation #403.09 in the session Into the Unknown: Astrobiology and Habitability.

Published onOct 20, 2022
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.

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