The Arctic is one of the most climatically sensitive areas on Earth – heating up at least twice as fast as the global average in response to anthropogenic warming. Such warming drives strong positive feedbacks, e.g., by stimulating methane (CH4) release in this region. CH4 is one of the most powerful greenhouse gases within our atmosphere, about 34 times more potent than carbon dioxide over 100 years (Etminan et al., 2016). Although of pivotal importance for an accurate prediction of future climate change, current CH4 budgets and emission predictions are inflicted with large uncertainties. In the proposed research, I seek to address this major knowledge gap by investigating microbial CH4 turnover dynamics in the modern and, more importantly, the past Canadian Arctic. The Arctic is a key area to study potential climate-methane feedbacks, because unequivocal environmental changes, such as increasing temperature, greater riverine input, and enhanced thaw of permafrost, that may ultimately impact CH4 emissions, occur.

The first stage of this project will specifically focus on tracing microbial CH4 turnover dynamics in the modern Beaufort Sea and Mackenzie River Delta lakes, testing organic proxy techniques by integrating biomarker analyses, (isotope-) biogeochemical measurements, and molecular approaches (DNA, RNA sequencing). CH4 concentration and stable isotope ratios will be measured in the lakes, the Beaufort Sea water column, as well as surface sediments, and data will be combined with incubation experiments, to constrain the source of CH4, and to quantify its production and oxidation by microorganisms. In addition, microorganisms from the lakes and Beaufort Sea water column will be sequenced to identify the key microbial actors of the production, and oxidation of CH4 – an important process that regulates how much CH4 reaches the atmosphere. The activity of the most important microorganisms will then be linked to the presence and abundance of known specific lipid biomarkers (molecules that may be used as proxies to indicate the environmental conditions within the geologic record), to obtain a calibrated framework to study past CH4 dynamics in the region.
The second phase of the project, where PhD student Madeleine Santos  is in charge, will focus on past CH4 dynamics in the Arctic, using lipid biomarkers from the first “calibration” phase. Two relevant time intervals will be targeted: (1) the last 12,000 years, which will allow insights into the longer-term variation in CH4 turnover in the context of “slow” environmental changes (temperature and sea-level rise) associated to the transition from glacial to current interglacial conditions, and (2) the last 50 to 200 years, allowing us to assess whether the anthropogenic-driven temperature increase recorded in the region has enhanced aquatic CH4 production and oxidation."