Quantifying The Impact of Recent Climate Change on Sedimentary Biogeochemical Cycles and The Organic Carbon Sink

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Global warming is modifying the storage and release of organic carbon (OC) in the Arctic environment both on land and at sea. To understand how climate change influences the Arctic carbon cycle, it is necessary to understand its journey from release by permafrost thaw to final destination, in the atmosphere or in the seafloor. The Mackenzie watershed and Beaufort Shelf is a key region that is affected by changing Arctic conditions and which may be an indicator of what will happen across the broader Arctic. When permafrost thaws, it releases OC that has been accumulating frozen for thousands of years, all at once. Microbes living in soil, lakes, streams and the sea, can then use this OC to grow by degrading it into greenhouse gases (GHG) such as carbon dioxide or methane, leading to more warming and, more thaw, in a positive feedback. Microbes use electron acceptors such as oxygen, nitrate, manganese, iron oxides and sulfate to degrade OC. In the seafloor, OC is likely to degrade into carbon dioxide. On land, electron acceptors are often scarce and microbes ferment OC into methane gas, which is a more potent greenhouse gas. The place, and the pathway taken to degrade OC therefore has a direct impact on the climate and can exacerbate warming. Rapid shift in biogeochemical cycles, have been observed in response to the recent warming trends, which may affect OC degradation. My long-term research goal is to forecast the responses and feedbacks between microbial-sedimentary systems and the changing Arctic. Two short-term (5-year) science objectives are (1) quantify the present and the historical distribution of organic carbon (OC) mineralization on the Beaufort shelf and the fate of marine and terrestrial sources and (2) balance the carbon budgets of production and emissions of greenhouse gases from sites undergoing abrupt permafrost thaw. Both (1) and (2) are at the forefront of Arctic research and are experimentally accessible due to the development and fine-tuning of new techniques and multidisciplinary international collaborations. The analytical program relies on the sampling of porewater, sediment and gas from field sites and analysis of microbial catabolic rates with both stable and radioactive isotope tracers in the lab. Results are then incorporated in diagenetic models that considers deposition rates, chemical fluxes in porewater and gas migration. Stable isotopes of carbon and sulfur play a critical role in this analysis. The program will anticipate changes in the carbon sink of the Mackenzie-Beaufort fluvial system. It ties into pan-Arctic assessments of OC transport, burial and degradation. This could shape government policy and relations between Arctic nations. The program is the proving ground for nine HQP that will increase their capacity to conduct respectful research alongside local communities. It will maintain Canada at the forefront of Arctic scientific research and a leader in assessing the consequences of climate change.