SEMINAR: OI Seminar Series - Isabelle Laurion

Title: Canadian thaw ponds under a warming climate

Abstract: Permafrost soils store half of the global below ground organic carbon stock, which is now being mobilized as peat soils thaw and erode. Part of the mobilized C is emitted, stored and transformed by aquatic systems before it makes its way to the ocean. As permafrost thaw, small ponds are formed and will last from days to millennia, depending on latitude, local geomorphology and ongoing erosion, precipitation regimes, and plant colonization. These ponds are generally large emitters of CH4 and CO2, with great variations in fluxes. For example, on Bylot Island (73°N), dissolved CH4 fluxes varied from 0.01 to 26 mmol m-2 d-1 (summers 2005-2011; N=160). Thaw ponds of the subarctic and arctic regions present very different limnological conditions in freeze-thaw and thermal regimes, light availability and microbial communities, which will largely influence direction and rate of emissions. With climate warming and changes in precipitation regimes, new ponds are forming while others are disappearing, but pond physicochemistry and microbial ecology is also quickly responding to climate, with potentially large consequences on GHG emissions. For example, warmer temperature and stronger stratification will promote methane production, and influence seasonal changes in emissions. On the other hand, primary production and methanotrophy may also increase, mitigating GHG emissions. The present study investigates the type of changes that are likely to occur in the near future and synthesizes our most recent findings on eastern Canadian subarctic and arctic thaw ponds.