Based on detailed analyses by the Intergovernmental Panel on Climate Change (IPCC), the Arctic is currently experiencing drastic changes including rapid rising temperatures and a severe decrease in sea ice cover. The warming of the northern coast of Ellesmere Island in the Canadian High Arctic is likely to be more rapid and of a greater amplitude than most other parts of the planet. Therefore, the focus of Dr Warwick Vincent research group (Université Laval) within Centre d?études nordiques is the great diversity of ecosystems found in that region. A particular interest is in aquatic ecosystems, specifically lakes and fjords. These are indicators of past and present environmental changes and will be subject to impacts caused by future climate change. The main objective of my doctoral thesis is to identify relevant aquatic indicators of environmental change for long term monitoring of Quttinirpaaq National Park in partnership with Parks Canada. The emphasis of this study is on the unique classes of epishelf and meromictic lake ecosystems. Epishelf lakes are ecosystems in which a layer of freshwater is in tidal contact with the sea in an ice-dammed fiord or embayment. Meromictic lakes are characterized through a permanent stratification of the water column due to a permanent ice cover. Both of these highly stratified ecosystems are physically fragile and depend on ice for their integrity. Vertical profiles including temperature and salinity are being analyzed each year to evaluate their susceptibility to environmental change. In situ microcosm experiments are also being performed to identify changes in phototrophic planktonic diversity due to variations in salinity that would be associated with mixing. As climate change alters the movement of contaminants in high latitudes, the burden of fluorinated contaminants such as PFOS and PFOA in aquatic food webs will be investigated in collaboration with Dr Derek Muir (Environment Canada). Finally, this approach based on multiple indicators will be applicable to the long term monitoring and management strategies of other protected areas in polar regions.