The ecosystems of the Canadian High Arctic, including freshwater systems, are recognized to be particularly vulnerable to the effects of global environmental change. Although freshwater systems of the High Arctic have undergone dramatic biotic shifts due to recent climatic change, very little information is available about the long-term responses of these systems to fluctuations in their environment. Paleolimnological records that use biological and geochemical indicators (including the diatoms and algal pigments) preserved in sedimentary profiles have the potential to provide detailed information on past climates and environments.
Epishelf lakes consist of a low density layer of freshwater that rests on a body of denser, colder salt water. They are typically formed when the fresh water from snowmelt and runoff from fiord catchments becomes confined behind ice sheets. Although this type of ecosystem is generally rare, and particularly in northern polar areas, some epishelf lakes have been identified in the northern part of Ellesmere Island.
Northern fiord systems can also become isolated from the sea following isostatic rebound. During this process, the epishelf systems often become meromictic lakes. These lakes, which are permanently density stratified because of the physical and chemical differences between surface and deep waters, often contain well-preserved fossil indicators in their sediments that allow high resolution reconstructions of environmental changes.
Our working hypothesis is that the epishelf lakes of northern Ellesmere Island record the historical changes in the external fresh water inputs, as well as the fluctuations in the glaciers that contain them. Since these variables are climatically controlled, the sediments of these epishelf lakes should contain records of long-term climatic change in the region. Moreover, our study of meromictic lakes should provide much additional information on the environmental history of this area of the High Arctic, including insights into the ontogeny of epishelf lake/meromictic systems, the chronology of the isostatic rebound, and high-resolution data on regional changes in high arctic climate.