VINCENT, W.F.; Universit� Laval, Qu�bec: Lake ecosystems at the northern limit of high Arctic Canada: extreme sensitivity to climate change
The northern coast of Ellesmere Island in the Canadian high Arctic (latitude 83N) is a region containing a variety of unique lake ecosystem types in which persistent ice plays a major role in their structure and dynamics. Five meromictic lakes occur in this area and are the result of isostatic uplift trapping basins of seawater that have been subsequently overlain by low conductivity melt water. The lakes are protected from wind-induced mixing by thick ice-cover through most or all of the year. As a result, they are highly stratified, with strong gradients in biological community structure and biogeochemical properties down their water columns that show some similarities with Antarctic lakes. Many of their features contrast substantially with Lake Romulus, a meromictic lake that lies in a warmer climate further to the south on Ellesmere Island. Thick perennial ice (greater than 3m) occurs on a freshwater lake on Ward Hunt Island, just off the coast of Ellesmere Island, and this waterbody is distinguished by a luxuriant benthic community of microbial mats dominated by cyanobacteria. A 400 km 2 expanse of ice occurs between the two islands (Ward Hunt Ice Shelf) and acts as a dam for inflowing meltwater in Disraeli Fjord of Ellesmere Island. The resultant ‘epishelf lake’ (freshwater overlying saltwater connected to the sea) contains a complex food web of microbial communities that support higher trophic levels. The ice shelf itself contains several dozen elongate (up to 30 km long) meltwater lakes which in turn are the habitat for unusual cryo-mat communities dominated by cyanobacteria, green algae and diatoms, but also containing viruses, bacteria, heterotrophic protists and microinvertebrates. This diversity of ecosystem types is vulnerable to relatively small changes in climate.
