Extreme Warming and Ecosystem Collapse in the Canadian High Arctic

Over the last ten years, several types of ice-dependent ecosystems in the High Arctic have experienced abrupt changes, including complete habitat loss at some locations. The latter includes the draining of a large epishelf lake as a result of partial break-up of the Ward Hunt Ice Shelf in 2002, and the loss of Ayles Ice Shelf and its associated microbial communities in 2005. In summer 2008, we recorded extreme warming at Ward Hunt Island and vicinity, at the northern limit of High Arctic Canada, with air temperatures up to 20.5C. This was accompanied by pronounced changes in microbial habitats: deepening of the permafrost active layer; loss of perennial lake ice and sea ice; loss of ice-dammed freshwater lakes; and 23% loss of total ice shelf area, including complete break-up and loss of the Markham Ice Shelf cryo-ecosystem. These observations underscore the vulnerability of Arctic microbial ecosystems to ongoing climate change, but also raise questions about when such events may have occurred in the past. There is anecdotal evidence that the 1930s was also a period of warm temperatures and ice shelf break-up in the High Arctic, and our modeling results for lake thermal regimes also imply a period of strong warming that time. To obtain a longer term perspective, we analysed coastal sediment cores taken behind the Ward Hunt Ice Shelf. The results indicate large variability in ice regimes throughout the Holocene, and imply that current ecosystem changes in the High Arctic are without precedent for 1600 years.