Evidence of Global Warming in North America's Northenmost Lake

The conclusion of a long-term study led by Université Laval scientists to determine the diversity and abundance of aquatic life-forms in Ward Hunt Lake -- a body of water located on a small island north of Ellesmere Island in the Canadian Arctic -- is that Ward Hunt Lake has undergone major transformations within the last two hundred years of its known 8,450 year history.

The researchers' conclusions are based on the final analysis of a lakebed sediment core extracted from the center of Ward Hunt Lake. This 18 centimeter long sediment core containing algae pigments and diatom remnants was used by the researchers as a biological archive in order to examine the history of aquatic life in Ward Hunt Lake.

The analyzes conducted by researchers from Université Laval's Center for Northern Studies reveal that Ward Hunt Lake, the North American continent's northernmost lake, is affected by climate change. The speed and range of aquatic transformations recorded in the sediment are unprecedented in the lake's 8,450 years. This suggests to the international team of researchers led by Warwick Vincent and Reinhard Pienitz that climate change related to human activity is at the source of this recent phenomenon.

Ward Hunt Lake is located on the 83rd parallel in the Quttinirpaaq National Park: quttinitpaaq means "top of the world" in Inuktitit. The Island of Ward Hunt, which houses Ward Hunt Lake, is completely surrounded by ice. The lake itself is permanently covered by a 4-meter layer of ice, except for a small peripheral zone, a zone around the edges, that thaws out during a few weeks of every summer.

"This is of course an extreme environment for living organisms, but our data indicate that current conditions make the lake a more favorable location for algae growth than it was in the past," points out lead author and Center for Northern Studies researcher Dermot Antoniades.

The deepest layers of the lake sediment, which correlate with the farthest reaches of the lake's history, contain only a small number of algae. There is also very little variation, or fluctuation, in the concentration of algae: a relatively stable algae community is evident in the deepest layers of sediment.

The top two layers--the top two centimeters of sediment--correspond to the last 200 years. These top layers show abrupt changes in the algae community in the lake. During the last 200 years, chlorophyll a--the green coloring matter in leaves and plants that is a carbohydrate produced by photosynthesis resulting from exposure to sunlight--which is a pigment found in every species in the lake, shows an increase by a factor of 500. The first appearance of a type of diatom--a unicelluar algae with silica in its cell wall--that is typical of very cold environments occurred during the most recent 200 years.

Antoniades said: "The absence of diatoms and the low pigment concentration below the top 2.5 centimeters of the core suggest that the lake was permanently frozen in the past." He further stated: "We cannot claim with certainty that these changes were brought on by human activity, but natural variations observed over the last millennia were never so abrupt and extensive."

This study was conducted as part of the ArcticNet program, which brings together scientists and managers in the natural, human health and social sciences with their partners in Inuit organizations, northern communities, federal and provincial agencies and the private sector to study the impacts of climate change in the coastal Canadian Arctic.

In addition to Antoniades, Vincent, and Pienitz, the article, which appears in the September 28 edition of Geophysical Research Letters, is co-authored by Catherine Crawley from the University of Toronto, Marianne Douglas from the University of Alberta, Dale Andersen from the Center for the Study of Life in the Universe (USA), Peter Doran at the University of Illinois in Chicago (USA), Ian Hawes from the National Institute of Water and Atmospheric Research (New Zealand), and Wayne Pollard from McGill University.

Jean-François Huppé, "North America's northernmost lake affected by global warming," Université Laval.