Imaging (and imagining) High Arctic Lakes

Guest post by Alexandre Normandeau

Maps of the lakes showing the detailed bottom bathymetry.  Blue and purple colours are the deepest areas.  

High Arctic Lakes are commonly used for environmental reconstructions because they are particularly sensitive to climate change. The Cape Bounty Arctic Watershed Observatory is probably one of the best examples of research sites that has shown the effect of climate change on landscape disturbances. The study of lake sediments can also provide information on natural hazards such as earthquakes and extreme flood events.  Ice cover is so pervasive on these lakes that it sometimes takes many years for conditions to occur that allow us to look into the lakes with modern research equipment.  After trying two previous years, in August 2015 we were finally able to finish surveying the lakes.

To analyze in great detail the history of natural hazards and climate change in the region, we brought very high-resolution echosounders in the High Arctic to map the bottom of the Cape Bounty’s lakes. These instruments emit soundwaves that travel to the bottom of the lake, and are reflected from the lakefloor before being recorded back by the echosounder. While commonly used echosounders are singlebeam (e.g., fishing echosounders), we use multibeam echosounders. This allows us to "see" on a 150° angle on each side of the boat, providing a complete image of the lake floor, similar to what Google Earth does for the land. These instruments are typically used on large research vessels and in accessible locations (near a road or human infrastructures). It was thus quite a challenge to bring our scientific equipment to such a remote location that is Cape Bounty. In collaboration with Université Laval, instead of using a large research vessel, we managed to fit our echosounder on a 7.5 m long zodiac. It is the first time that such an high-resolution mapping of lake floors is accomplished in the High Arctic.

Matt Gillman (M.Sc. student) on the Zodiac with the echosounders used in the High Arctic.

The data collected during the summer of 2015 was then corrected for vessel motion, lake-level fluctuations, sound refraction into the water, etc. The processed image of the lake-floor (Fig. 2) allowed us to understand sedimentary processes related to climate change (sea-level fluctuations, glaciations) and natural hazards (mass movements, floods).