Science The warming of the Arctic causes a sudden change in the ecosystem of North America’s deepest lake. Bella Brown October 24, 2023 Looking down from above, Great Slave Lake appears as a massive goose flying over Canada’s Northwest Territories. With a surface area equivalent to Belgium and maximum depths of 614 meters, it ranks as the 10th biggest freshwater lake globally and holds the title of North America’s deepest. The vast volume of frigid water has served as protection for Great Slave Lake against the effects of climate change that have disrupted the ecosystems of shallower lakes in northern latitudes. However, this is no longer the case, as stated in a recent research published in Proceedings of the Royal Society B. Due to the rapid warming of the Arctic, the microscopic algae, known as phytoplankton, at the base of Great Slave Lake’s food chain have undergone a major change in behavior since the start of the 21st century. These single-celled organisms, called diatoms, have shells made of silica that can be found in sediment records of the lake. Analysis of the sediment has revealed that the larger, chain-forming diatoms that were dominant in the lake have been replaced by smaller, flat-shaped counterparts. This shift in the primary source of energy could have an impact on the lake’s productivity and carbon levels, disrupt its food chain, and affect the availability of food and cultural resources for nearby First Nations and Métis communities. Profound Change, Cascading Consequences According to John Smol, a paleolimnologist from Queen’s University in Kingston, Ontario, Canada and a coauthor of the study, the recent changes in climate and decrease in ice cover have led to a significant shift. This change is expected to have far-reaching effects on the ecosystem, although the exact consequences are still unknown. In 2014, Smol and colleagues conducted a comparison of lake bottom cores with those taken in the mid-1990s. The two sets of cores provided sediment records dating back approximately 200 years, which were then analyzed for changes in diatom species abundance as an indicator of ecosystem transition. The sediments revealed that Aulacoseira islandica, a large and heavy diatom, dominated the lake’s ecosystem for most of the past century. However, in the mid-1990s, smaller and buoyant plankton, about one-tenth the size, began to take over. This transition increased significantly around 2000 and by the mid-2010s, the smaller plankton had completely taken control. This is a picture of Aulacoseira islandica, a type of diatom that was the most prevalent species in Great Slave Lake before 2000 (on the left). In the 21st century, the diatom population in Great Slave Lake has become more varied and now includes smaller organisms like Discotella (on the right). This photo was taken by K. Rühland from Queen’s University. The rapid and unprecedented shift in sediment records has surprised and worried lake researchers. While smaller and medium-sized northern lakes have been experiencing changes due to the warming climate since the mid-1900s, the discovery reveals that even large bodies of water like Great Slave Lake, which were once shielded by thick ice and thermal inertia, are now vulnerable to change. The impact and significance of these effects is surprising. Warwick Vincent, an ecologist at Laval University in Quebec, who specializes in Arctic lakes and was not part of the study, expressed surprise at the intensity and scale of the consequences. He had anticipated that North America’s deepest lake would have a significant ability to withstand the effects of global change, but it appears that this has been surpassed. Temperatures are increasing, ice cover is shrinking, and winds are decreasing. According to the lead author of the study, paleolimnologist Kathleen Rühland of Queen’s University, the sudden changes in Great Slave Lake are a direct result of the accelerating effects of climate change in the Arctic. The region is experiencing a much faster rate of warming compared to the global average, with a 1°C increase in average air temperatures since 2010. This has also led to a significant decrease in lake ice cover and a decrease in wind speeds in recent years. Rühland explains that these changes have made the lake calmer, which is problematic for large phytoplankton such as A. islandica, as they require turbulence to stay afloat and obtain light for photosynthesis. According to Rühland, they rapidly descend below the surface of the water. However, these circumstances are perfect for the smaller, flat diatoms that are more buoyant in nature. According to Rühland, the change in regime serves as an indication that significant changes are occurring. Further research and monitoring are necessary to determine the broader implications. A major question is how this shift will impact the production of algae, which is essential for the food system in this vast ecosystem. A study published in the journal Water using remote sensing found that between 2003 and 2018, primary production in Great Slave Lake increased by 27%. However, the smaller algae now fueling the food web may provide less nutrition for the organisms that consume them, ultimately affecting the food supply for fish and other aquatic life, as well as the communities that rely on them. Additionally, it is uncertain whether the new regime will sequester more or less carbon through primary production. The scientists are shifting their focus to the Great Bear Lake in the Northwest Territories, which is located even further north, experiences colder temperatures, and is even larger than the Great Slave Lake. Early findings on this lake, ranked as the eighth largest in the world, indicate that a similar disturbance is occurring there as well. According to Smol, the Arctic serves as a warning system for the planet, with its lakes acting as recorders. In these lakes, the algae can be seen as the “canaries.” “Cheryl Katz, a science writer, tweeted (@ckatz99)” Reference: Katz, C. (2023), The rapid warming of the Arctic causes a sudden change in the ecosystem of North America’s deepest lake, Eos, 104, https://doi.org/10.1029/2023EO230406. Published on October 24, 2023. The text is copyrighted in 2023 by the authors and is licensed under CC BY-NC-ND 3.0. Images are protected by copyright unless otherwise specified. It is prohibited to use them without the explicit consent of the copyright holder.