High above the Arctic Circle, far from the footprint of human civilization, a significant indication of human-induced climate change has manifested in Lake Hazen, the largest lake by volume north of the Arctic Circle. The lake and surrounding glacial environment are experiencing rapid change as the climate warms, ice cover declines, and glaciers retreat. A recent study in Nature Communications examines these physical drivers and their impacts on the lake’s ecological composition and the physiological condition of its only fish species, the Arctic Char. These changes, unprecedented in 300 years, have serious ramifications for local indigenous populations who rely on the lake’s ecosystem services.
In northern Ellesmere Island, the farthest north of the islands that compose the Canadian Arctic Archipelago, summer air temperatures increased by 1 degree Celsius during the 2001 to 2012 period in comparison to the period 1986 to 2000. Climate model simulations suggest temperatures are expected to increase 3.2 degrees Celsius by 2100. These changes have the potential to dramatically alter local ecosystems.
The study’s research team, which included experienced Arctic scientists from a diverse set of backgrounds, grew over time, according to Igor Lehnherr, who spoke with GlacierHub. From a scientific standpoint, the team knew that glacial masses were shrinking in other parts of the Arctic, along with summer lake ice cover. From this basis, according to Lehnherr, it was ”a matter of bringing everyone on board with all the different expertise required to quantify each of these various aspects.”
The study’s authors note that few previous studies have evaluated ecosystem-scale changes to climate change in inland watersheds. Lehnherr cited the need for a multidisciplinary team and baseline data to “quantify how much the system has changed and what drivers are responsible for ecological change” as challenges to study.
The researchers benefitted from over 50 years of scientific research on Lake Hazen, helping this recent study fill part of this knowledge gap by analyzing how the lake’s ecosystem has responded to climate change. The study does this through four distinct, yet interconnected focuses: watershed warming and declining lake ice cover, hydrological changes within the watershed, recent changes in the paleo-lake record, and ecological shifts in the lake itself.
Watershed Warming and Declining Lake Ice Cover
From 2000 to 2012, summer air temperatures in the Lake Hazen watershed rose by 2.6 degrees Celsius, with most of the rise occurring after 2007. These higher air temperatures, in turn, warmed the soil. Spring-time soil temperatures were 4 degrees Celsius higher from 2007 to 2012 than they were from 1994 to 2006. The lake warms particularly in late spring, when it is still covered by ice, and in early summer, when ice cover finally breaks up. Overall, the lake’s warming trend is causing ice to melt earlier in the summer and freeze later in the fall. This is in addition to an increase in ice-free area by 3 km2 per year since 2000, which was found to be related to August lake surface temperatures.
Hydrological Changes within the Watershed
Glaciers within the Lake Hazen watershed are the main hydrological driver. Because of warming temperatures, these glaciers are experiencing mass-balance losses. Positive feedback loops play a role in this loss, as high surface temperatures melt ice, subsequently decreasing reflectivity, which allows the surrounding surface to absorb more solar radiation, speeding up melting.
Mean rates of annual glacial runoff have increased significantly in recent years. This increase has raised water levels in Lake Hazen by almost a meter since 2007. Finally, the large increase in glacial runoff into Lake Hazen has lowered the time that water stays in the lake (before leaving by the lake’s one outflow stream) from a historical average of 89 years to 25 years today.
Recent Changes in the Paleo-Lake Record
The increase in glacial runoff entering Lake Hazen has driven sediment accumulation rates to levels eight times higher than a 1948 baseline period. Most runoff is deposited by glacier-fed rivers that empty into the lake, leading to the increased mixing and oxygenation of the lake’s once stable and anoxic bottom waters.
More sediment deposition has also given rise to increased levels of anthropogenic contaminants, such as mercury and pesticides, in lake sediments. In addition, organic carbon accumulation rates in the lake have increased by an astonishing 1000 percent, much higher than the 50 percent increase in most North American boreal lakes.
To assess the impact of the lake’s changes outlined above on its ecology, the authors used micro-fossil counts of algae. Before widespread warming (prior to 1890), when the lake was covered with ice almost year-round, algal fossils were rare. However, after warming (post 1890), when more areas of the lake became ice-free, nearshore algal species boomed.
After remaining relatively stable for much of the 20th century, the lake’s ecological composition changed in the late 1980s when planktonic species succeeded benthic species. This change was driven by a longer ice-free period where the deep waters of the lake were exposed to light for more months each year.
Lake Hazen’s one fish species, the Arctic Char, has also been negatively impacted by climate warming. Lehnherr notes that the team might have expected ice-free summers to increase the lake’s primary productivity, subsequently increasing biomass and leading to healthier and thriving Char populations. However, this has yet to occur; instead, amplified lake turbidity due to the raised levels of glacial river discharge has hindered the ability of the visually reliant Char to feed on midges and other Char, harming their physiological condition.
These changes have negative effects on the lake’s ecology and also on indigenous communities that inhabit the area. These communities rely on the lake as a source of food in an otherwise desolate region. While the future of High Arctic ecosystems is far from certain, Lehnherr points to the need for more multidisciplinary studies that encompass entire watersheds as a key to the better assessment of climate change impacts.