Threat: Arctic permafrost melting emits harmful mercury in Alaska’s Yukon River

Considering the biggest carbon dioxide emissions, scientists have long focused on sequestering CO2 from the atmosphere. However, mercury emissions are of huge concern lately owing to the burning of coal mainly,  traceable to almost the entire energy industry value chain.

Recently, new research showed that the Arctic’s permafrost melts due to climate change because massive quantities of mercury trapped in frozen ground for thousands of years are now released into the Yukon River in Alaska.

The team of scientists from the University of Southern California (USC), in collaboration with Caltech, the Yukon River Inter-Tribal Watershed Council, MIT, and Delft University of Technology in the Netherlands, studied the impact of climate change on mercury release from permafrost in Alaska’s Yukon River Basin.

According to NASA, permafrost is any ground that remains completely frozen—32 degrees Fahrenheit (0 degrees Celsius) or colder—for at least two years straight.

As the permafrost thaws, this mercury has the potential to be released into the environment, posing significant ecological and health risks.

Frozen ice, a long-term threat to Earth

Past research has revealed that the Arctic permafrost likely contains about 1,656,000 metric tons of mercury, twice the amount in the rest of Earth’s soils, oceans, and atmosphere.

The sequestered mercury in ice could threaten the planet’s environment for a long time.

Mercury emitted into the Yukon River is likely to contaminate fish and wildlife, impacting the health of communities in the Arctic region and posing a threat to the livelihoods of living creatures.

The researchers also discovered that the river releases mercury from eroded permafrost and deposits some of it back onto riverbanks and sandbars.

The researchers said that over three million people live in areas where permafrost is projected to vanish entirely by 2050.

“There could be this giant mercury bomb in the Arctic waiting to explode,” expressed Josh West, co-author and professor of Earth sciences and environmental studies at the University of Southern California.

The co-author also stated that Earth’s natural atmospheric circulation tends to transfer pollutants to higher latitudes, resulting in mercury accumulation in the Arctic.

“Because of the way it behaves chemically, a lot of mercury pollution ends up in the Arctic. Permafrost has accumulated so much mercury that it could dwarf the amount in the oceans, soils, atmosphere, and biosphere combined,” West added.

Lives under threat in Alaska’s Yukon River region

The study was conducted near two northern villages in Alaska’s Yukon River Basin – Neaver and Huslia.

The team measured the total mercury (THg) concentrations in permafrost soils and floodplain sediments to evaluate the mercury concentration emitted into the Yukon River as permafrost thaws.

For better accuracy, the team tapped into the deeper soil layers and found that mercury levels were consistent with higher estimates from previous studies.

Isabel Smith, a doctoral candidate at USC Dornsife and the study’s corresponding author, says, “The river can quickly mobilize large amounts of sediment containing mercury.”

Estimations showed that the median total mercury (THg) levels in the sediment were 49 nanograms of THg per gram of sediment in Huslia and 39 nanograms per gram in Beaver.

Additionally, the ratio of mercury to organic carbon in these sediments was 5.4 gigagrams of THg per petagram of carbon in Huslia and 4.2 gigagrams per petagram in Beaver, with similar uncertainty ranges.

Satellite data also revealed the rapidly changing course of the Yukon River, affecting the mercury-laden sediments that are eroded from riverbanks and deposited along sandbars.

Curiously enough, scientists also found that finer grains contained more mercury than coarse grains, suggesting specific soil types that may pose greater risks.

“Considering all of these factors should give us a more accurate estimate of the total mercury that could be released as permafrost melts over the next few decades,” Smith says.

West explained the complexity of mercury sequestration in this case. He says the rivers are reburying a considerable amount of mercury. To really understand how much of a threat mercury poses, scientists have to understand both the erosion and reburial processes.

However, it could be devastating, especially for Arctic communities dependent on hunting and fishing.

“Decades of exposure, especially with increasing levels as more mercury is released, could take a huge toll on the environment and the health of those living in these areas,” added Smith.